november 6, 2007-beijing (zisman) global design effort 1 perspective on lbnl-ihep damping ring edr...
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November 6, 2007-Beijing (Zisman) Global Design Effort 1
Perspective on LBNL-IHEP Damping Ring EDR Activities
Michael S. ZismanCenter for Beam Physics
Accelerator & Fusion Research DivisionLawrence Berkeley National Laboratory
November 6, 2007-Beijing (Zisman) Global Design Effort 2
Introduction (1)• LBNL has a long history of participating in
storage ring designs for HEP– PEP, PEP-II, NLC-DR, ILC-DR
• Main LBNL activity in ILC is DR work– this is where we wish to focus
• LBNL participated in global DR planning effort via S3 task force– M. Zisman A. Jackson– M. Venturini
• LBNL is providing DR leadership for ART also– M. Zisman A. Jackson; also M. Palmer (Cornell)
November 6, 2007-Beijing (Zisman) Global Design Effort 3
Introduction (2)• Tasks of interest for DR EDR effort
– magnet design, vacuum system design, feedback system design, diagnostics design, mechanical integration, kicker design, injection/extraction, RF cavity design
• Also interested in beam dynamics R&D efforts– e.g., e-cloud, fast ions, impedance-related issues
• Some non-DR ILC tasks also of interest– overall timing/synchronization system
• of relevance to linac
– general magnet and vacuum system design• of relevance to RTLs and BDS
November 6, 2007-Beijing (Zisman) Global Design Effort 4
Introduction (3)• We have a history of successful
collaboration with IHEP– PEP-II quadrupoles fabricated and measured
here– PEP-II dipole fabrication supervised by IHEP
• and these magnets also measured here
• We have an MOU with IHEP in place to facilitate collaborative activities
• And...we like Chinese food!
November 6, 2007-Beijing (Zisman) Global Design Effort 5
People & Resources• ILC-ART resources
– $795k in FY07 • 2.2 scientist FTEs• 0.4 engineer FTEs
– $1751k in FY08• 2 scientist FTEs• 1 engineer FTE
• Additional manpower support from “core” program
• People contributing:– J. Byrd, D. Bates, C. Celata, S. DeSantis, M. Furman, A.
Jackson (program leader), S. Marks, D. Plate, G. Penn, I. Reichel, R. Schlueter, M. Venturini, J-L Vay, M. Zisman
• FY09 support will likely increase if overall ILC R&D budget does
– unfortunately, this is not a given
November 6, 2007-Beijing (Zisman) Global Design Effort 6
Responding to R&D Priorities• We continue to contribute to critical areas of DR EDR
needs by developing new capabilities and leveraging existing LBNL expertise and resources
• Already engaged in, or plan to start, activities in the following very high-priority R&D areas:– Electron cloud (ongoing)– Fast ion instability (measurements at ALS planned later this year)– Single-bunch instabilities (ongoing)– Low-emittance tuning – 650 MHz cavity design
• Additional activities include– Lattice optimization, single particle dynamics, wiggler modeling
(ongoing) – Characterization of space-charge effects (mostly completed)– Design of prototype kicker meeting DR specification (to be tested at
ATF/KEK); characterization of CSR at ATF/KEK (ongoing)– Multi-bunch instability, feedback systems, transients
• Vacuum design and mechanical integration (RDR EDR)
November 6, 2007-Beijing (Zisman) Global Design Effort 7
Suppression of e-cloud• Change of baseline has elevated rank of e-cloud R&D
– must demonstrate that e-cloud build-up can be suppressed to the level where it is harmless
• Suppression techniques being investigated include grooved chambers and clearing electrodes (+ more “conventional” surface coatings) – measurements conducted at PEP-II will test both proposed remedies.
