cryo systems review recommendation tracking report master · lcls-ii cd-1 director's review...

LCLS-II CD-1 Director's Review December 9-11, 2013

Review Recommendation Tracking Report

Recommendation No. 39 Status (Open, Closed, Ongoing): Closed

System Cryo

Owner Ross

Recommendation Study fall-back alternatives for cryogenic plants including their impact on cost and schedule. The first recommended alternative is to lower the operating temperature of the cavities to guarantee the Q0 value of 2.7x1010. The second recommended alternative is to increase the cooling capacity at 2 K to withstand lower Q0 values. These alternatives will demand to the team is charge to get expertise in 1.8 K refrigeration and/or in larger 4.5 K cryogenic plants. It will be an opportunity to improve the field of competences with an additional but limited risk with respect to the baseline scenario based on existing proven design.

Project Response Engineering Note LCLSII-4.5-EN-0185 provides an analysis of the interplay between cavity Q0 and gradient (dynamic heat load), and cryoplant capabilities, as a function of cavity operating temperature, with analysis of systems performance and trade-offs between cavity Q0 and cryoplant capabilities and costs. We conclude that, while the increase in Q0 at 1.8 K relative to 2.0 K may reduce overall cryogenic plant size by about 12%, cold compressor volumetric flow rate increases by about 50%, and one also needs an additional stage of cold compression. This complexity and cost increase over the nominally 2 K system outweigh the slight overall capacity advantage of the lower temperature operation. Thus, we have chosen 2.0 K as the operating temperature for the LCLS-II cryogenic system.


System Cryo

Owner Ross

Recommendation Create the SLAC Cryogenic operation team in advance, in order to prepare SLAC for operation of large cryogenic systems. This team will follow the installation of the cryogenic systems (FY18) and will participate to the commissioning (FY19). The corresponding personnel budget (15 to 20 FTEs) must be added.

Project Response The Project has made a permanent selection for the Cryogenics Systems group System Manager, and has completed the hire of two Cryogenics Systems engineers. The engineers will be initially stationed at Partner Labs to gain experience with their cryogenic systems. This group will be the nucleus of the SLAC Cryogenic operation team and will naturally lead the transition from installation to commissioning and operations. The group formed during the transition to operations near the end of the project will be supported by operations-personnel budget.

August 8, 2014


System Cryo

Owner Ross

Recommendation The cryomodule subcommittee recommends the following action prior to the call for tender for the cryoplant. The project should convene a technical review including international experts acting in an advisory role near the scheduled completion of the Qo R&D program.

• The project should charge the committee to assess the program status and advise on the choice of the cavity quality factor.

• The reviewers would, in addition, assess whether new techniques can be timely and effectively transferred to industry. • The committee would advise on detailed alternative plans that include a lower Qo and possible additional refrigeration capacity.

Project Response Project Management note LCLSII-2.6-PM-0052 documents the high-Q0 cavity R&D plan and milestones schedule including a final report that will be completed by end of November, 2014. This report will be internationally-reviewed. This will conclude after the completion of the procurement package and solicitation for the long-lead 4.5K coldbox. Alternative plans for increasing refrigeration capacity are discused in Engineering Note LCLSII-4.5-EN-0187. This has followed a more detailed assesment of cryogenic heatloads documented in Engineering Note LCLSII-4.5-EN-0179 and Functional Requirements Specification LCLSII-4.5-FR-0070, and is based on experience gained to date in the high-Q0 development program, other updated heat load assessments, uncertainty estimates based on data and analyses for all dynamic and static heat loads, and cryogenic plant overcapacity factor requirements.

3 recommendations

August 8, 2014

LCLS-II Conceptual Design Report Review January 14, 2014


Recommendation No. 1 Page 4 of CDR Review Report

Status: Closed Actual Date Closed: 6/20/14

System Cryo

Owner Ross

Recommendation Explore more alternative solutions related to linac cavities. Operation at lower Qload of 2.6x107 and bandwidth of 50 Hz with ca.7.6 kW per cavity, is an option that might be investigated. For the intrinsic quality factors there is an option of operation at 1.8K, which for nitrified cavities reduces dynamic heat load by 40%, and for two other treatments by 30%.

Project Response 11/11/14: Tests of a single cavity in a horizontal cryostat have demonstrated the instrumentation needed to study microphonics and cavity bandwidth issues. Further tests under increasingly realistic conditions for LCLS-II will be made as hardware becomes available. 6/20/14: 2.0 K remains the design baseline for the cryoplant design, and operating at lower Qload will be investigated during initial LCLS-II operation. 2/20/2014: We agree, that operating at lower Qext to increase bandwidth in order to mitigate microphonics is viable, and particularly so for the initial years of LCLS-II operation, when the average current is low. For the 240 kW beam power limit expected with the two initial undulator lines, we can halve Qload to 2x107, and with the nominal 6.3 kW power available per cavity, would still have enough RF power to double the detuning compensation to cover a 20 Hz bandwidth, with 15% RF power overhead. Operating the cryosystem at 1.8 K provides about 10% reduction in overall 4.5 K cryogenic plant size. At 1.8 K, however, the vapor density is about half that of 2.0 K vapor. After accounting for the improvement in Q0 one still has ~50% increase in volumetric flow through the cold compressor system. Thus, not only would another 1.8 K compression stage be required, but also larger cold compressors than the present state of the art, or parallel units in an untested configuration. Considering all these factors, we have selected 2.0 K as our baseline. We will continue to study temperature optimization as we gain more information about heat loads and cavity performance.

Recommendation No. 2 Page 4 of CDR Review Report


System Cryo

Owner Ross

Recommendation A low-loss cavity shape should be used for LCLS-II.

Project Response 11/11/14: The TESLA cavity remains the baseline choice for LCLS-II, with no shortcomings in performance or production being identified during the

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systems design evolution that warrant a change in cavity design. 2/20/2014: The choice of the TESLA accelerating cavity for LCLS-II is dictated by requirements to meet the project construction schedule and to maintain low technical risk in major systems. The TESLA cavity has demonstrated good electrodynamic performance and mechanical properties: low RF losses, high accelerating gradient, lack of multipacting (MP) in the operating gradient range, good damping of higher-order modes (HOMs), acceptable Lorentz force detuning (LFD), low sensitivity to He pressure fluctuations (df/dP), small response to vibrations, and good tuneability. The TESLA cavity has been thoroughly investigated by several groups worldwide; DESY, Fermilab and other Labs have extensive experience with this cavity over the past 20 years. TESLA cavity production, processing, preparation, handling and testing is well established. We recognize that the low-loss cavity provides modest (~15%) improvements in cryogenic losses. On the other hand, it is a relatively new cavity design and there is little experience with its performance, and thus it would require significant R&D in order to make it ready for adoption for the LCLS-II linac. Several issues would have to be addressed: (i) electromagnetic optimization, which is not limited by optimization of the operation mode, but includes MP investigations (numerical and experimental), HOM properties and damping of trapped modes, (ii) mechanical optimization (LFD, df/dP, tuneability, mechanical mode frequencies and transfer function), (iii) high–gradient tests for bare cavities, (iv) high–gradient tests of the dressed cavities, etc. Each of these explorations may result in additional cavity modifications and require repeating of the tests. This R&D process presents significant technical and schedule risk unacceptable to the project, as well as increased R&D cost.

Recommendation No. 3 of CDR Review Report


System Cryo

Owner Ross

Recommendation An investigation should be conducted to assess cryogenic plant liquid nitrogen (LN2) availability or operating the plant without LN2 assist.

