the control system for the cryogenics in the lhc tunnel icec 22 - 45... · 2015. 3. 17. ·...

The control system for the cryogenics in the LHC tunnel Gomes P1, Anastasopoulos K2, Antoniotti F1, Avramidou R2, Balle Ch1, Blanco E1*, Carminati Ch1, Casas J1, Ciechanowski M3, Dragoneas A2, Dubert P3, Fampris X2, Fluder Cz3, Fortescue E1, Gaj W3,Gousiou E2, Jeanmonod N1, Jodłowski P3, Karagiannis F2, Klisch M3, Lopez A1, Macuda P3, Malinowski P3, Molina E4, Paiva S1, Patsouli A2, Penacoba G1, Sosin M3, Soubiran M1, Suraci A1, Tovar A1, Vauthier N1, Wolak T3, Zwalinski Ł3 1 CERN Accelerator Technology Department, Geneva, Switzerland (*Accelerators & Beams Department) 2 National Technical University, Athens, Greece 3 AGH University of Science and Technology, Kraków, Poland 4 CIEMAT, Madrid,Spain

The Large Hadron Collider makes extensive use of superconductors, in magnets for bending and focusing the particles, and in RF cavities for accelerating them, which are operated at 1.9 K and 4.5 K. The process automation for the cryogenic distribution around the accelerator circumference is based on 16 Programmable Logic Controllers, each running 250 control loops, 500 alarms and interlocks, and a phase sequencer. Spread along 27 km and under ionizing radiation, 15 000 cryogenic sensors and actuators are accessed through industrial field networks. We describe the main hardware and software components of the control system, their deployment and commissioning, together with the project organization, challenges faced, and solutions found.

INTRODUCTION

The Large Hadron Collider (LHC) at CERN is a 27 km proton-proton accelerator-collider, lying some 100 m underground; it will soon be operational and will eventually reach the unprecedented energy of 7 TeV per beam and luminosity of 1034 cm-2s-1 [1].

The LHC (Fig. 1) has eight Insertion Points (IPs), separated by sectors of about 3.3 km each. Four of these points are dedicated to the main experiments (P1-ATLAS, P2-ALICE, P5-CMS, P8-LHCb), while two others are used for beam cleaning (P3, P7), one for the beam dump (P6), and another for the RF accelerating system (P4).

Each sector comprises: a curved section of 2 460 m (called ARC), with 23 regular cells of 107 m in a continuous cryostat; a dispersion suppressor (DS, 170 m) at each extremity of the ARC, and a long straight section (LSS, 270 m) near each IP.

In the ARC, every cell contains two sets of 3 steering dipoles and 1 focusing - defocusing quadrupole; all the ARCs and DS together comprise 1 232 main dipoles and 392 main quadrupoles. Both of these types of superconducting magnets operate in superfluid helium at 1.9 K, in order to reach respectively a field of 8.3 T, and a field gradient of 223 T/m, when powered to 11.8 kA. Associated to these main magnets, there is a great number (4 800) of smaller superconducting corrector magnets.

In the LSS there is a wide diversity of dipoles, quadrupoles and multipole correctors, with various functionalities: 86 quadrupoles, cooled at 4.5 K; 20 separation dipoles and 32 “inner triplet” quadrupoles

Fig. 1: the 8 LHC sectors, the 2 beams, the ARC and its cells

Proceedings of ICEC 22-ICMC 2008, edited by Ho-Myung CHANG et al. ⓒ 2009 The Korea Institute of Applied Superconductivity and Cryogenics 978-89-957138-2-2

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near the experiments, cooled at 1.9 K; 114 conventional warm dipoles and quadrupoles, in high radiation areas where the heat loads are too high for safe operation of superconducting magnets.

A cryogenic distribution Line (QRL), running alongside the magnets, feeds them with helium through jumper connections (every 107 m in the ARC). Scattered along the LHC circumference, 10 000 sensors and actuators are mounted either in the magnets or in the QRL.

At every IP, several electrical feed boxes (DFB) hold and cool the superconducting current leads, through which the magnets are powered; overall, 52 DFBs are equipped with 5 000 cryogenic instruments.

At P4, the two counter-rotating proton beams will each be accelerated up to 7 TeV, by 2x8 super-conducting RF (400 MHz) cavities (ACS), operating at 4.5 K, and including 200 cryogenic instruments.

HARDWARE

Fieldbuses As the cryogenic instruments are distributed over large distances, they are accessed by industrial field networks. These fieldbuses allow considerable simplification in cabling and maintenance, compared to classic point-to-point connections between process controllers and field devices; in addition, they offer the capability of remote diagnosis and configuration.

Whenever possible, the Cryogenic Distribution Control System (CDCS) is based on well-known [2] standard industrial equipment, like high-end S7® Programmable Logic Controllers (PLC) and Profibus® remote-IO stations, both from SiemensTM. Nevertheless, specific developments were necessary: 1. A large part of the front-end electronics has been designed at CERN [3], to include high-accuracy

signal conditioning for thermometry, and to be radiation tolerant (rad-tol) in order to cope with the high level of ionizing radiation in the LHC tunnel. Each sector has (Table 1) more than 100 rad-tol electronic crates, with WorldFIP® bus interfaces and signal conditioner cards for temperature, pressure, level sensors and for electrical heaters. Some 80% of the crates are evenly distributed, placed under the ARC and DS magnets, whereas the remainder is concentrated in radiation-protected areas (UA, UJ, RR) near the IPs, because they cannot withstand the radiation in the tunnel LSS.

