As one of the activities of the US-LHC Accelerator Project, BNL is testing short samples of superconducting cables that will be used in the main LHC dipoles and quadrupoles. The purpose of these tests is to verify that the reels of superconducting cables as supplied by the vendors meet the required critical current specifications. The short- sample testing facility and the computer-assisted testing techniques for acquiring the data are described. We also describe the data analysis, data storage, and data transmission methods. (2 refs)

Ghosh, A

Jain, A

McChesney, D

Thomas, R

CERN Document Server

________________________*Work supported by the U. S. Department of Energy, ContractNo. DE AC02-98CH10886.#Email: thomas1@bnl.govTESTING AND EVALUATION OF SUPERCONDUCTING CABLESFOR THE LHC*R. Thomas#, A. Ghosh, D. McChesney, and A. Jain, BNL, Upton, NYAbstractAs one of the activities of the US-LHC AcceleratorProject, BNL is testing short samples of superconductingcables that will be used in the main LHC dipoles andquadrupoles. The purpose of these tests is to verify thatthe reels of superconducting cables as supplied by thevendors meet the required critical current specifications.The short-sample testing facility and the computer-assistedtesting techniques for acquiring the data will be described.We also describe the data analysis, data storage, and datatransmission methods.1 APPROACHElectrical tests of cable samples must be done duringcable production so that cable manufacturing problemsmay be detected as early as possible. During the periodthat CERN is procuring superconductor cable for the LHCproject, BNL is providing resources to verify the super-conducting properties of the cables. The BNL short-sampletest facility is used to measure the critical current, Ict, ofshort (≤1 meter) samples of LHC dipole and quadrupolecables.The number of tests that must be performed is set bythe cable production schedule and reaches a peak rate ofabout 20 samples per week. The total number of tests thatwill be performed over the six-years of the collaborativeeffort will exceed 3000.A large quantity of information needs to be acquired,analyzed, and stored. Also, reports on individual runs,summary sample reports, and compatible raw data filesmust be regularly transferred to CERN. Because the datahandling tasks themselves present the largest challenges,the database is the key organizing structure for all otheroperations.This approach is possible as a result of recentadvances in networked databases and distributed object-oriented software programming. These allow softwareprograms located anywhere on a network (either a localintranet or the world-wide Internet) to interact with adatabase using the client/server model.As samples are received, information about eachsample is entered into a table (CableTrack) in the data-base. When an assembly of four samples is placed in asample holder for testing, information about the assemblyis entered into the CableAssembly table.When the actual testing takes place, the data acquisi-tion program interacts directly with the same database togive the user a drop-down list of assemblies from whichhe selects the assembly being tested. From that selectionalone, the data acquisition program can obtain informationfrom the remote database regarding the physical character-istics of the samples being tested and their instrumentationwiring. Fig. 1 shows the data flow and database interac-tions.Figure 1. Selected tables of the Cable Database andinteractions with the data flow events.When data are acquired, values are written into theCableWave table of the database describing the experi-mental conditions and, the name of the raw binary datafile (a copy of which is automatically placed on thenetwork file server).Once this information has been obtained, dataanalysis can be carried out on any machine connected tothe network. (Software has been produced that loads datainto workbooks, fits the data to a model, and writes resultsback into the CableAnalysis table of the database.) Otherprograms allow the user to select records from the Cable-Analysis table which the program then uses to producesummary reports.0-7803-5573-3/99/$10.00@1999 IEEE. 3188Proceedings of the 1999 Particle Accelerator Conference, New York, 1999Figure 2. Sample arrangementin the sample holder. Figure 3. User form for entering run information .Figure 4. Actual signals for low-noise conditions.Finally, result files, plain-text raw data files, sum-mary reports are shipped to CERN using ftp (file transferprotocol). Although there is a program to assist in thisstep, it has not yet been fully automated. Also, the con-struction of a web page that allows those at CERN tofollow the status of any sample is still under development.2 SHORT SAMPLE TEST FACILITYThe standard tests are performed at 4.2 K. Approxi-mately 10% of the cable samples are being tested insuperfluid helium at 1.9 K to determine the consistency ofthe ∆H shift of the Ict vs. H curve from 4.2 K to 1.9 K.Four samples can be tested in one cool-down of a singletest station (cryostat), so two additional test stations arebeing built to meet the LHC production schedule.The layout of the four samples in the sample holderis shown in Fig. 2. The sample holder is placed in acryostat which also holds a superconducting dipole magnetwhich can produce fields as high as ∼9 T at 1.9 K [1].The magnet is energized by a 8.5 kA power supply; asuperconducting switchallows it to operate in thepersistent mode.As the critical currentof the cable will generallybe in the range of 10–20kA, two 15 kA suppliesare operated in parallel tosupply the cable test cur-rent.In addition to thepower supplies and theircontrols and safety devices(quench detectors and fault detection circuits), the facilityincludes