Project Response 11/11/14: Further studies and a workshop on LCLS-II cryogenics systems support the choice of LN2 pre-cooling in the 4.5 K coldbox. A cryogenic workshop was held on Oct 28, 2014 and an engineering note is in the process of being written [ title ####, due date 12/1/14] to capture the conclusions and detailed response of the workshop and design features, including plant margin, operability and maintainability. Additionally, an Engineering Note titled Cryogenic Systems Process, LCLSII-4.1-EN-0327, has been written to detail the cryogenic systems operational configuaryions and flow diagrams. 2/20/2014: Bulk liquid nitrogen is available through a number of Bay Area based suppliers which include Airgas, Praxair, and Airco. Without LN2 assist, additional 4.5 K cold box turbo-expanders and warm helium compressors would be required, and civil infrastructure of electric utility, cooling water, and building space would have to be increased substantially, adding to the project cost. SLAC is currently procuring large amounts of LN2. At current available bulk LN2 pricing of about $.06/liter, and the current specified 4.5 K cold box LN2 usage rate of 560 L/hr, the LN2 cost based on

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8000 hours/yr is $269 k$/yr. For 4.5 K liquefaction without LN2, the warm helium compressor power increase would be approximately 607 kW or 291 k$/yr of electric utility cost (at an electric cost of $0.06/kW-hr). The cost of LN2 production is tied primarily to supplier production electric power costs which rise with the laboratory’s power costs. Although the present operational cost appears to “break even”, an estimated $3.5 M would have to added to the project capital equipment cost and installation for the required additional compressors, turbines, etc. if LN2 assist is not used. This does not include civil construction costs. This would also make the 4.5 K cold box a custom design leading to a longer lead time delivery, and this item is already on the project critical path. We believe LN2 assist presents the best technical choice based on capital expense, project schedule, and operating cost.

Recommendation No. 11 of CDR Review Report)


System Cryo

Owner Ross

Recommendation Technical risks associated with SC linac modifications needed to ensure CW operation should be more fleshed-out in the PDR, especially considering that no test facility is foreseen.

Project Response 11/11/14: A series of LCLS-II Engineering Notes has been written that address the major modifications needed for CW operation, and further studies have been made and were presented at the PDR. These details are captured in the FDR. 6/20/14: Technical notes addressing items 1-5 detailed below are drafted, and will be further discussed in the PDR. Pre-production cryomodules design and construction have begun and are schedule for testing Q1FY16. 2/20/2014: We agree, and plan to include in the PDR descriptions of the qualification and verification processes associated with each basic CM-design modification made for CW operation. The following modifications for CW operation are currently under consideration: 1) cavity high Q0 inert-gas surface-doping, 2) fundamental power coupler heat conduction improvement, 3) cryogenic two-phase line / helium vessel chimney diameter increase and CM two-phase line end cap modifications, 4) J/T expansion valve added to each cryomodule, 5) improved magnetic shielding and 6) possible microphonics reduction strategies. Each of these will be tested in either (or both) component test-stands (including cavity, fundamental power coupler, and magnetic shielding) or in a horizontal test cryostat (with two-phase line, J/T expansion valve, microphonics reduction) and some of these test results will be ready in time for inclusion in the PDR. In addition, the LCLS-II SC linac design is based on the European XFEL (XFEL) linac. For the basic technological aspects, not including CW operational considerations, we expect to be able to apply lessons learned during XFEL commissioning and cryomodule testing (first half of 2016) to our component assembly and testing plan. The first production LCLS-II cryomodules, after two pre-production units, will be completed around this time. Working with the DESY-based XFEL team, we will include more about general SC linac

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operation in the PDR.

Recommendation No. 14 Page 5 of CDR Review Report)


System Cryo

Owner Ross

Recommendation The mitigations needed to address the impact of variation in Q among the cavities should be considered.

Project Response 11/11/14: Cavities produced in the high-Q0 R&D program yield an average Q0 of 3.4x1010, indicating that the cryoplant capacity of 4 kW at 2 K is well within expected heat load including uncertainties. Mitigations for variation in cavity Q0 have been studied and documented in engineering note LCLSII-4.5-EN-0223. A single power amplifier per cavity configuration has been adopted,which simplifies optimized control and operation of cavities with different perfomance parameters. Work is proceeding in tests of nitrogen-doped high-Q0 cavities in horizontal test cryostats, to further understand variations in performance and to refine heat load expectations. Prototype LCLS-II cryomodule tests, scheduled to begin in 2016, will provide more definitive results. 6/20/14: Results of the High Q0 R&D effort will be presented and discussed in the PDR. Also an engineering note on simulations on production cavity performance has been drafted, and will also be discussed in the PDR. 2/20/2014: Characterization and quantification of the total linac heat-load is ultimately more important than cavity Q0 (taken individually) as this will determine the necessary cryoplant total heat-load removal capacity. Variations in Q0 (or heat load) are a second-order effect. These result from 1) differences in cavity manufacture, 2) differences in cavity surface processing, 3) field-emission or multipactor behavior, 4) differences in magnetic shielding or impact of spurious magnetic components, or 5) influence of spurious heating (for example in the end-groups) or poor cooling. The first three may be observed in the cavity qualification vertical test and the affected cavity may be returned to the production line for re-processing. The others may be observed in horizontal testing; which is foreseen for a fraction of the production cavities. Since the cryomodules are cooled in series, for the most part, as long as the variations are not so extreme that the cryomodule internal-cooling system is unable to provide adequate cooling, variations in cavity-to-cavity heat-load will be manageable as long as the average heat-load is maintained. Extreme cases should be detected in cryomodule test and may be mitigated through re-work. The PDR will include greater detail describing allowable heat-load variability limits. In terms of maximizing efficiency of the accelerating structures, adoption of a single-source single-cavity configuration throughout the linac will allow control of gradient in individual cavities, dependent on their Q0 and other operational characteristics.

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Status: Ongoing Planned Date Closed: 11/21/14

System Cryo

Owner Ross

Recommendation The capacity multiplier for the cryogenic system is marginal (29%). Typically, other projects assume at least 50%. This choice should be explained.

Project Response 11/11/14: A cryogenic workshop was held on Oct 28, 2014 and an engineering note is in the process of being written [ title ####, due date 12/1/14] to capture the conclusions and detailed response of the workshop and design features, including plant margin, operability and maintainability. The heat load estimated from baseline performance including average Q0 of 2.7x1010, is 3.54 kW @ 2 K including uncertainty factors of 30% for static and 10% for dynamic loads, as documented in LCLSII-4.5-EN-0179. The estimated dynamic load is 74% of the total 2 K heat load, and the Q0 of installed cavities dominates uncertainty in the total heat load. The target value of Q0 is ~35% higher than state-of-the-art in mass production, and ~35% lower than recent results for nitrogen-doped cavities. A 10% uncertainty in dynamic load reflects our confidence in achieveing the target Q0, based on results to-date. The cryoplant, based on the operational JLab 12 GeV systems, is designed for 4 KW capacity @ 2 K, allowing for an uncertainty of up to 27% in dynamic load. Cavities produced in the high-Q0 R&D program yield an average Q0 of 3.4x1010, indicating that the cryoplant capacity of 4 kW at 2 K is well within expected heat load including uncertainties. The high-Q R&D program will continue to refine our understanding of cavity performance and reproducibility, including horizontal tests of dressed cavities. The high Q0 surface process has been successfully transferred to two labs, with very good reproducibility, which gives us confidence that it can be transferred also to an experienced cavity vendor. Two prototype cryomodules, using 16 high Q0 cavites, will be built to confirm high Q0 cavity performance persists through cryomodule assembly. These prototype cryomodules allow first assessment of production cryomodule performance. If we miss the target Q0 by N%, then we need N% more refrigeration and no more cryomodules, or else ~2N% more cryomodules and no more refrigeration, or else some mix of these. Acquisition of a smaller-capacity plant for cooling a portion of the linac is another option that can support the Project schedule and offer other advantages, should experience with the prototype cryomodules demand.