2. Under CERN’s requirement, Siemens developed a version of their Profibus “intelligent” valve positioner [4] with its electronics, which is radiation sensitive, split from the valve pneumatic actuator. In each sector there are about 180 such positioners, grouped in 4 radiation-protected areas: 2 (UA, UJ) near the IPs and 2 (RE) in the ARC (Fig. 2).

TT CV PV QV PT LT EH total FIP

cratesFIP

segmentsProfibus segments PLC CCL

alarms interlocks

average / sector 1 000 325 90 90 65 310 1 880 100 8 5 2 2x250 600+500total all-sectors 8 000 2 600 720 720 520 2 480 15 040 800 68 42 16 4 000 8 800

Per sector, eight WorldFIP network segments (1 Mbit/s) access data from most of the thermometers

(TT), pressure sensors (PT), level gauges (LT), and digital inputs (like on-off valves end-switches or pressure switches), and convey the commands for electrical heaters (EH).

Also per sector, five Profibus network segments (1.5 Mbit/s) are used for the command of on-off valves (QV, PV), for the command and feedback of analog valves (CV) and of some heaters (EH), and to access “intelli-gent” instruments in general.

The commissioning of the hardware components has already been reported elsewhere [3, 5, 6, 7, 8].

Table 1: amount of instrumentation and control components

Fig. 2: Profibus and WorldFIP layout in tunnel and protected areas

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Controls Architecture As the Profibus protocol is seamlessly integrated with the Siemens PLCs, these communicate directly with the Profibus remote-IO stations and valve positioners, confined in protected areas. Conversely, the WorldFIP protocol is unintelligible for the Siemens PLCs; the WorldFIP-PLC communication gateway is provided by dedicated Front-End Computers (FECs) [9]; cycling at 500 ms, they perform data conversion to physical units, including the calculation of individual non-linear transfer functions.

Per sector, there are 2 PLCs (one for the ARC and DS and the other for both LSS); also cycling at 500 ms, they run some 250 Closed Control Loops (CCLs) and 500 alarms and interlocks. The CERN secured Ethernet Technical Network (TN) is used for the communication between the PLCs, the FECs, the SCADA, and with other systems’ PLCs and SCADA (Fig. 3).

The PLCs and FECs are installed in surface buildings, close to each of the 5 cryogenic plants (at P18, P2, P4, P6, P8), and are connected to the underground Profibus and WorldFIP equipment via optical fibers, signal repeaters and copper cables.

The man-machine interface is based on two SCADA systems (Supervisory Control and Data Acquisition), built with PVSS® and running on data-servers hosted in the CERN Control Center (CCC): 1. CRYO-SCADA, used by the operators to access data and commands relevant to the cryogenic process, comprises synoptic panels (that provide navigation, monitoring and control for all instruments), alarms and interlocks handling, real-time and historical trends, data and event logging and archiving (Fig. 4); 2. CIET (Cryogenic Instrumentation Expert Tool), used by the control experts to remotely monitor, configure, parameterize, and reset the WorldFIP read-out channels.

The PVSS data-servers are accessible all over the CERN site, via the TN, on clients locally running Human Machine Interfaces (HMI): Operator Work Stations (OWS) or Engineering Work Stations (EWS). The data-servers regularly send all data to long-term central storage (Logging) for off-line analysis.

Fig. 4: part of synoptic screen in CRYO-SCADA, showing two ARC cells fed from the QRL

Fig. 3: controls architecture

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Fig. 5: PLC code production cycle

SOFTWARE

Databases Because of the number and diversity of the cryogenic instrumentation, several databases (DBs) are intensively used to manage the characteristics and the relations of instruments; they are the knowledge source for front-end hardware (WorldFIP and Profibus) manufacturing, installation and test; moreover, the automated software production depends totally on information directly extracted from DBs. Furthermore, web interfaces offer human access to those DBs, to manually store or retrieve data.

The LHC Layout DB [10] manages the information on all LHC equipment topology, and logical or physical relationships; we have stored there the whole cryogenic instrumentation and controls infrastructure: cables, connectors, pin-outs, electronic modules, crates, racks, fieldbuses, and logical ins-trumentation channels; it can be directly accessed by the electronics manufacturer to configure the crates, by the test stations in the field, and by the automated generator of specifications for the control software.

The CERN Engineering and Equipment Data Management System (EDMS [11]) provides storage and management of all engineering documents and equipment information; the application MTF (Manufacturing and Test Folder [12]) is thoroughly used to store and track individual equipment data, comprising: calibrations, results of test measurements, status flags, and strict follow-up of the steps of manufacturing, assembly & test procedures.

Our Controls Layout DB provides an interface between MTF, LHC Layout DB, and Thermbase (the dedicated DB where we have loaded the calibration data, fitting functions and interpolation tables for all thermometers in the LHC). In addition to instruments data, Controls Layout also contains additional parameters such as instrument relations in control loops, PID coefficients, alarms and interlocks thresholds. We are currently developing Sensorbase DB, as an upgrade of Thermbase, in order to consistently gather all the metrological data of thermometers, pressure sensors and level gauges.