the instrumentation necessary for controlling thecryogenic environment and for measuring the criticalcurrent of the samples under test.Two computer systems are used: 1) a cryogenicsystem that monitors liquid helium levels, temperatures,and pressures and both sets and monitors the flow ofhelium through the gas-cooled leads, and 2) an experimen-tal system for controlling the sample power supply, takingdata, and storing data in the SQL database.3 TESTThe goal of the short-sample cable tests is to deter-mine the transport critical current of the samples. Thiscritical current is a function of temperature and themagnetic field. In order to obtain standardized results fora specified reference temperature and reference field, rawdata must be obtained for several applied fields with thesamples at the temperature of the helium bath; that is, oneacquires a set of critical currents, Ic, at bath temperatures,Tb, and applied fields, Ba, for each sample.By pairing samples which are believed to havesimilar properties, it is possible to acquire data on twosamples simultaneously. Also, as there are three gas-cooled leads connecting the two sample pairs to thesample power supplies (see Fig. 2), four samples can betested in a single cool-down, with the pairs being testedsequentially.To acquire the Ic data, the operator first sets thecurrent in the dipole magnet for the desired applied field,then connects the sample power supply to the first samplepair to be tested. He then enters the required informationinto the data acquisition program regarding the ramp rateand maximum current for the ramp on the form shown inFig. 3.Three high-resolution volt meters are triggeredsimultaneously as the current is ramped to obtain thevoltage drops across the two samples and the current levelas a function of time, as shown in Fig. 4.3189Proceedings of the 1999 Particle Accelerator Conference, New York, 1999Figure 5. Noisy data and model fit results.Figure 6. Linear fit to experimental Ict results.Several sets of data are obtained at different dipolefield levels for each sample pair.4 ANALYSIS AND REPORTINGOnce the raw data have been collected, analysis canbegin on any workstation connected to the network, sinceall the required information for each run can be extractedfrom the database. On many occasions there is consider-able electrical noise visible on the signals, primarily as aresult of phase and voltage flicker that is produced by thesynchrotron accelerators located nearby. When this is thecase, the use of a model and a fitting procedure allow thevalue of Ic to be extracted. (See Fig. 5.)The results of the analyses are automatically storedin the database. The reporting application then extracts thisinformation, converts the Ic values to Ict’s (the criticalcurrent at the specified reference temperature, Tref), andcomputes the peak field, H, experienced by the sample(the sum of the applied field and the self-field [2]). Thenthe program performs a linear fit to the Ict(H) values tocalculate Ict at the reference field. See Fig. 6.Other programs access the database to create plain-text files of results and reports and then transfer these toCERN. A web-based status page is under developmentwhich will always be current, since it uses Active ServerPage technology to obtain information directly from thedatabase whenever the page is accessed.5 SUMMARY AND CONCLUSIONSOur experience to date indicates that a database-centered approach to this data intensive cooperativeprogram is both practical and feasible. The state ofdevelopment of commercial operating system componentsfor distributed applications, software development lan-guage tools, data analysis applications, and databaseservers is sufficiently mature that users can develop andmaintain sophisticated client/server applications.Using the database as the organizing structure aroundwhich software is developed for carrying out the manytasks of the collaborative effort unifies all the elements ofthe process and makes it possible for the users to have acomprehensive understanding of the state of the project.The principal disadvantage is that this approachrequires a rather complete understanding of what kinds ofinformation are to be collected. If there has already beenconsiderable experience with the procedures that need tobe carried out and the difficulties that can possibly arise inacquiring and entering the data, then this approach isespecially appropriate. If, on the other hand, there aremany unknowns regarding what data it is necessary tocollect and what difficulties may occur in collecting thedata, a database-centered architecture may be less useful.As all the applications depend on the database tables, if itis necessary to frequently change the structures of thesetables during the initial stages of the project to satisfy therequirements of one or another of the applications, thesechanges have a cascading effect and may require that otherapplications be updated.However, this is not a fault of the database-centeredapproach itself, but merely an indication of the inter-relatedness of the various tasks.In general this data-driven method is unsuited fornew exploratory investigations of an open-ended nature,but is well suited for organizing repetitive experimentaland reporting procedures of a known complexity.6 ACKNOWLEDGMENTSThe authors wish to thank A. Verweij and L. Obeli(CERN) for useful discussions.7 REFERENCES[1] R. McClusky, K. E. Robins, and W. B. Sampson, “A Nb3Sn HighField Dipole,” IEEE Trans. On Magnetics, Vol. 27, p. 1993 (1991).[2] M. Garber, et. al., “The Effect of Self-Field on the Critical CurrentDetermination of Multifilamentary Superconductors,” IEEE Trans.onMagnetics, Vol. 25, p. 1940 (1989).3190Proceedings of the 1999 Particle Accelerator Conference, New York, 1999