Detailed documentation will be developed as experience with high-Q0 cavities progresses. 6/20/14: The cryoplant design is proceeding as planned, and will be reviewed after the results of the High Q0 R&D effort. Both will be discussed in the PDR. 2/20/2014: We believe a 29% overall plant capacity margin is reasonable based on recent successful designs such as the JLab 12 GeV 2 K upgrade which had a 19% margin and on which the LCLS-II refrigerator design is based. As the 2 K technology has evolved and demonstrated plant performance has been achieved the large margins of earlier cryoplant designs have been reduced. This, of course, did not apply to projects which have included near term future upgrades as part of the baseline project such as CEBAF from 4 to 6 GeV. Large sub-atmospheric plant capacity margins have presented operational

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problems at some plants, in terms of plant turn down and stability when the projected loads attained their planned values. An additional review of the overall cryogenic plant margin is planned prior to finalizing the plant specification. The decision process will be based on experience gained in our high-Q0 development program, other updated heat load assessments, uncertainty estimates based on data and analyses for all dynamic and static heat loads, and cryogenic plant overcapacity factor requirements.


Status: Open Proposed Date Closed: xxxxxxx 2015

System Cryo

Owner Ross

Recommendation It seems likely that 20-30% of cavities produced by industry will require a second chemical treatment to reach specification. The question needs to be answered how 20-30% of fully the dressed cavities can be re-nitrified.

Project Response 11/11/14: Cavities produced in the high-Q0 R&D program yield an average Q0 of 3.4x1010, indicating that the procedure is regularly produceing cavities exceeding Q0 performance. Work is proceeding in refining the nitrogen-doping procedure, and tests of nitrogen-doped high-Q0 cavities in horizontal test cryostats, to further understand variations in performance and to define the process for industrial production of cavities. This process will be documented in xxxxxxxx 2015. 6/20/14: The High Q0 R&D effort is on schedule, and will be presented in the PDR. 2/20/2014: Recent experience with major construction projects (CEBAF 12 GeV Upgrade, SNS, Eu-XFEL) and the intensive effort for ILC R&D has demonstrated that performance variability of SRF cavities given a consistent preparation protocol is associated with the presence of either structural fabrication flaws or extrinsic contamination. The former yields early quench; the latter yields either multipacting or field emission-induced electron loading, x-rays, dark current, and component activation. Use of qualified vendors using quality assurance processes remains the standard means of minimizing the occurrence of fabrication flaws. Similar enforcement of quality standards for final cleaning and assembly are required to avoid degradation by contamination. The intrinsic SRF properties of each cavity are determined by the content and structure of material to a depth of 100 nm from the surface. The great majority of cavities which have required a second cycle of “chemical treatment” have successfully met performance specification after a simple disassembly and recleaning with high-pressure ultra-pure water. This action is understood to only affect extrinsic surface contamination, leaving the cavity surface material unchanged. Within the set of 86 cavities prepared for the CEBAF 12 GeV upgrade, for example, only one failed to qualify after simple recleaning. That cavity, which had suffered accidental interior wall strikes with the high pressure rinse wand, was recovered to its required performance with a 5 micron electropolish, applied to the “fully dressed” cavity. The recently discovered nitrogen diffusion protocol is understood to yield

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beneficial performance by inhibiting the formation of lossy material within the RF penetration depth. The reduction of losses, observed as an increase in Q0, is due to population of defect sites in the niobium lattice by diffusion of nitrogen at high temperature (800°C). R&D is presently underway to define a robust diffusion protocol that is fully effective over a range of ~3-15 microns into the surface both to eliminate sensitivity to local variability of material removed, and also to provide the option for later “touch-up” electropolish if that should become necessary. No provision for repeated heat treatment and nitrogen diffusion at 800°C is believed to be needed. If significantly more chemistry removal were required for some reason, the helium vessel would have to be removed in any case to enable retuning of the cavity cells. Disassembly to such a state would also make vacuum rebaking and nitrogen diffusion possible, if needed.


Status: Open Planned Date Closed: April 2015

System Cryo

Owner Ross

Recommendation Overall availability of the cryogenic system as a whole needs to be assessed.

Project Response 11/11/14: A comprehensive and integrated Failure Mode and Effects Analysis (FMEA) and What-If Analysis will be developed for all three cryogenic sub-systems (cryomodules, cryogenic distribution system and cryoplant) prior to the last sub-system’s FDR. In addition, a Reliability, Availability, Maintainability and Inspectability (RAMI) analysis using the AvailSim code will be made to demonstrate that the system will meet the availability and reliability performance requirements for the LCLS-II facility, captured in LCLSII-1.1-PR-0163-R0. 6/20/14: Studies on linac availability will continue through the design phase of the system. 2/20/2014: Design for high availability of the full cryogenic system coupled with operational, maintenance, and failure mode analysis are part of the CD-2 work plan. Demonstrated whole system engineered availabilities of existing cryomodule/distribution system/cryogenic plant availability have met 99%+, as demonstrated by JLab CEBAF and SNS 2K system. This level of availability is the goal for the full LCLS-II cryogenic system during the project engineering and design phase.


Status: Ongoing Actual Date Closed: March 2016

System Cryo

Owner Ross

August 8, 2014

Recommendation A long term test of nitrified cavities seems to be necessary to determine how

stable the Q0 enhancement by that procedure is.

Project Response 11/11/14: Work is proceeding in tests of nitrogen-doped high-Q0 cavities in horizontal test cryostats, to further understand variations in performance and to refine heat load expectations. Prototype LCLS-II cryomodule tests, scheduled to begin in 2016, will provide more definitive results. 6/20/14: Extensive testing on both cryomodule pre-production units will be performed at both partner laboratories in FY16. 2/20/2014: It is well recognized that many factors contribute to the Q0 of SRF cavities realized in operation. Realizing the low-loss character needed for LCLS-II will require controlling all of them. It is helpful to distinguish intrinsic and extrinsic sources of effective RF losses. The application of deliberate diffusion of nitrogen into the RF surface at high temperature (800°C) to a depth of approximately 10 microns is understood to have beneficial effect by inhibiting the formation of lossy material that otherwise forms quite naturally, thereby nearly eliminating one intrinsic source of losses, the one responsible for “mid-field Q drop”. The nitrogen atoms preferentially occupy defect sites in the niobium lattice. It is precisely because these atoms settle into such low energy states at 800°C that one expects them to remain locked in place indefinitely at room temperature and cryogenic temperatures. On this basis one expects the concomitant reduction of RF losses, and increase in Q0, to be quite robust and durable. Tests of a N-doped cavity over a 6-month period, the longest duration achieved to date, show negligible change in measured Q0 as a function of gradient. The durability should be comparable to the benefit observed by 120°C post-chemistry bake applied to electropolished niobium cavities to eliminate the “high-field Q slope”, in that it durably changes material structure within the surface. One must recognize, however, that this treatment effects the elimination of but one source of RF losses. The more familiar magnetic field induced residual losses and losses due to extrinsic surface contamination remain to be controlled by preparation and environmental cleanliness and local magnetic material management. Control requirements on those factors become more stringent for LCLS-II in order to fully glean the benefits from lowering intrinsic losses via the surface nitrogen diffusion. The project recognizes this and will solidify and implement the corresponding quality assurance measures. We will continue to measure N-doped cavities to build experience with their performance over time.