UNICOS baseline The control software (for FEC, PLC, CIET, and CRYO-SCADA) is mostly based on the CERN UNICOS framework (UNified Industrial COntrol System [13]), which provides methodology, components, and tools to design and program industrial control systems; it includes: base functions library (with modular PID algorithm), skeleton templates and code generators / replicators, which allow rapid prototyping of the control system while minimizing human intervention and error sources.

The information from the various DBs is combined in specific views of the Controls Layout DB (Fig. 5), to be easily accessed by the specifications generator that was built to produce files with: 1. hardware configuration for the PLCs and Profibus front-end; 2. Excel® tables for the code generators; grouped by UNICOS object type, these spreadsheets list all instrumentation channels, associated parameters, calibration IDs, and logical connections.

The specifications for one PLC contain 5 600 objects of 16 types. For each object, the UNICOS S7-Generator creates the memory assignment for PLCs and SCADA, the PLC source code for the objects and for the process logic, and the code for the PLC-SCADA communication middleware. The source code of a single PLC typically contains 250 000 lines of SCL (Structured Control Language); it is compiled together with the UNICOS Library; the machine code loaded in the PLC memory amounts to more than 3 MByte.

PLC code production After the development and commissioning of PLC code for

the first LHC sector, it became clear that the UNICOS baseline generators had to be adapted and extended to cover the singularities of the LHC machine, especially in the LSS [14]. An additional code generation tool handles process specificities not covered by the UNICOS generators, such as: data blocks for communication with external systems (700 variables per

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sector); logic for magnet powering interlocks (10 per sector, calculated from up to 250 signals, which now takes a few minutes to code instead of several days; logic for the process sequencer (Fig. 6); calculation of min/max/avg values for families of instruments (4 200 functions with up to 250 arguments).

The standard UNICOS validation tools did not cover the newly defined parameters, which had to be manually checked; many errors were found close to the end of source code generation or even later, during compilation or during operation; therefore, the production-verification-correction cycle could take several days. For the following sectors, a newly built specifications validation tool permitted to automatically check: communication variables, logic parameters, object dependencies, completeness of the data, and the integration of the LHC singularities; most errors could thus be discovered within an hour.

Based on the UNICOS skeleton, 140 logic templates were written for families of controllers, valves, heaters, and also for global logic, process sequencer, alarms & interlocks. Additionally, pieces of code that are common to several templates were replaced by calls to external functions with argument passing; modifications of process logic are thus faster to implement and less error-prone.

Before deployment in the production machines connected to the field, the project is loaded in a test PLC, with simulated instruments, for thorough tests by the process engineers.

The UNICOS automated checking and generation tools proved to be essential for flexible and robust PLC code generation; the additional tools that we developed improved the code reliability, by minimizing human mistakes, reduced the production cycle to 2 days, and simplified long term maintenance.

SCADA In every sector, the SCADA contains some 200 different panels, of which 40 contain synoptic

diagrams (Fig.4), 35 are bar-graphs, 35 concern the process sequencer (Fig.6), and 60 are dedicated to alarms and interlocks. Half of the synoptic panels are in the ARC and present similarities between themselves in one sector, and from one sector to another. We have created a few generic template panels with only static drawings and each one with a rather complex PVSS initialization script. Every time a panel is loaded on the HMI, its script reads a string of parameters with information of what instrument widgets to add to the panel, and where to position them, according to which ARC cell it corresponds. The different strings of parameters were previously created by a parameter generator, directly accessing the Layout and Controls DBs to know which instruments have to be visualized in a given panel.

Using this methodology of parameterizing repeated occurrences of similar screens, we have reduced by a 15 fold the number of different ARC panels in the whole LHC, thus dramatically shrinking the development time. Unfortunately, the panels of the tunnel LSS and of the DFBs are not repetitive and could not be parameterized; they have all been manually designed.

The instruments that are flagged in the DBs as not connected to the control system are automatically made invisible by the parameter generator, who just does not add them to the parameter string. Furthermore, when a damaged instrument must be removed from the panel, its reference can manually be deleted from the parameter string, until a new string generation can be automatically done from an updated DB.

In order to visualize the geographical profile of physical variables, each sector needs 35 bar-graph panels; they are also based on a very small number of template panels, with a script to read the parameters containing the names of variables to be plotted. The same bar-graph templates are used in all sectors, in conjunction with the appropriate set of parameters.

Likewise, the visualization in CIET of the contents of the individual FIP crates is based on one single template and 800 different strings of parameters.

Perl® scripts were developed to convert panels from CRYO-SCADA to CIET; because, although the static graphics are the same, variable names are slightly different between the two systems; these scripts are used to copy and convert fixed synoptic panels, parameterized synoptic panels or bar-graph panels. The parameter generator has also been extended to CIET crates, synoptics and bar-graphs.

Fig. 6: command panel for sequencer

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All these tools and generators have been integrated in a Panels Maintenance Framework (PMF), from which can also be launched the PVSS HMI and Graphical Editor. Moreover, many dedicated PVSS scripts were written for easy application repetitive operation commands to families of SCADA objects.

CONCLUSIONS

The control software production relies on a set of databases and on a package of automatic generation tools, which have been developed to create data and code in several steps, according to a well established methodology.

By the end of 2007, two sectors have successfully reached nominal conditions and passed several magnet powering tests [15]. The software production cycle had then to be reviewed, in order to cope with the tight schedule required for the following sectors; applying extra effort on automatic code production and check, we managed to reach a rate of 1 new sector every 2 weeks, while in parallel giving support and performing modifications on sectors already in operation.