Testing and evaluation of superconducting cables for the LHC

As one of the activities of the US-LHC Accelerator Project, BNL is testing short samples of superconducting cables that will be used in the main LHC dipoles and quadrupoles. The purpose of these tests is to verify that the reels of superconducting cables as supplied by the vendors meet the required critical current specifications. The short-sample testing facility and the computer-assisted testing techniques for acquiring the data will be described. We also describe the data analysis, data storage, and data transmission methods

Thomas, R.

Ghosh, A.

Mcchesney, D.

Jain, A.

UNT Digital Library

BNL-71053-2003-CP Proceedings of the 1999 Particle Accelerator Conference, New York, 1999 TESTING AND EVALUATION OF SUPERCONDUCTING CABLES FOR THE LHC" R. Thomas', A. Ghosh, D. McChesney, and A. Jain, BNL, Upton, NY -. ,. ... Cable ~ Database I Absh-act Data Flow Events As one of the activities of the US-LHC Accelerator Project, BNL is testing short samples of superconducting cables that will be used in the main LHC dipoles and quadrupoles. The purpose of these tests is to verify that the reels of superconducting cables as supplied by the vendors meet the required critical current specifications. The short-sample testing facility and the computer-assisted testing techniques for acquiring the data will be described. We also describe the data analysis, data storage, and data transmission methods. 1 APPROACH Electrical tests of cable samples must be done during cable production so that cable manufacturing problems may be detected as early as possible. During the period that CERN is procuring superconductor cable for the LHC project, BNL is providing resources to verify the super- conducting properties of the cables. The BNL short-sample test facility is used to measure the critical current, I,,, of short (Sl meter) samples of LHC dipole and quadrupole cables. The number of tests that must be performed is set by the cable production schedule and reaches a peak rate of about 20 samples per week. The total number of tests that will be performed over the six-years of the collaborative effort will exceed 3000. A large quantity of information needs to be acquired, analyzed, and stored. Also, reports on individual runs, summary sample reports, and compatible raw data files must be regularly transferred to CERN. Because the data handling tasks themselves present the largest challenges, the database is the key organizing structure for all other operations. This approach is possible as a result of recent advances in networked databases and distributed object- oriented software programming. These allow software programs located anywhere on a network (either a local intranet or the world-wide Internet) to interact with a database using the client/server model. As samples are received, information about each sample is entered into a table (CableTrack) in the data- base. When an assembly of four samples is placed in a "Work supported by thc U. S. Department of Encrgy, Contract No. DE AC02-98CH10886. "Ernail: thornasl@bnl.gov sample holder for testing, information about the assembly is entered into the CableAssembly table. When the actual testing takes place, the data acquisi- tion program interacts directly with the same database to give the user a drop-down list of assemblies from which he selects the assembly being tested. From that selection alone, the data acquisition program can obtain information from the remote database regarding the physical character- istics of the samples being tested and their instrumentation wiring. Fig. 1 shows the data flow and database interac- tions. Figure 1. Selected tables of the Cable Database and interactions with the data flow events. When data are acquired, values are written into the CableWave table of the database describing the experi- mental conditions and, the name of the raw binary data file (a copy of which is automatically placed on the network file server). Once this information has been obtained, data analysis can be carried out on any machine connected to the network. (Software has been produced that loads data into workbooks, fits the data to a model, and writes results back into the CableAnalysis table of the database.) Other programs allow the user to select records from the Cable- Analysis table which the program then uses to produce summary reports. Proceedings of the 1999 Particle Accelerator Conference, New York, 1999 -50 Finally, result files, plain-text raw data files, sum- mary reports are shipped to CERN using ftp (file transfer protocol). Although there is a program to assist in this step, it has not yet been fully automated. Also, the con- struction of a web page that allows those at CERN to follow the status of any sample is still under development. 