9 recommendations

August 8, 2014

LCLS-II CD-1 Technical, Cost, Schedule and Management Review February 4-6, 2014



System Tech Sys 2.5 - Cryo System

Owner M. Ross

Recommendation Re-evaluate the margin for the plant capacity to support the procurement.

Project Response We believe a 29% overall plant capacity margin is reasonable based on recent successful designs such as the JLab 12 GeV 2 K upgrade which had a 19% margin and on which the LCLS-II refrigerator design is based. As the 2 K technology has evolved and demonstrated plant performance has been achieved the large margins of earlier cryoplant designs have been reduced. Engineering Note LCLSII-4.5-EN-0187 includes review of the overall cryogenic plant margin. This has followed a more detailed assesment of cryogenic heatloads documented in Engineering Note LCLSII-4.5-EN-0179 and Functional Requirements Specification LCLSII-4.5-FR-0070, and is based on experience gained in our high-Q0 development program, other updated heat load assessments, uncertainty estimates based on data and analyses for all dynamic and static heat loads, and cryogenic plant overcapacity factor requirements.



Owner M. Ross

Recommendation Re-evaluate the cryogenic distribution system segmentation to optimize phased installation, commissioning, operation availability, maintainability and future upgrades (due by CD2).

Project Response We have re-evaluated cryogenic distribution system segmentation and optimization, and documented results in an LCLS-II Engineering Note LCLSII-4.5-EN-0187.



Owner M. Ross

Recommendation Address previous review committee recommendations (due by CD-2).

Project Response The project has responded to all previous review recommendations and we have documented these in a series of Engineering Notes.

August 8, 2014


System Tech Sys 2.6 – Cryomodules

Owner M. Ross

Recommendation Use a risk-based methodology to optimize the cryomodule design. The optimization should support long term-facility reliability and maintenance goals by August 2014.

Project Response The LCLS-II cryomodule design methodology has been documented in an Englneering Note LCLSII-4.5-EN-0186, and features are captured in the Functional Requirements Specification LCLSII-2.5-FR-0053-R0.


System Tech Sys 2.6 - Cryomodules

Owner M. Ross

Recommendation Establish clear milestones/steps and decision criteria for selecting the final Q0 by August 2014.

Project Response A plan and milestones schedule has been produced that includes 36 single-cell process optimization tests, and 19 nine-cell treatment and vertical-test cycles completed by October 6, 2014, and 6 fully-dressed cavity horizontal-tests completed by October 31, 2014. The goal of the tests is to: 1) show the effective high- Q0 cavity performance of an industrial-quality process, 2) show that the technology can be transferred from one institution to another, and 3) show that high-Q0 cavity performance can be transferred from a vertical-test dewar to the cryomodule-like horizontal-test cryostat. These tests are to be carried out at the three LCLS-II partner labs, Fermilab, Jefferson Lab and Cornell University and each will prepare a final report that will be submitted on or before November 17, 2014. The plan is documented in Project Management note LCLSII-2.6-PM-0052.

5 recommendations

August 8, 2014

LCLS-II Facility Advisory Committee Review July 1-2, 2014


Recommendation No. 19 Status: Closed Planned Date Closed: 09/12/14

System Cryogenic Systems – High-Q Superconducting RF Cavity R&D

Owner Ross

Responder Ginsburg

Recommendation We recommend a follow up with similar R&D for 3.9 GHz cavities.

Project Response The project plans to fund a limited high-Q0 optimization program for 3.9 GHz cavities. A proposal similar to that formulated for 1.3 GHz is in progress. Elements of the proposal include development of a nitrogen doping process and studies of the impact of cool down scheme on magnetic flux trapping. The work for 3.9 GHz cavities can be significantly streamlined because of the understanding achieved from the 1.3 GHz development.


System Cryogenic Systems - Cryoplant Specifications

Owner Ross

Responder Pischalnikov

Recommendation Experience at DESY shows that piezo elements used in a feedback loop can generate heat, which would add to the heat load at 2 K. The committee recommends to study piezo behavior, measure generated heat and account for it in the total dynamic heat load.

Project Response The tuner design and microphonics control team is aware of heat generation from piezo operations. The LCLS-II piezo tuner design uses a piezo-stack at relatively low voltage compared with the XFEL tuner, and the heat load on the piezo scales as the voltage squared. Based on the DESY study and estimations for the LCLS-II design, the heat generated by the LCLS-II piezo will be approximatley 1–2 W. The piezo generated heat will be thermally intercepted at the 5 K level, or perhaps even at 40 K.

The team at FNAL has built a specialized test stand to study lifetime of piezo under cold/insulated vacuum environment. They are conducting a piezo-tuner longevity program, which will include study of heat generation from piezo operation. One concern is that warming of the piezo can lead to decreased longevity of the piezo tuner. DESY/XFEL experts have expressed interest in this program and would like to be involved.

August 8, 2014



Owner Ross

Responder Corlett

Recommendation The committee recommends evaluating benefits of adding additional access port for tuners vs. additional cryomodule design complication, cost, and reliability (possible vacuum leaks, etc.). Present this at the next review.

Project Response Tuner access ports are desirable in facilitating inspection and maintenance of cavity tuner components, and the tuner is designed to allow accesss to the motors, drive mechanism, and piezo stacks, through ports in the cryomodule vacuum enclosure. Accommodating the fundamental power coupler on the aisle side of the cryomodule requires the tuner ports to be on the opposite side or "back" of the cryomodule, toward the wall when installed in the SLAC linac tunnel. Tuner ports will be included in the prototype cryomodules, and will be readily accessible during initial tests in the cryomodule test stands. Accessibility in the SLAC tunnel is more challenging. Design features to allow access when installed in LCLS-II are being studied, and will be reviewed as part of the final cryomodule design development process.



Owner Ross

Responder Corlett

Recommendation Develop an approach for rapid cool down through transition of the entire linac as well as individual cryomodules, and present at the next review.

Project Response An initial study has been performed, that suggests that the required rapid cooldown rate is feasible for a single or few cryomodules using the current cryoplant and cryo-distribution designs, and with the addition of a valve and some piping of the 2 K LHe distribution within each cryomodule. The concept has been discussed within the Cryo Systems team, and will be further developed and documented, and incorporated in the final design.



Owner Ross

Responder Adolphsen

Recommendation Develop an approach for field emission mitigation and show how the approach taken for LCLS-II meets specifications.

Project Response Field emission, in particular the resulting ionizing radiation, will first be

August 8, 2014

measured in the cavity vertical tests. Cavities exhibiting field emission at low gradient (< 13 MV/m) will likely be reprocessed (high pressure rinse) to remove the high field emission sources - this has generally been shown to work at JLAB and DESY. Field emission will also be measured (as both ionizing radiation and captured current) cavity by cavity in the cryomodule Test Stands. Also all cavities will be operated at 16 MV/m to evaluate the net cryomodule 2K heat load. If it is determined that one or move of the cavities are having a significant impact on the 2K heat load, or they are producing excessive radiation, they will be processed with He gas (i.e. run rf with the cavities filled with low pressure He) - in this process the He ions created from the field emission electrons bombard the cavity surface, reducing the emission current (likely from smoothing the surface). JLAB has show that this process increases the field emission gradient threshold by typically 5 MV/m. Finally, the cavities can be run at higher gradients burn off the emission - this may require exciting other same-band monopole modes (e.g. 8π/9) to prevent quenching in other parts of the cavity that are not field emission limited. Cornell has had some success with this approach. When the cryomodules are operating in the tunnel, we will also measure radiation levels to look for "hot" (field emitting) cavities if the overall cryoload is near the plant limit. Perhaps He processing could be used in this case, but would require a major interruption of operation.