The Closed Control Loops performance depends on the quality of Ethernet communications between PLCs and Front-End Computers; thanks to the low network occupancy, the high availability of the Technical Network infrastructure, and the effort put in topology optimization, the controls performance is not hampered by the fact that Ethernet is not a deterministic network like the fieldbuses.

All eight sectors are now cold and they are expected to reach nominal temperature and magnet current this summer, ready for the first particle injections. The operational performance, within specifications, of the different instrumentation channels before cool-down has exceeded 95% for thermometers (and about 100% for other instruments) for the 3 first sectors. [6, 7]

The experience gained with the past LHC-String projects [2] has set a valuable ground for the definition of the hardware & software architectures, and of the procedures for building and testing them.

We wish to express our gratitude to the colleagues from industrial support and from the collaborating Institutes, for their motivation and professionalism – without them, this venture would have never been possible; acknowledgements also to Prof. Evangelos Gazis from NTU-Athens, to Dr. Jan Kulka from AGH-Kraków, and to Dr. Roberto Saban from CERN, who put in place the Hardware Commissioning Collaboration; and finally to the cryogenic operation team, for their help in the commissioning and for their patience while waiting for our improvements or repairs.

REFERENCES

1. Brüning O et al, LHC design report Vol. I, CERN-2004-003 (2004) 2. Gomes P et al, Experience with the String2 Cryogenic Instrumentation and Control System, ICEC20, Beijing, China (2004) 3. Vauthier N et al, First Experience with the LHC Cryogenic Instrumentation, CEC-ICMC2007, Chattanooga, USA, (2007) 4. SIEMENS, Electropneumatic Positioner with external Operating and Control unit, SIPART PS2 PA, 6DR59xx (2004) 5. Fluder C et al, Experience in Configuration, Implementation and Commissioning of a Large Scale Control System, ICCC2008, Sinaia, Romania (2008) 6. Penacoba G et al, Outcome of the Commissioning of the Readout and Actuation Channels for the Cryogenics of the LHC, EPAC08, Genoa, Italy (2008) 7. Lopez A et al, Quality Assurance of LHC Cryogenic Instrumentation at Installation and Commissioning: Practical Experience, ICEC22, Seoul, Korea (2008) 8. Avramidou R et al, The commissioning of the instrumentation for the LHC tunnel cryogenics, IEEE NSS-MIC 2007, Honolulu, Hawaii, USA (2007) 9. Blanco E et al, LHC Cryogenics Control System: Integration of the Industrial Controls (UNICOS) and Front-End Software Architecture (FESA) Applications, ICALEPCS07, Knoxville, Tennessee, USA (2007) 10. Le Roux P et al, The LHC Functional Layout Database as Foundation of the Controls System, ICALEPCS07, Knoxville, Tennessee, USA (2007) 11. Boyer T et al, The CERN EDMS An Engineering and Equipment Data Management System, EPAC02, Paris, France (2002) 12. Delamare C et al, Manufacturing and Test Folder: MTF, EPAC02, Paris, France (2002) 13. Gayet Ph et al, UNICOS a Framework to Build Industry-like Control Systems Principles Methodology, ICALEPCS05, Geneva, Switzerland (2005) 14. Fluder C et al, An Automatic Approach to PLC Programming for a Large Scale Slow Control System, ICCC2008, Sinaia, Romania (2008) 15. Serio L et al, Validation and Performance of the LHC Cryogenic System through Commissioning of the First Sector, CEC-ICMC2007, Chattanooga, USA, (2007)

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ICE22-ICMC2008 - Seoul, Korea, July 21-25, 2008Main ScreenTitleContents PrefaceICE Committee Members and ICMC Board MembersLocal Organizing Committee MembersSponsors and ExhibitorsConference SnapsSPECIAL SESSION,“100 YEARS OF LIQUID HELIUM”Heike Kamerlingh Onnes and the Road to Liquid HeliumHelium liquefaction and refrigeration since 100 yearsSub-Kelvin technology towards absolute zeroHelium: Past, Present & Rising FutureA Perspective on Key Market Issues from an Industry Leader

PLENARY SESSIONThe Cryogenic System of KSTAR, a Superconducting TokamakPresent status and future trends of high temperature superconductor power applications in JapanWHAT "NORMAL" REFRIGERATION CAN LEARN FROM CRYOGENICS (MENDELSSOHNAWARD LECTURE)

LARGE SCALE REFRIGERATIONS 900-L liquid xenon cryogenic system operation for the MEG experimentCryogenic operation methodology and cryogen management at CERN over the last 15 yearsUSING DYNAMIC SIMULATION TO SUPPORT HELIUM REFRIGERATOR PROCESSENGINEERINGThe control system for the cryogenics in the LHC tunnelCharacteristic Tests of a 1600W- class Refrigeration System at 10K to 70KExperimental validation of the thermal performance of the 1.9 K magnet cryostats during thecommissioning of the LHC

J-T, G-M AND STIRLING CRYOCOOLERSReliability of Stirling cryocooler with gas bearing systemA simple method of temperature smoothing for a 4 K Gifford-McMahon refrigeratorPerformance Realization of Single Stage Stirling Cryocooler at ISROImprovements of the mechanical coolers operating below 4.5 K for space useUltra-Low Vibration Cryogenic Refrigerator for “Dry Cooling” Technology