Design of chamber w/ CE for experiment at PEP-II by D. Plate, LBNL
Proposed design of grooved chamber for PEP-II
experiment
Electrode, Copper 0.04” x 1.0” x 50.0”(49.606” between feedthrough centers)
Electrode, Copper 0.04” x 1.0” x 50.0”(49.606” between feedthrough centers)
November 6, 2007-Beijing (Zisman) Global Design Effort 8
e-cloud in Grooved Chambers • Simulations show that triangular groove geometry with a
sufficiently steep angle can suppress e-cloud effectively
To mitigate impedance, rounding the tips would be desirable …
… but it spoils the effectiveness of grooves
Max. longitudinal density of e– accumulated through a 111 e+ bunch train in DR dipoles drops by 100 for =75o
Simulations done w/ augmented version of POSINST (Venturini, Furman) max=1.75
November 6, 2007-Beijing (Zisman) Global Design Effort 9
Wiggler Modeling and Simulations
• Progress in e-cloud experiments/measurements and simulations must go hand in hand
• Making a substantial investment in characterizing e-cloud in wigglers, a significant issue for DRs – use/expand integrated code suite WARP/POSINST (already
successfully tested for HCX heavy ion experiment here at LBNL)
– study both e-cloud build-up and e-cloud induced instabilities
– ultimate-goal, a fully self-consistent simulation, very challenging but within reach
• LBNL to – model e-cloud measurements in
wigglers– design wiggler vacuum chamber
with clearing electrodes
Wigglers installed at CESR-c have inspired the technology choice for
current DR baseline
Proposed e-cloud experiment at CesrTA
November 6, 2007-Beijing (Zisman) Global Design Effort 10
3D e-Cloud Code Development
• Using WARP-POSINST code– beam and cloud evolve self-consistently (PIC)– refined mesh gives efficient calc. of beam
evolution– calculates in moving frame (~ 1000x speedup)
proton bunch radius vs. z
CPU time:• lab frame: >2 weeks• frame with 2=512: <30 min
CPU time:• lab frame: >2 weeks• frame with 2=512: <30 min
J.-L. Vay, PRL 98, 130405 (2007)
2D benchmark shows excellent agreement
November 6, 2007-Beijing (Zisman) Global Design Effort 11
Wiggler Vacuum Chamber Concept
• Wiggler vacuum chamber is a warm-bore insert – not integral to cryostat
• Design assumptions:– machined, welded aluminum
with antechamber– photon power absorbed within
chambers by copper absorber– pumping: NEG wafers mounted
on heater for regeneration– integral cooling to minimize
thermal load during regeneration
– NEG coating for reduction of secondary electrons
• LBNL provided mechanical integration for the DRsS. Marks, D. Plate, R. Schlueter
Tubular Heater Water Cooled
Absorber
NEG Coating
NEG
NEGNEG
NEG
10
120
60
R23
Cooling for NEG Activation
Vacuum chamber for quadsin wiggler section
Wiggler vacuum chamber
November 6, 2007-Beijing (Zisman) Global Design Effort 12
Fast Ion Instability
• Experimental validation of present fast ion instability models essential for DRs but largely unaccomplished
• New set of measurements planned for ALS promises to provide the required validation (Byrd, Steier)
• Use grow/damp techniques to measure growth rate under varying machine conditions and bunch train structure.
• First experimental evidence of Fast Ion Instability produced at ALS (ca. 1996, J. Byrd et al.)
100
80
60
40
Vert
ical
RM
S s
ize (
µm
)
403020100
Number bunches
He added nominal pressure
No. of bunches in bunch trainy-
rms
size
m
with He
nominal pressure
November 6, 2007-Beijing (Zisman) Global Design Effort 13
Single-bunch Longitudinal Instabilities • To avoid unacceptable emittance degradation down the
linac, collective instabilities can’t be tolerated– otherwise, DRs can be “source of all evil” (Anonymous from SLAC)
• Collaboration w/SLAC for characterization of single-bunch dynamics based on detailed modeling of impedance sources– goal: benchmark available tools and methods
Mode analysis of linearized Vlasov Eq. for longitudinal Motion may fail to give accurate Characterization of instability Venturini, ILC-DR06 Workshop
Mode analysis of linearized Vlasov Eq. for longitudinal motion may fail to give accurate characterization of instability Venturini, ILC-DR06 Workshop
Mode analysisMode analysis
Vlasov Eq. solutionin time domain
Vlasov Eq. solutionin time domain
Good agreement
No agreement
Mode analysis
November 6, 2007-Beijing (Zisman) Global Design Effort 14
Influence of Space-Charge• Equilibrium emittance in a non-ideal lattice
modified by space charge – radiation envelope formalism extended to account for
effective modification of linear lattice due to space charge (Venturini et al.)
• Formalism being extended to include IBS
Equilibrium vertical emittance for 200random realizations of sext. displacementw/o space charge …
Equilibrium vertical emittance for 200random realizations of sext. displacementw/o space charge …
… with space charge. Effect is small (current lattice)
… with space charge. Effect is small (current lattice)
November 6, 2007-Beijing (Zisman) Global Design Effort 15
Dynamic Aperture Studies
• Frequency maps indicate presence of harmful resonances and suggest ways for lattice optimization
• OCS6 lattice suffers from reduced degree of symmetry – different working point and harmonic sextupoles improve dynamic
aperture
Nominal DR lattice Improved lattice
regularmotion
chaoticmotion
x=52.40y=49.31
x=52.30y=49.275
I. Reichel, LBNLx (mm)
y (m
m)
y (m
m)
e+ at injectionx (mm)
November 6, 2007-Beijing (Zisman) Global Design Effort 16
Kicker Technology• ATF/KEK is test bench for DR kicker technologies (pulsers, striplines,
loads, feedthroughs,…) with specification close to or exceeding DR requirements
• Contributing to design of ATF striplines kicker structures:– demonstrate 5 mrad deflection, 2.8/5.6 ns bunch separation; stringent
requirements on field decay time (DR specs: 3.1/6.2 ns; 0.6 mrad)– transform voltage pulse into a deflecting field efficiently w/o introducing
undesired beam impedance– produced a kicker design; estimated impedance; transients analyzed
trailing bunch enters module
Time transient analysis
z (m)
Snapshot of field when trailing bunch Is in the middle
0.7% fluct..