Owner Ross

Responder Peterson

Recommendation Simulate mechanical modes of oscillation for the whole cryomodule in order to compare with results from prototype cryomodule tests.

Project Response Fermilab is presently performing Finite Element Analyses of the LCLS-II cryomodule structure so as to understand natural mechanical oscillation frequencies, acceleration limits imposed by support structure stress limits, and to verify compliance with California and SLAC seismic regulations. Simulation results for natural frequencies will be compared with measurements of the prototype cryomodules to help verify the model and verify our understanding of the structural limits and behavior. This analysis will be complete in advance of the prototype cryomodule FDR in January, 2015



Owner Ross

Responder Corlett

August 8, 2014

Recommendation Develop a cryogenic system upgrade plan for the case where additional

capacity would be required after the facility is in operations. Make sure that the cryo system design accommodates future expansion with minimal modification of the installed hardware.

Project Response The estimated heat load is 3.54 kW @ 2 K including uncertainty factors of 30% for static and 10% for dynamic loads, as documented in LCLSII-4.5-EN-0179. The estimated dynamic load is 74% of the total 2 K heat load, and the Q0 of installed cavities dominates uncertainty in the total heat load. The target value of Q0 is ~35% higher than state-of-the-art in mass production, and ~35% lower than recent results for nitrogen-doped cavities. A 10% uncertainty in dynamic load reflects our confidence in achieveing the target Q0, based on results to-date. The cryoplant, based on the operational JLab 12 GeV systems, is designed for 4 KW capacity @ 2 K, allowing for an uncertainty of up to 27% in dynamic load. The high-Q R&D program will continue to refine our understanding of cavity performance and reproducibility, including horizontal tests of dressed cavities. The high Q0 surface process has been successfully transferred to two labs, with very good reproducibility, which gives us confidence that it can be transferred also to an experienced cavity vendor. Two prototype cryomodules, using 16 high Q0 cavites, will be built to confirm high Q0 cavity performance persists through cryomodule assembly. These prototype cryomodules allow first assessment of production cryomodule performance. If we miss the target Q0 by N%, then we need N% more refrigeration and no more cryomodules, or else ~2N% more cryomodules and no more refrigeration, or else some mix of these. Possible improvements in cooling capacity beyond that achieved by the existing JLab plant are under consideration and, if feasible, will be pursued before procurement of critical components. Acquisition of a smaller-capacity plant for cooling a portion of the linac is another option that can support the Project schedule and offer other advantages, should experience with the prototype cryomodules demand. Detailed documentation will be developed as experience with high-Q0 cavities progresses.

7 recommendations

August 8, 2014

Cryo Systems Preliminary Design Review and Integrated Safety Review August 13-15, 2014


Recommendation No. 1 Status: Closed Planned Completion Date or Date Closed: 09/03/14

System SC-3: Cryogenics

Responder Corlett

Recommendation Consider the addition of a smaller cryogenic plant (approximately 1 kW) to serve the L0 and L1 segments of the linac. This would increase the cryogenic plant margin in the L2 and L3 segments and would allow for phased commissioning of the linac.

Project Response The option to add a smaller cryoplant to cool the upstream SRF components has been documented in LCLSII-4.5-EN-0187 "Cryogenic Plant Design, Segmentation and Upgrade Options". A separate 500–1,000 W at 2.0 K cryogenic plant allows further segmenting the cryo distribution such that the four linac sections (L0–L3) are each independently cooled strings of cryomodules. The supplemental plant would cool strings L0 and L1, the main plant would cool L2 and L3. This configuration allows increased cryogenic heatload margin as well as greater flexibility including phased commissioning of the strings, and keeping the Linac cold at 4.5 K by using the small plant, etc.



Responder Corlett

Recommendation Review the uncertainty factor for dynamic loads or study and document the risks and mitigation actions in case of significant degradation of nitrogen doped cavities with time and/or the reduced performance/reproducibility after industrialization.

Project Response Update 11/11/14

A cryogenic workshop was held on Oct 28, 2014 and an engineering note is in the process of being written to capture the conclusions and detailed response of the workshop and design features, including plant margin, operability and maintainability. The estimated heat load is 3.54 kW @ 2 K including uncertainty factors of 30% for static and 10% for dynamic loads, as documented in LCLSII-4.5-EN-0179. The estimated dynamic load is 74% of the total 2 K heat load, and the Q0 of installed cavities dominates uncertainty in the total heat load. The target value of Q0 is ~35% higher than state-of-the-art in mass production, and ~35% lower than recent results for nitrogen-doped cavities. A 10% uncertainty in dynamic load reflects our confidence in achieveing the target Q0, based on results to-date. The cryoplant, based on the operational JLab 12 GeV systems, is designed for 4 KW capacity @ 2 K, allowing for an uncertainty of up to 27% in dynamic load. Cavities produced in the high-Q0

August 8, 2014

R&D program yield an average Q0 of 3.4x1010, indicating that the cryoplant capacity of 4 kW at 2 K is well within expected heat load including uncertainties. The high-Q R&D program will continue to refine our understanding of cavity performance and reproducibility, including horizontal tests of dressed cavities. The high Q0 surface process has been successfully transferred to two labs, with very good reproducibility, which gives us confidence that it can be transferred also to an experienced cavity vendor. Two prototype cryomodules, using 16 high Q0 cavites, will be built to confirm high Q0 cavity performance persists through cryomodule assembly. These prototype cryomodules allow first assessment of production cryomodule performance. If we miss the target Q0 by N%, then we need N% more refrigeration and no more cryomodules, or else ~2N% more cryomodules and no more refrigeration, or else some mix of these. Acquisition of a smaller-capacity plant for cooling a portion of the linac is another option that can support the Project schedule and offer other advantages, should experience with the prototype cryomodules demand. Work is proceeding in tests of nitrogen-doped high-Q0 cavities in horizontal test cryostats, to further understand variations in performance and to refine heat load expectations. Prototype LCLS-II cryomodule tests, scheduled to begin in 2016, will provide more definitive results. Detailed documentation will be developed as experience with high-Q0 cavities progresses.



Responder Klebaner

Recommendation Evaluate the potential cost reduction of combining the upstream and downstream distribution boxes into a single distribution box; further, consider combining the distribution boxes and the interface box.

Project Response Updated 09/19/14

Utilizing two independent distribution boxes for the connection between the cryoplant and the linac cryomodule strings provides for both the primary function of supporting the various operating modes, and also for positive isolation of the two distribution lines for initial installation and any subsequent maintenance/repair activities. By combining the 2 K cold box, interface box and distribution boxes into a common unit, the need for the interface box will be eliminated. Responses to a Request for Information, seeking a cost effective technical approach to combining the 2 K cold box and the distribution box, have been received from industrial vendors. A workshop involving cryoplant and cryo distribution teams will be held in October 2014 to determine the best approach.



Responder Theilacker, Colocho

August 8, 2014

Recommendation Conduct a comprehensive and integrated Failure Mode and Effects Analysis

(FMEA) and what if analysis of the entire cryogenic systems scope.

Project Response Updated 09/19/14

A comprehensive and integrated FMEA and What-If Analysis will be developed for all three cryogenic sub-systems (cryomodules, cryogenic distribution system and cryoplant) prior to the last sub-system’s FDR. In addition, a Reliability, Availability, Maintainability and Inspectability (RAMI) analysis using the AvailSim code will be made to demonstrate that the system will meet the availability and reliability performance requirements for the LCLS-II facility, captured in LCLSII-1.1-PR-0163-R0.