PULSE TUBE CRYOCOOLERSExperiments on a pulse tube refrigerator with an orifice inertance or a lumped-boost configurationA 4 K single-stage Stirling type pulse tube cryocooler precooled by G-M type pulse tube cryocoolerTests of Four PT-415 Coolers Installed in the Drop-in ModOn-Demand LOX & LN2 By On-Site Acoustic Liquefiers20K Pulse Tube Cryocooler for space applicationsDevelopments on a wide range of coaxial Pulse-Tube Refrigerators at THALES CryogenicsHigh Frequency Pulse Tube Driven By a Miniature Thermoacoustic EngineCFD simulation of fluid flow and heat transfer in high frequency pulse tube refrigeratorsInvestigations of two-stage pulse tube cryocooler operating down to 2.5 KInvestigation on a single-stage coaxial pulse tube cryocooler for small particle detectors at CERNOSCILLATING FLOW CHARACTERISTICS OF ELEMENTS IN A PULSE TUBE COOLERLateral motion of the cold stage in a pulse tube cryocooler with self-cancellation methodNumerical Simulation of the High-Frequency Miniature Pulse Tube Refrigerator with TaperedRegeneratorInvestigation of two-stage high frequency pulse tube cryocooler with precoolingExperimental investigation of a thermal-coupled two-stage pulse tube refrigeratorExperimental investigation on the onset temperature gradient using the multifunction cascadethermoacoustic deviceAnalysis of a vibration reduction system for pulse-tube cryocoolerIdentification of Vibration Sources in Pulse Tube Cryogenic CoolerVibration Control of a Pulse Tube Cryogenic Cooler in Vibration-SensitiveInstrumentation

GAS SEPARATION AND LIQUEFACTIONCryogenic removing of carbon dioxide in small natural gas liquefaction systemLarge-scale hydrogen separation from coke-oven gasDynamic characteristics of single stage mixed-refrigerant natural gas liquefaction processAnalysis on distillation column in low concentration CMM liquefaction systemDESCRIPTION OF A SYSTEM DESIGNED BY AIR LIQUIDE DTA AND DEDICATED TOTHE RECOVERY AND RE-CONDENSATION OF LIQUID HELIUM CONTAINERSPERMANENT BOIL-OFFEVOLUTION OF THE STANDARD HELIUM LIQUEFIER RANGEDESIGNED BY AIR LIQUIDEAdaptation of advanced control to the helium liquefier with C-PRESTA simulation study for the virtual commissioning of the CERN central helium liquefier

CRYOGENIC FLUIDSFlow characteristics of slush nitrogen in various types of pipesA 3-D model of superfluid helium suitable for numerical analysisSuperfluid Turbulent Flow Characteristics of Thermal Counterflow Jet Measured by PIVCavitation Feature of He II Flow Through a Venturi ChannelOn the viscosities of the quantum fluid helium by molecular dynamics simulationThe thermal conductivity of liquid helium-3THE RAS LAFFAN HELIUM RECOVERY PLANT

HEAT TRANSFERThermal behaviors of Rutherford type stack of cables with polyimide isolation in normal andsupercritical heliumVisual observation of the superheated state of He II in narrow two-dimensional channelEffects of Location and Influx Angle of Precooling Return Flow on Thermal Stratification in LiquidOxygen Tank of RocketOvercoming Slowly-developing Maldistributions in Horizontal Heat ExchangersExperimental study of film boiling in helium natural convection boiling flowAdvanced cryogenics cooling technique using metal porous media with liquid nitrogenShould cryogenic heat exchangers be operated in a vertical or an horizontal position?Heat transfer characteristics related to the superheatingin two-dimensional channels in He IIInvestigation on heat transfer performance of a vertical wickless heat pipe at cryogenictemperatureHeat transfer and pressure drop reduction of slush nitrogen in a turbulent pipe flowForced convection heat transfer to supercritical fluidsPressure drop and temperature rise in He II forced flow through an orifice plateVapor behavior around a thin wire during film boiling in He II under atmospheric down to saturated vapor pressure conditionVisualization study of film boiling in saturated He II under low gravity environmentForced convection heat transfer of nitrogen at supercritical pressureExperiments and 3-D numerical analyses for heat transfer from a flat plate in a duct withcontractions filled with liquid He IINumerical Simulation of Upward Subcooled Boiling Flow of Refrigerant-113 in a VerticalConcentric AnnulusMulti-phase CFD Analysis of Cryogenic Cavitating Flows through Elbow PipeNumerical simulation of thermal convective instability in helium at supercritical pressures

INSTRUMENTATION AND PROCESS CONTROLElectronic Instrumentation for Multiplexing Palladium based hydrogen gas sensorsModular data acquisition system for cryogenicsNumerical simulation of a superconducting level sensor for liquid hydrogen with MgB2 wireCalibration of capacitance type cryogenic liquid level sensor using discrete array type liquid levelindicatorEvaluation of temperature distribution of multi-layer insulations using Fiber Bragg GratingsensorsThe demonstration of active magnetic regeneration (AMR) using gadolinium and gadolinium alloyfor the magnetic materialQuality assurance of LHC cryogenic instrumentation during installation and commissioningAn Adiabatic Calorimeter Based on a Closed-Cycle Refrigerator for High-Accuracy ThermometerCalibrations Between 13 K and 84 KSmart sensors at temperatures down to 77 KOptical system for cryogenic liquid level measurements in small volumesInvestigations on fiber Bragg cryogenic temperature sensorsComparison of TVO – and Cernox temperature sensorsThe upgrade of the control system for the CERN/NA62 liquid krypton detector