2.5 2 SHORT SAMPLE TEST FACILITY The standard tests are performed at 4.2 K. Approxi- mately 10% of the cable samples are being tested in superfluid helium at 1.9 K to determine the consistency of the AH shift of the IC, vs. H curve from 4.2 K to 1.9 K. Four samples can be tested in one cool-down of a single test station (cryostat), so two additional test stations are being built to meet the LHC production schedule. The layout of the four samples in the sample holder is shown in Fig. 2. The sample holder is placed in a cryostat which also holds a superconducting dipole magnet which can produce fields as high as -9 T at 1.9 K [I]. The magnet is energized by a 8.5 I& power supply; a superconducting switch allows it to operate in the persistent mode. As the critical current of the cable will generally be in the range of 10-20 kA, two 15 kA supplies are operated in parallel to supply the cable test cur- rent. Figure 2. Sample arrangement In addition to the power supplies and their controls and safety devices (quench detectors and fault detection circuits), the facility includes the instrumentation necessary for controlling the cryogenic environment and for measuring the critical current of the samples under test. Two computer systems are used: 1) a cryogenic system that monitors liquid helium levels, temperatures, and pressures and both sets and monitors the flow of helium through the gas-cooled leads, and 2) an experimen- tal system for controlling the sample power supply, taking data, and storing data in the SQL database. in the sample holder. 3 TEST The goal of the short-sample cable tests is to deter- mine the transport critical current of the samples. This critical current is a function of temperature and the magnetic field. In order to obtain standardized results for a specified reference temperature and reference field, raw data must be obtained for several applied fields with the samples at the temperature of the helium bath; that is, one acquires a set of critical currents, I,, at bath temperatures, T,, and applied fields, B,, for each sample. By pairing samples which are believed to have similar properties, it is possible to acquire data on two samples siinultaneously. Also, as there are three gas- cooled leads connecting the two sample pairs to the sample power supplies (see Fig. 21, four samples can be tested in a single cool-down, with the pairs being tested sequentially. To acquire the I, data, the operator first sets the current in the dipole magnet for the desired applied field, then connects the sample power supply to the first sample pair to be tested. He then enters the required information into the data acquisition program regarding the ramp rate and maximnuin current for the ramp on the form shown in Fig. 3. 1 Pleaee prawde the following lniormntlon 1 rPtCa#H seled the Cool Uown numbst'-, li LIS$! IliM tl!ie ,,,.XI 1 @ d o  . j$Y%l (No 30:ii;) 2- . ~ "  ! ............................................. . . . .  Please mlet Qt? -Which Ctyoatut arm you wing? r 1114 0 185 r TES PSPositive fh) Lead Connection .. j F B  r h  r c  ............................................................................ PSNsgariva (-1 Lsad Connec~ion " "- Voltuge Taps - Sample Loceuon 1 I v s c  r t ~ l * v r w  L c', l i i  P O  r v  r w  Vallag$ Taps-Sample Location 2 Figure 3. User forin for entering run information . Three high-resolution volt meters are triggered simultaneously as the current is ramped to obtain the voltage drops across the two samples and the current level as a function of time, as shown in Fig. 4. Cool Down 3879 Run 002 Is, Vsl,  VsZ vs. time I n 1  I I I 5 Proceedings of the 1999 Particle Accelerator Conference, New York, 1999 Several sets of data are obtained at different dipole field levels for each sample pair. 4 ANALYSTS AND REPORTING Once the raw data have been collected, analysis can begin on any workstation connected to the network, since all the required information for each run can be extracted from the database. On many occasions there is consider- able electrical noise visible on the signals, primarily as a result of phase and voltage flicker that is produced by the synchrotron accelerators located nearby. When this is the case, the use of a model and a fitting procedure allow the value of I, to be extracted. (See Fig. 5.) Cool Down 3888 Run 017 OlD9800lA-I AB vs vs. Is Is (kA) Figure 5. Noisy data and model fit. results. The results of the analyses are automatically stored in the database. The reporting application then extracts this information, converts the I, values to Ic;s (the critical current at the specified reference temperature, T,,,), and computes the peak field, H, experienced by the sample (the sum of the applied field and the self-field [2] ) .  Then the program performs a linear fit to the &(El) values to calculate I,, at the reference field. See Fig. 6. 18 17 16 15 14 ’ 13 12 11 10 5.5 6.0 65 7.0 7.5 H Cr-W Figure 6. Linear fit to experimental I, results. Other programs access the database to create plain- text files of results and reports and then transfer these to CERN. A web-based status page is under development which will always be current, since it uses Active Server Page technology to obtain information directly from the database whenever the page is accessed. 5 SUMMARY AND CONCLUSIONS Our experience to, date indicates that a database- centered approach to this data intensive cooperative program is both practical and feasible. The state of development of commercial operating system components for distributed applications, software development lan- guage tools, data analysis applications, and database servers is sufficiently mature that users can develop and maintain sophisticated clienthewer applications. Using the database as the organizing structure around which s o h a r e  is developed for carrying out the many tasks of the collaborative effort unifies all the elements of the process and makes it possible for the users to have a comprehensive understanding of the state of the project. The principal disadvantage is that this approach requires a rather complete understanding of what kinds of information are to be collected. If there has already been considerable experience with the procedures that need to be carried out and the difficulties that can possibly arise in acquiring and entering the data, then this approach is especially appropriate. If, on the other hand, there are many unknowns regarding what data it is necessary to collect and what difficulties may occur in collecting the data, a database-centered architecture may be less useful. As all the applications depend on the database tables, if it is necessary to frequently change the structures of these tables during the initial stages of the project to satisfy the requirements of one or another of the applications, these changes have a cascading effect and may require that other applications be updated. However, this is not a fault of the database-centered approach itself, but merely an indication of the inter- relatedness of the various tasks. In general this data-driven method is unsuited for new exploratory investigations of an open-ended nature, but is well suited for organizing repetitive experimental and reporting procedures of a known complexity. 6 ACKNOWLEDGMENTS The authors wish to thank A. Verweij and L. Obeli (CERN) for useful discussions. 7 REFERENCES [l] R. McClusky, K. E. Robins, and W. B. Sampson, “A Nb,Sn High Ficld Dipolc,” IEEE TI.ans. 011 Magnetics, Vol. 27, p. 1993 (1991). [2] M. Garber, et. af., “Thc Effect of Self-Field on the Critical Current Dctennination of Multifilamentary Supcrconductors,” IEEE Fans.on Magnetics, Vol. 25, p. 1940 (1989). 

TESTING AND EVALUATION OF SUPERCONDUCTING CABLES FOR THE LHC.

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Testing and evaluation of superconducting cables for the LHC

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