Responder Corlett

Recommendation Seek a cost strategy that will allow for a change to the one amplifier per RF cavity topology throughout the linac. The flexibility offered by this topology change will be invaluable during commissioning and operations.

Project Response A proposal for single source single cavity RF power configuration has been developed and presented to the LCLS-II Project Management team, including cost estimate. The team is currently considering this as potential scope change.



Responder Corlett

Recommendation Develop contingency plans in case the prototype cryomodules are not suitable for installation in the linac.

Project Response The niobium procurement includes options for sufficient raw material to build an additional 16 cavities, or two cryomodules worth. A decision on exercising this option and planning for build-out of additional cryomodules will be made based on experience gained in operation of the prototype cryomodules



Responder Miller

Recommendation Consider using cost incentives or alternative strategies to achieve early delivery of the cryogenic plant.

Project Response LCLS II will consider using the most effective alternatives to obtain the

August 8, 2014

earliest possible delivery of the cryogenic plant to include cost incentives or liquidated damages (LDs) if determined appropriate on a case by case basis. LDs are viewed collectively by the LCLS II Procurement team as an ineffective means to motivate early performance while cost incentives, if meaningful and appropriate are effective tools. On a case by case basis, these tools will be considered for use in motivating contractors towards early completion along with any other feasible alternative strategies. Frequent and on-going communications with vendors are considered critical aspects of the contract administration phase of the work. JLAB intends to have frequent dialogue with vendors to solve issues at the earliest opportunity to preclude schedule delays.



Responder Miller

Recommendation Assess and consider mitigation actions such as penalties and/or incentives in case of underperformance or delays of subsystems impacting interfaces or the overall project.

Project Response Response to recommendation 7 above addresses also these issues. In addition, rarely, if ever, would we use monetary incentives to motivate a contractor performing poorly. Liquidated damages/penalties are not considered effective strategies and would most likely increase pricing proposals to LCLS II. Best value source selection techniques are tools the significantly reduce the risk of selecting poor vendors and are used on virtually all major procurements on the LCLS II project.



Responder Neil

Recommendation Reassess Jefferson Lab infrastructure plans and processes in view of systematic Qo degradation from vertical test to cryomodule performance for the 12 GeV upgrade cavities.

Project Response Jefferson Lab has commissioned new chemistry, cleanroom, assembly and associated facilities after the 12 GeV upgrade cryomodule production run. Critical utilities, water, have been upgraded as well. There are significant technical improvements in all cases. Process development (travelers, procedures) specifically for the LCLS II cryomodule production run will be developed by a team at Jeffeson Lab. This team will include scientific, engineering, and production staff participation to ensure the best possible performance for LCLS II cryomodules.

August 8, 2014



Responder Cutino

Recommendation Develop a schedule and priority for the completion of the ODH analyses that takes into consideration the procurements and project needs. This schedule should be incorporated into the project master schedule to assure the timely completion of needed calculations.

Project Response The ODH analyses are dependent upon finalized failure mode and effects analyses of cryomodules, cryogenic distribution systems and cryoplant, which is dependent upon complete design for each item as well as the integrated cryosystem. A preliminary classification of the ODH hazard for the tunnel, klystron gallery, and cryoplant will be completed by 9/16/14. An ODH System FRS will be complete by August 2015, approximately the same time as the Cryo System FDR. The initial version may need to be updated as 3.9 GHz CM design will not be finalized until 2016.

Recommendation No. 11 Status: Ongoing Planned Completion Date or Date Closed: 11/21/14


Responder Arenius, Ravindranath

Recommendation Document the process simulations of the existing 12GeV plant for the maximum, nominal, and minimum LCLS-II load requirements in an official engineering note.

Project Response Updated 09/19/14 Update 11/11/14

A cryogenic workshop was held on Oct 28, 2014 and an engineering note is in the process of being written to capture the conclusions and detailed response of the workshop and design features of the cryoplant. An engineering note documenting the cryoplant design is now being written, and will be competed in advance of beginning formal procurement activities. This note will document the cryogenic heatloads and the capability of the 2 K plant to adapt to the sizable load variations. Process calculations and flow diagrams for all operating modes will be documented, including cooldown, stabilized intermediate temperatures, fast cooldown, 4.5 K and 2 K nominal operation, and independent control of temperatures for various linac sections.



Responder Peterson

Recommendation Develop an engineering note for the heat load/relief sizing requirement for the insulating vacuum vessel relief devices (lift plates) and for the beamline vacuum relief burst disk(s).

August 8, 2014

Project Response We will write an engineering note for the relief sizing requirements for the

vacuum spaces. For the insulating vacuum system, analyses are in progress regarding flow rates for worst-case scenarios. There will be one large insulating vacuum relief on each cryomodule. A tuner access port on each cryomodule may serve double-duty as the location of the large insulating vacuum relief. For the beam vacuum, venting flow rates are much lower and can be accommodated by rupture disks outside of the cryomodule string on the beam pipe at or near each of the cryogenic end boxes. These considerations, analyses, and design results will be documented in our engineering note.

Recommendation No. 13 Status: Ongoing Planned Completion Date or Date Closed: November 2014


Responder Peterson

Recommendation Perform a study to demonstrate that the cryoplant and distribution system can achieve fast cooldown and high gradient rates as required to obtain the high Q0 performances before the procurement specification of the 4.5K coldbox is finalized.


An initial study has been performed, that suggests that the required rapid cooldown rate is feasible using the current cryoplant and cryo-distribution designs, and with the addition of a valve and some piping of the 2 K LHe distribution within each cryomodule. The concept has been discussed within the Cryo Systems team, and will be further developed and documented, and incorporated in the final design. An initial analytical study has been performed that suggests that a rapid cooldown rate, if required, is feasible using the current cryoplant and cryo-distribution designs. Cool-down of individual cryomodules for better control of cavity cool-down conditions, so as to maximize temperature gradient for sweeping out magnetic flux, will be achieved via isolation of the warm-up/cool-down manifold (Line H) within each cryomodule from the next, the addition of a J-T valve within each cryomodule to supply that cool-down manifold individually for each cryomodule, and some additional piping of the 2 K LHe distribution within each cryomodule. Requirements for cryomodule cryogenics circuits under conditions of fast cooldown from 40K are documented in LCLSII-4.5-EN-0179-R1. Experimental studies are under way in horizontal and vertical cavity tests as well as more detailed analyses of cavity cool-down. Testing of entire strings of cavities will not be done until tests of the prototype cryomodules in 2016, but horizontal cryostat tests will provide essential verification of analyses which can be extended to full cryomodules.



Responder Hays

August 8, 2014

Recommendation Review or implement a comprehensive global integrated schedule with key

project interlink between subsystems.

Project Response Cryo Systems activities will be included in the LCLS-II Project logically-linked and milestone-driven project schedule, which will be baselined 09/30/2014.



Responder Corlett

Recommendation Make a comprehensive review of all existing requirements and their implementation in the subsystem requirements documents with appropriate review and release.


The LCLS-II Project manages requirements in a flowdown of information through Technical Requirements Documents in the form of GRD, PRDs, FRS's, ICD's, RDS's, and ESD's. Each document is posted for review by impacted engineers, systems managers, and physicists, with signature approval obtained from the appropriate design authorities as determined by the LCLS-II Quality Assurance Manager. The process is defined in the Systems Engineering Management Plan (LCLSII-1.1-PM-0043). Additionally, Cryo Systems has hired a system integration engineer, with responsibilities including tracking and verification of the implementation of system physics requirements, engineering specifications, and interfaces. We have developed a spreadsheet for comprehensive tracking of requirements and specifications, with links to appropriate documentation. This spreadsheet is being used by systems physicists, CAMs, and design engineers to ensure complete and accurate documentation.