CRYOSTATS AND INSULATIONHeat leak measurement on zinc-coated cryogenic pipe for superconducting power transmission linePerformance of the Cryostat for a Prototype ILC DC Combined Function SuperconductingQuadrupole-Dipole MagnetThe Impact Of Directional Emissivities On The Heat Transfer Between Cryogenic AluminiumSurfaces Down To Liquid Helium TemperaturesThe effects of compression on heat transfer through fibrous insulation materials over thetemperature range +20°C to -160°CThermal radiation through a metal pipe and its reductionCryogenic setup for Q-factor measurements on bulk materials for future gravitational wavedetectors

NEW DEVICES AND NOVEL CONCEPTSDynamic Simulation of a 1.8K Refrigeration Unit for the LHCStudy on a regenerator utilizing multi-temperature heat sources in a thermoacoustic engineExperimental design and simulation of offloading system for LNG-FPSOSuperSuburb – A Future Cryo-powered Residential CommunityDevelopment of miniature co-axial pulse tube cryocooler with novel integral cold fingerRadiation analysis of anti-Stokes fluorescent cryocooler with network-matrix methodA single-stage GM-type pulse tube cryocooler reached 10 KA Rapid Vent System of Liquid-Nitrogen CryostatSeries assembly of cryogenic lines in confined environment by orbital welding.The correlation two-phase flow meterA CLOSED CYCLE HELIUM SORPTION PUMP SYSTEM AND ITS USE IN MAKINGHYPERPOLARIZED COMPOUNDS FOR MRI IMAGINGImpedance modulation of linear generator on the coaxial traveling-wave thermoacoustic engineAn Efficient Helium Sorption Pump in the 1 K Temperature Range with a Small Footprint

FUSIONConceptual design of the cryogenic system for ITERReview of conceptual design of ITER cryoplant systemDevelopment of the Cryogenic Circuit Conductor and Coil (4C) Code for thermal-hydraulicmodelling of ITER superconducting coils.Cryoline for torus and cryostat cryopumps of ITER: the engineering design pathwayEstablishment of investigation process on neutron irradiation effect of superconducting magnetmaterials for fusionDesign, construction and performances of the KSTAR Helium Refrigeration SystemThermohydraulic studies related to pulsed heat loads generated by JT60-SA tokamakControl interface between W7-X control systems and helium refrigeratorProgress Report of the Cryo-Plants for Wendelstein-7XThe commissioning results of the warm compression system for the KSTAR helium refrigerationsystemPreparing the test facility TIMO-2 for the acceptance tests with the ITER torus cryopumpHaas, H.*,Thermohydraulic analysis for the ITER superconducting coilsCommissioning results of the KSTAR helium refrigeration system

ACCELERATORSTEST STAND FOR TESTING XFEL MAGNETSAnalysis for liquid cryogen spillage in the superconducting cyclotron building at VECCThe Status of Cryogenic System Design for Taiwan Photon SourceDesign of the cryogenic system for SSRFThermal analysis of UHV beam tube of SIS100 for FAIRPerformance test of a helium refrigerator for the cryogenic hydrogen system in J-PARCCommissioning of the cryogenic hydrogen system in J-PARC: first cool-down operation withheliumEXPERIMENTAL TESTS OF FAULT CONDITIONS DURING THE CRYOGENICOPERATION OF A XFEL PROTOTYPE CRYOMODULECryogenic distribution for radioactive secondary beam fragment separator (Super-FRS) of FAIRA cryogen free magnesium diboride dipole magnetCommissioning of the cryogenic hydrogen system in J-PARC: Preliminary operation by helium gasCryogenic system for VECC K500 superconducting cyclotronSUMMARY AND RESULTS OF THE CRYOPLANT OPERATION FOR HERACold electrical connection for FAIR/ SIS100Commissioning of the Cryogenic Plant for the Cryogenic Storage Ring (CSR) at Heidelberg

SPACE CRYOGENICSMilligravity flight experiments of a continuous ADRComparison of two empirical cryocooler modelsAIR LIQUIDE SPACE PULSE TUBE CRYOCOOLERS AND ASSOCIATED COOLER DRIVEELECTRONICSDesign principles and operational results of the cryogenic system for the ATLAS liquid argoncalorimeter50 mK continuous cooling for space by a pre cooled demagnetization refrigeratorEXPERIMENTAL STUDIES OF THE EFFECT OF CRYOGENIC TREATMENT ONRESIDUAL STRESSES IN INTEGRAL DIAPHRAGM PRESSURE TRANSDUCERS FORSPACE APPLICATIONS

SUPERCONDUCTNG MAGNETInfluence of mass flow on the upgraded cooling system for the LHD helical coilsOperation and control of cold compressors in subcooling system for LHD helical coilsConduction cooling system for superconducting magnet using a two-stage cryocoolerMeasurements of heat transfer through Rutherford superconducting cable with different electricalinsulation wrapping schemesFirst cool-down and test at 4.5 K of the ATLAS superconducting magnet systemassembled in the LHC experimental cavernCryogenic heat load and refrigeration capacity management at the Large Hadron Collider (LHC)CRYOGENIC MAGNET TEST FACILITY FOR FAIR