S. De Santis
Energy stored vs. time
9 ns
Detail of the mesh (with coax for modeling bench measurement of impedance
November 6, 2007-Beijing (Zisman) Global Design Effort 17
Meeting Kicker Specifications
variation < 1% over 5 mm
250
200
150
100
50
0
70006000500040003000200010000
Frequency (MHz)
Longitudinal impedance (loss factor ~ 0.1 V/pc)
Analysis of deflecting field uniformity
Bunch at kicker’s
mid-length
Bunch at kicker’s
mid-length
x (mm)
• Specifications likely to be met for 5.6 ns– no pulser currently available with required
rise/fall time characteristics at 2.8 ns
• Residual uncertainty mainly connected with the development of high-voltage, high-repetition rate feedthroughs
Minimizing impedance and high-order modes
Minimizing impedance and high-order modes
Z (
)
High Order Modelocalized by the feedthrough
November 6, 2007-Beijing (Zisman) Global Design Effort 18
Universal Accelerator Parser:Undoing the Tower of Babel
• Different accelerator analysis programs use different input formats to describe a lattice
• The UAP library will provide a way to translate input files between various accelerator codes
Fred designs a complicated beamline using MADFormat: SIF
Eric wants to simulate this using PLACETFormat: SIF doesn’t workNeed to translate deck to PLACET’s native dialect!
Brian wants cross-check the result using ELEGANT
Algernon wants to do some BDSIM work
A Tower of Babel:
D. Bates in collaborationwith D. Sagan, A. Wolski
• Ease the way of using multiple platforms to study a complex accelerator system
November 6, 2007-Beijing (Zisman) Global Design Effort 19
Instrumentation and Feedback
• Transverse feedback [Barry, Byrd]– develop model to assess noise, gain, phase
margins– design prototype low-noise receiver
• Injection noise [Byrd, Penn]– characterize sources of jitter and develop tools
for transient analysis– assess implications for feedback system design
November 6, 2007-Beijing (Zisman) Global Design Effort 20
LLRF Activities (1)• Continued work on LLRF design for HINS
– suitable for ILC also
• Objectives– determine stability with multiple loads (HINS)– characterize state-of-the-art components
(HINS)– examine scalability + high-volume production
capability•In collaboration with SNS
•4 14-bit 80 MS/s digitizers
•2 14-bit DACs
•Xilinx Spartan-3 FPGA
•USB interface
•Bench tested and working
November 6, 2007-Beijing (Zisman) Global Design Effort 21
LLRF Activities (2)• Initial test results
– 2.5 bits rms wideband noise– clock jitter < 0.5 ps rms
• Modeling– goal: to improve understanding of single
klystron with multiple cavities• study microphonics noise at klystron and cavity• understand feedback configuration and system
stability
November 6, 2007-Beijing (Zisman) Global Design Effort 22
Areas of Mutual Interest• Recent completion of BEPC-II has greatly
enhanced IHEP’s technical strengths
• Areas where collaboration seems natural include– hardware
• vacuum, magnets, power supplies, feedback, diagnostics, LLRF
– simulations• lattice design, dynamic aperture, low-emittance tuning• instabilities
– impedance-driven, e-cloud, fast-ion
• Both areas could include a joint experimental program at BEPC-II and ALS
November 6, 2007-Beijing (Zisman) Global Design Effort 23
How To Work Together• Assign contact persons from each institution
– suggest Jie Gao (IHEP); Alan Jackson (LBNL)
• Next, we should together select a few key areas and technical problems on which to collaborate– e.g., vacuum, lattice/dynamic aperture, feedback
• choose topics already funded either by ART or core program
• Selected collaborators should meet initially in person– followed by phone conferences to continue the
technical interactions• propose overall deliverables
– define milestones and dates
November 6, 2007-Beijing (Zisman) Global Design Effort 24
Summary• LBNL has made significant contributions to the DR
design found in Baseline Configuration Document and RDR
• We wish to continue a strong role in ILC-DR design and focus on critical R&D areas needed to complete the EDR: – Beam dynamics
• Electron cloud (characterization of e-cloud in wigglers; assistance with design of experiments and data analysis)
• Fast Ions (measurements and validation of theory)• Collective effects (space-charge effects for RTML lines; estimate of
single-bunch threshold instabilities based on numerical impedance modeling)
• Low-emittance tuning • Study of transients at injection/extraction
– Engineering, design of technical systems• Kickers, feedback, LLRF, vacuum, mechanical integration
• An LBNL-IHEP collaboration will increase technical strength of DR EDR effort– and enhance contributions of both institutions