Responder Hays

Recommendation Implement a more rigorous and effective approach to the verification and implementation of flown-down requirements and interface requirements coherency and completeness.

Project Response Cryogenic Systems has hired a system integration engineer, with responsibilities including tracking and verification of the implementation of system physics requirements, engineering specifications, and interfaces.



Responder Healy

August 8, 2014

Recommendation Review the seismic requirements specifications to implement, where

required by the integrated safety analysis, not only the structural requirements but also the maintaining of the functionalities during a seismic event for safety equipment.

Project Response The Project will perform the SLAC required integrated safety analysis/analyses and identify any components or systems that are to be considered as safety systems. The seismic design criteria for those systems will be updated accordingly to meet code requirements for safety systems.



Responder Cutino

Recommendation Review the risks for the LN2 ODH outside the building according to the proposed layout and potential presence of low accumulation points, galleries or trenches, or simply due to an accidental release during a cryogen transfer.

Project Response The risks for LN2 will be addressed as part of the overall integrated ODH analysis. A preliminary classification of the ODH hazard including outdoor areas will be completed by 9/16/14.



Responder De Barger

Recommendation Establish a process to manage exceptions that may arise between the partner labs on the pressure vessel safety program.

Project Response The LCLS II QA Program process for managing issues of nonconformance provides for the proper notification of the concern, the selection of responsible individuals to disposition the nonconformance, and the appropriate documentation to record the event and establish corrective action. Formal procedures are established to afford consistent implementation throughout the Project, and all partners in the LCLS II collaboration will adhere to this this process by either adopting the Project Office Nonconformance process, or applying their own similar methods and documentation previously approved by the LCLS II QA Manager. Approval from the appropriate authority or authorities at each affected institution will be obtained at the time a procurement is prepared for placement. In the specific case of pressure systems (both ASME and non-ASME), consistent with the process contained in the ASME BPVC, any nonconformance will be documented in a nonconformance report which shall be reviewed by the Quality Control Manager at the facility performing the work and the proposed disposition shall be approved by the Authorized Inspector at the facility performing the work. Conflicts or disagreements will be referred to the LCLS-II Quality Assurance Manager for resolution.

August 8, 2014



Responder Skonicki

Recommendation Develop a process akin to the approach taken with pressure vessel safety to manage quality system deviations or non-conformances as they arise.

Project Response The LCLS II QA Program has developed a process for managing issues of nonconformance. The process provides for the proper notification of the concern, the selection of responsible individuals to disposition the nonconformance, and the appropriate documentation to record the event and establish corrective action. All LCLS II sites, including the Partner Labs, will apply this process by either adopting the Project Office Nonconformance process, or applying their own similar methods and documentation previously approve by the LCLS II Manager. Formal procedures were established to afford consistent implementation throughout the Project.

20 recommendations

August 8, 2014

LCLS-II Director’s Status Review August 19-21, 2014




Owner Ross

Recommendation Define the sample size for the Qo validation program which shows that the Qo will be adequately preserved in the final linac, prior to the next DOE review.

Project Response The high-Q R&D project documented in LCLSII-PM-8.2-0052 "High Q0 R& D Plan" is aimed at developing confidence in processes which will lead to industrial production of cavities averaging ≤10 W/cavity heat load at 16 MV/m when installed in cryomodules. Acceptance test criteria for cavities delivered by vendors are to be established, and will follow the XFEL example of demonstrated successful fabrication following procedures and specifications provided by the Project. The LCLS-II Project bears responsibility for cavity performance. Currently there are six tests planned of dressed cavities in horizontal test stands: three on the HTS at FNAL, and three in the HTC at Cornell. These tests address, among other topics, the environmental conditions needed to preserve high-Q0 performance in the more complicated test conditions than single-isolated-cavity vertical test. Success in these tests when outfitted with the full complement of ancillary hardware, will constitute a proof-of-principle that high-Q0 performance can be adequately preserved in the final linac. Significant additional challenges to Q-preservation will occur in the string assembly, beamline assembly, “magnetic hygiene” of the cryomodule design and construction, and the cooldown thermal profile controls provided by the cryomodule design and engineered cooldown process. This hardware and process engineering design is in progress. Success at demonstrating Q-preservation in the initial testing of the two prototype cryomodules will be a major part of our Q0 validation program. This would validate the clean assembly processes at the two collaborating Labs. Since material sources and design changes will occur between the prototype cryomodules and the production cryomodules, some uncertainty will yet exist until the first pair of cryomodules from each of the two production lines are successfully tested.



Owner Ross

Recommendation Document, prior to the next DOE Review, a plan to address the impact of underperforming Qo in the completed linac.

Project Response The estimated heat load is 3.54 kW @ 2 K including uncertainty factors of 30% for static and 10% for dynamic loads, as documented in LCLSII-4.5-EN-

August 8, 2014

0179. The estimated dynamic load is 74% of the total 2 K heat load, and the Q0 of installed cavities dominates uncertainty in the total heat load. The target value of Q0 is ~35% higher than state-of-the-art in mass production, and ~35% lower than recent results for nitrogen-doped cavities. A 10% uncertainty in dynamic load reflects our confidence in achieveing the target Q0, based on results to-date. The cryoplant, based on the operational JLab 12 GeV systems, is designed for 4 KW capacity @ 2 K, allowing for an uncertainty of up to 27% in dynamic load. The high-Q R&D program will continue to refine our understanding of cavity performance and reproducibility, including horizontal tests of dressed cavities. The high Q0 surface process has been successfully transferred to two labs, with very good reproducibility, which gives us confidence that it can be transferred also to an experienced cavity vendor. Two prototype cryomodules, using 16 high Q0 cavites, will be built to confirm high Q0 cavity performance persists through cryomodule assembly. These prototype cryomodules allow first assessment of production cryomodule performance. If we miss the target Q0 by N%, then we need N% more refrigeration and no more cryomodules, or else ~2N% more cryomodules and no more refrigeration, or else some mix of these. Possible improvements in cooling capacity beyond that achieved by the existing JLab plant are under consideration and, if feasible, will be pursued before procurement of critical components. Acquisition of a smaller-capacity plant for cooling a portion of the linac is another option that can support the Project schedule and offer other advantages, should experience with the prototype cryomodules demand. Detailed documentation will be developed as experience with high-Q0 cavities progresses.



Owner Ross

Recommendation Provide for individual rapid cool down of cryomodules by final design.

Project Response An initial study has been performed, that suggests that the required rapid cooldown rate is feasible using the current cryoplant and cryo-distribution designs, and with the addition of a valve and some piping of the 2 K LHe distribution within each cryomodule. The concept has been discussed within the Cryo Systems team, and will be further developed and documented, and incorporated in the final design.



Owner Ross

Recommendation Retain the tuner access ports in the final cryomodule design

Project Response Tuner access ports are desirable in facilitating inspection and maintenance of cavity tuner components, and the tuner is designed to allow accesss to

August 8, 2014

the motors, drive mechanism, and piezo stacks, through ports in the cryomodule vacuum enclosure. Accommodating the fundamental power coupler on the aisle side of the cryomodule requires the tuner ports to be on the opposite side or "back" of the cryomodule, toward the wall when installed in the SLAC linac tunnel. Tuner ports will be included in the prototype cryomodules, and will be readily accessible during initial tests in the cryomodule test stands. Accessibility in the SLAC tunnel is more challenging. Design features to allow access when installed in LCLS-II are being studied, and will be reviewed as part of the final cryomodule design development process.