LTS APPLICATIONSSummary report on the cryogenics summer school in these ten yearsTowards beyond-1 GHz NMR: Field stabilization and NMR measurement in the external currentmodeAC Loss Analysis on Superconducting Coupling Solenoid in MICEPressure Drop Measurements In Cable-In-Conduit Conductors(CICC) With Different LayoutsThin cryogenic X-ray windows

HTS APPLICATIONSThermal Isolation for Fiber-Based Microcryocooler for HTS Electronics*AC loss of a tri-axial HTS cable composed of 2 layers per phase with balanced and homogenouscurrent distributionBi-2223 superconducting magnet working in sub cooled liquid nitrogenVibration isolation characteristics in magnetic levitation type seismic isolation device composed ofHTS bulk and permanent magnet2nd generation HTS wire hybrid superconducting magnet systemThe 30 m HTS power cable development and test

LOW-TEMPERATURE SUPERCONDUCTORSRECENT RESULTS OF R&D ON ITER RELEVANT NbTi AND Nb3Sn STRANDS IN BOCHVARINSTITUTENew model to study the influence of cabling pattern, magnet field profile and joint properties onshort sample qualification tests of ITER CICCsProgress and Status of Multifilamentary Nb3Sn Strands Fabricatedby Internal-tin Process for ITER in ChinaProgress on an innovative insulation technique for Nb3Sn wind & react coilsFabrication and characterization of Nb/Al and Ta/Al superconducting tunnel junctionsEffects of tin distribution in internal tin processed Nb3Sn strandFilament fracture and irreversible performance degradation in bronze and internal tin ITER typeNb3Sn strands

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Experimental studies of the effect of Cryogenic Treatment on residual stresses in Integral Diaphragm Pressure Transducers for space applications

Nadig D.S. +, Jacob S. +, Karunanithi R. +, Subramanian D.*, Prasad M.V.N.*, Geetha Sen*

+Centre for Cryogenic Technology, Indian Institute of Science, Bangalore – 560 012, India

*Liquid Propulsion System Centre, ISRO, Bangalore, India

Any machined component is develops residual stresses during machining and heat treatment. In many cases, the presences of these induced residual stresses are seriously detrimental for the functional reliability of the system. In this study, a cryotreatment system is designed and developed to reduce the residual stresses induced within the integral diaphragm of the pressure transducers during machining. These pressure transducers machined out of precipitation-hardened stainless steel were cryotreated for 24 hours at 98K. The residual stress results of cryotreated transducers indicated significant reduction. These reductions have reduced the problems of zero shift of the outputs of transducers.

INTRODUCTION

The practice of cryogenic treatment on metals has been extensively employed since many years mainly for improving life of cutting tools. While the results of cryotreatment on cutting tools have been encouraging, there is still large scope for research to study the effect of cryogenic treatment in the areas of improving dimensional stability of machined parts and gauges, removal of residual stresses, conversion of Retained Austenite to Martensite in steels etc. The effects of Cryotreatment to reduce the residual stresses of Internal Diaphragm Pressure Transducers used for measurement of propellant pressures are discussed in this paper.

A typical Cryo treatment cycle involves mainly involves 3 phases where the metal samples are cooled gradually to cryogenic temperature (cooling period), holding for extended length of time (soak time) and gradual warming (warming time) to room temperature. In normal practice a complete cryotreatment cycle takes around 36 hours with 5 hours of cooling, 24 hours of soaking and 7 hours of warming. These parameters can be modified for optimized results.

Figure 1 Cryo-Treatment Cycle

When metals are gradually cooled to cryogenic temperatures, soaked for a prolonged period and warmed to room temperature at a predetermined rate, the lattice structure of the atoms change due to stresses being relieved during cryogenic treatment cycle. In the case of ferrous metals, the soft, ductile, FCC structured austenite gets converted to strong and harder BCT structured martensite. Apart from these changes, the precipitation of newly formed carbides dispersed uniformly in the hard martensite structure induces a dense lattice structure.

In the present work, the effects of cryogenic treatment on Integral Diaphragm Pressure Transducers (IDLV) used for launch vehicles are carried out. These pressure transducers machined from Precipitation Hardened Martensite Stainless Steel (APX4, Carbon - 0.06%, Cr-16%, Ni-4% and Mo-1%) are used for measurement of propellant pressures. In the pressure transducer (Figure 2), propellant pressure is applied on one side of the diaphragm and strain gauges are bonded on the other side. Due to the applied pressure, the diaphragm deflects and induces proportional strain in the gauges which produce electrical out put. These electrical outputs are calibrated in pressure units.

Input pressure

Figure 2 Integral Diaphragm Pressure Transducer (IDLV)

Ideally, the pressure transducer outputs should obey linearity for all the values of input pressures exhibiting zero output pressure for no input. Apart from this the transducer output readings are expected to exhibit linearity over the entire range. The transducers have to be dimensionally stable for its useful life for total reliability. However, in the realization of these integral diaphragms from the raw material stage, stresses are induced during machining. If these induced stresses are not removed before final assembly, they will induce residual strains in the diaphragm. These strains in the diaphragm can cause drift in the output while functioning and the transducer performance will be unreliable.

Residual stresses in machined components are essentially locked up stresses induced in side the material during various stages of machining. These stresses in turn induce residual strains which are spread all over the component. These stresses can cause decrease in strength and durability. Stress boundary areas are more susceptible to micro cracking which can lead to premature fatigue and even failure. These stresses induce strains inside the component and can cause premature failure. Cryogenic treatment has been found very effective in releasing these residual stresses.