Owner Ross

Recommendation Combine the 2 K cold box, interface box and distribution boxes into a common unit without compromising the ability to independently thermal cycle either cryomodule string

Project Response We are in process to issue a request for information to industry seeking a cost effective technical approach to combining the 2 K cold box and the distribution box. By combining these two boxes, the need for the interface box will be eliminated.

5 recommendations

August 8, 2014

LCLS-II DOE Status Review September 30 – October 2, 2014


Recommendation No. 11 Status: Ongoing Planned Date Closed: March 2016

System SC5 – Cryo System

Responder Peterson

Recommendation Launch immediately a full scale LCLSII cavities string cool down rate and scheme validation test to assess the technical risks and perform a study to demonstrate that the cool-down rate requirements can be achieved by the cryogenic plant and distribution system. Due by Jan 2015 (Prototype 1.3GHz Cryomodule FDR)

Project Response An initial analytical study has been performed that suggests that a rapid cooldown rate, if required, is feasible using the current cryoplant and cryo-distribution designs. Cool-down of individual cryomodules for better control of cavity cool-down conditions, so as to maximize temperature gradient for sweeping out magnetic flux, will be achieved via isolation of the warm-up/cool-down manifold (Line H) within each cryomodule from the next, the addition of a J-T valve within each cryomodule to supply that cool-down manifold individually for each cryomodule, and some additional piping of the 2 K LHe distribution within each cryomodule. Requirements for cryomodule cryogenics circuits under conditions of fast cooldown from 40K are documented in LCLSII-4.5-EN-0179-R1. Experimental studies are under way in horizontal and vertical cavity tests as well as more detailed analyses of cavity cool-down. Testing of entire strings of cavities will not be done until tests of the prototype cryomodules, but horizontal cryostat tests will provide essential verification of analyses which can be extended to full cryomodules.

Recommendation No. 12 Status: Ongoing Planned Date Closed: June 2015


Responder Hays

Recommendation Provide a risk mitigation plan integrated in the current project schedule to document all the options investigated in term of costs, benefits, impact, technical difficulties or as part of an upgrade path. (Due by June 2015 CDS FDR)

Project Response A risk is carried in the project risk registry that considers cryomodule Q0 degradation or failure to achieve an average Q0 of 2.7x1010 as specified by the system physics requirements. The result of realizing the risk would be to exercise one or multiple upgrade options for cryogenic systems that include additional refrigeration capacity and/or the addition of cyromodules to the linac. Triggers for the risk, which are from milestones in the project schedule, are: 1) Completion of the High Q0 R&D program, 2) Q0 defined for Production cavities, 3) Prototype Cryomodule testing complete. For additional refrigeration capacity, we have planned a series of cryoplant

August 8, 2014

technical meetings, which review the current capabilities for the baseline plant and establish upgrade paths for additional cryogenic capacity. The first was held at JLAB on 28 October 2014, and the second is scheduled for December 18, 2014 at FNAL. For additional cryomodules, we have/will included options in the procurements for additional long-lead components such as Nb material for cavities. Exercise-by dates for these options have or will be included in the project schedule.

Recommendation No. 13 Status: Ongoing Planned Date Closed: November 21, 2014


Responder Arenius

Recommendation Revisit CD-1 recommendations. Perform a comprehensive review regarding plant margin, operability and maintainability. Due by March 2015.

Project Response A cryogenic workshop was held on Oct 28, 2014 and an engineering note is in the process of being written [ title ####, due date 12/1/14] to capture the conclusions and detailed response of the workshop and design features, including plant margin, operability and maintainability. Additionally, an Engineering Note titled Cryogenic Systems Process, LCLSII-4.1-EN-0327, has been written to detail the cryogenic systems operational configurations and flow diagrams.

Recommendation No. 14 Status: Ongoing Planned Date Closed: April 2015

System SC6 - Cryomodules

Responder Corlett

Recommendation Fully complete the CD-1 Recommendation regarding long-term operability before the cryomodule final design review. (April 2015)

Project Response A comprehensive and integrated Failure Mode and Effects Analysis (FMEA) and What-If Analysis will be developed for all three cryogenic sub-systems (cryomodules, cryogenic distribution system and cryoplant) prior to the last sub-system’s FDR. In addition, a Reliability, Availability, Maintainability and Inspectability (RAMI) analysis using the AvailSim code will be made to demonstrate that the system will meet the availability and reliability performance requirements for the LCLS-II facility, captured in LCLSII-1.1-PR-0163-R0.

Recommendation No. 15 Status: Ongoing Planned Date Closed: January 2015


Responder Romanenko

August 8, 2014

Recommendation Perform a detailed magnetic shielding analysis before prototype cryomodule

final design review. (January 2015)

Project Response Studies of residual magnetic field and shielding requirements are documented in LCLSII-4.5-EN-0222 "Magnetic Shielding: Requirements and Possible Solutions", and LCLSII-4.5-EN-0310-R0 "A Study of Magnetic Shielding Performance of a Fermilab International Linear Collider Superconducting RF Cavity Cryomodule". These support the conclusion that it is feasible to achieve magnetic field values at the level of 5 milliGauss for a cryomodule in a realistic and representative ambient magnetic field environment. Additional studies and experiments are currently being conducted and will be documented in engineering notes.

Recommendation No. 16 Status: Closed Planned Date Closed: October 2014


Responder Thielaker

Recommendation Perform alignment verification during prototype cryomodule testing. Incorporate into the design by the prototype final design review. (January 2015)

Project Response The prototype cryomodule design does not include features necessary to perform alignment verification, and it is not intended to add such features. We believe the LCLS-II cryomodules alignment will behave essentially the same as the cryomodules already tested at DESY, and will be within the required tolerances for cavity, BPM, and magnet positions and angles. The cavity alignment following cool down has been analytically analyzed by DESY as well as Fermilab. The Fermilab analysis is documented in a Fermilab engineering document ED0001152 (in the FNAL Teamcenter database). The best method for verifying the thermal contraction model is by passing an electron beam through the cryomodule. This has been done with the same type of cryomodule at the DESY FLASH free electron laser facility which has been operational for over a decade. With the number of cryomodules used in FLASH, the project feels confident in the predictability and repeatability of the active component alignments in the LCLS-II cryomodule. The first two type III cryomodules produced at Fermilab for the ILC collaboration incorporated wire position monitors (WPM). The purpose of the WPM was to monitor bowing of the 300 mm gas return pipe during cool down. Bowing of the pipe places cool down constraints on the cryomodule; both differential temperature and cool down rate. Although the WPM was incorporated in these initial cryomodules to only monitor the gas return pipe, results can be used to verify part of the thermal contraction model. Results of WPM data during cool down have been documented in presentations: Type 2 Cryomodule

“On Line Monitoring of the TTF Cryostats Cold Mass with Wire Position Monitors”, A. Bosotti, C. Pagani and G. Varisco, INFN/TC-00/02, March 17, 2000.

Type 3+ cryomodule Module #6 Test in CMTB, A. Bosotti, March 20, 2007.

August 8, 2014

“A Wire Position Monitor System for the 1.3 GHz Tesla-Style Cryomodule at the Fermilab New-Muon-Lab Accelerator”, N. Eddy, et. al., 15th International Conference on RF Superconductivity, July, 2011.

6 recommendations: 1 closed, 5 ongoing (1 will not be closed by due date)

August 8, 2014