The main advantage of Cryotreatment on metals is known to be removal of stresses due to realignment of crystal structure. With a view to reduce the internal stresses in the diaphragm, it was planned to cryo treat the material from the raw material stage to the final stage, after each stage of machining with the following action plan.

STEP 1: Evaluation the initial properties of the raw material viz. Ultimate tensile strength, Yield strength, Percentage elongation, Hardness, Austenite content and residual stress level.

STEP 2: Cryo treatment of the raw material.(CT1)

STEP 3.Evaluation of the properties of the cryo treated samples and analysis.

STEP 4: Rough machining the raw material to remove 90% of the material.

STEP 5: Residual stress and hardness measurement

STEP 6: Cryo treatment (CT2)


STEP 8: Final machining of the material



STEP 11:Residual stress measurement

It was planned to cryo treat all the samples with cool down time of 8 hours, soak time of 24 hours at 98K and warm up time of 12 hours. It was planned to evaluate residual stresses, and retained austenite using X- ray diffraction techniques.

CRYOGENIC TREATMENT SYSTEM

The cryotreatment system incorporates mainly the cryotreatment chamber and an auxiliary LN2 supply system to supply controlled quantity of LN2 to the chamber to maintain the rate of cooling, soaking and warm up. The controlled LN2 supply to the chamber is carried out by using a solenoid valve activated by a PID controller. (Figure 3)

Figure 3 Schematic of the cryotreatment system

The cryotreatment unit is made of stainless steel with polyurethane foam (PUF) insulation. It has a fan-motor assembly mounted centrally in the top cover. The samples housed in the meshed trays are gradually cooled to cryogenic temperature by the cold nitrogen gas forced convection continuously produced by the rotating fan housed below the buffer tank containing LN2 and the cold exchange from LN2 circulating in the copper tube heat exchanger brazed on the outer wall of the metallic shroud housed around the meshed trays.

The LN2 supply is regulated by a solenoid valve operated by a PID controller with predetermined set points. Various cryotreatment cycles can be programmed to suit the requirements. The temperatures of the specimens are measured using Platinum Resistance Temperature Detectors (RTD). The temperature data of the samples read by PID over the period of the cryotreatment cycle are stored continuously using a data acquisition system.

Figure 4 Photograph of the cryo treatment system

The samples were cryotreated for a total duration of the 45 hours, which included 9 hours of cooling, 24 hours of soaking and 12 hours of warming to room temperature. The PID controller was programmed as per the preset conditions of temperature and time. The system was maintained at a low temperature of 98 K for 24 hours and specimens were allowed to warm up to ambient temperature by closing LN2 supply.

The residual stresses and retained austenite levels were evaluated using X ray Diffraction techniques.

RESULTS AND DISCUSSIONS

The cryotreatment was carried out after each stage of machining from the raw material stage to the final product and residual stresses were evaluated at each stage as shown in the tabular column (Table 1). It was evident that after each stage of machining, the stress level increased and this could be brought down by cryotreatment. The final machined diaphragm had residual stress level much less than the raw material and this could be further reduced by increasing the duration of cryo treatment (36 hours).

Table 1 Residual stress levels during various stages of cryotreatment (CT) of the diaphragm.

Stage

Raw material

CT-1

Rough

machining

CT-2

Final machining

CT-3

CT for 36 hours

Residual stress (MPa)

-535

-372

-497

-338

-363

-336

-308

The cryotreated pressure transducers have yielded very encouraging results. Hysterisis effects could be reduced considerably by nearly 20% which promised long term stability. Additional proof pressure cycling for 20 cycles further stabilized the hysterisis loop. The produced stable Martensite limit deformation of the diaphragm with time and hence dimensional stability. These positive effects could improve the overall reliability of the transducer considerably.

CONCLUSIONS

From the results it can be clearly seen that cryotreatment significantly reduces residual stresses induced during each stage of machining. Residual stresses can be considerably reduced further by cryotreating the samples for extended duration of time for 36 hours. There is still scope for optimizing the experimental parameters to obtain better results. Tempering effects can be studied after cryotreatment.

REFERENCES

1. Barron R.F., Cryogenic treatment of metals to improve wear resistance, Cryogenics, (1982), 22, 409-413

2. ”Metallography and microstructures- wrought Stainless Steel”, ASM International Materials,(1995),Vol 9

3. B.D.Cullity, “Elements of X ray diffraction”, Addison Wesley Publishing Co Inc, (1978)

4. “Heat Treating”, ASM Metals Hand Book , 1995, Vol 4

5. “Ioan Alexandru, Hand book of Residual Stresses, ASM Internatioanl ,2002

� EMBED Unknown ��

PAGE

6

_1256635111.unknown






INTRODUCTION






Input pressure




























Stage

Raw material

CT-1

Rough

machining

CT-2

Final machining

CT-3

CT for 36 hours


-535

-372

-497

-338

-363

-336

-308


CONCLUSIONS


REFERENCES







PAGE

6

_1256635111.unknown






INTRODUCTION






Input pressure




























Stage

Raw material

CT-1

Rough

machining

CT-2

Final machining

CT-3

CT for 36 hours


-535

-372

-497

-338

-363

-336

-308


CONCLUSIONS


REFERENCES







PAGE

6

_1256635111.unknown

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