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REPORT ON INVESTIGATION OF POSSIBLE MAGNET RELATED ISSUES IN THE TEVATRON

REPORT ON INVESTIGATION OF POSSIBLE MAGNET RELATED ISSUES IN THE TEVATRON.

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REPORT ON INVESTIGATION OF POSSIBLE MAGNET RELATED ISSUES IN THE TEVATRON

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  1. REPORT ON INVESTIGATION OF POSSIBLE MAGNET RELATED ISSUES IN THE TEVATRON G. Annala, P. Bauer, R. Cargagno, J. DiMarco, N. Gelfand, H. Glass, R. Hanft, D. Harding, R. Kephart, M. Lamm, A. Makulski, M. Martens, T. Peterson, P. Schlabach, D. Still, C. Sylvester, M. Tartaglia, J. Tompkins, G. Velev, M. Xiao Also many thanks to L. Bottura (CERN), H.D. Brueck and B. Holzer (DESY), G.L. Sabbi (LBNL), A. Tollestrup and V. Shiltsev for their ideas, opinions, suggestions and help! Pierre Bauer

  2. INTRODUCTION D. Finley et al. 1987 • Tevatron Dipole Magnets – an Overview • Measurement of Dynamic Effects in Tevatron Dipoles • Discussion of Possible Magnet Issues in the Tevatron Pierre Bauer

  3. I TEVATRON DIPOLE MAGNETS • Dipole Models • Production Magnetic Measurement Data • Field Profiles Pierre Bauer

  4. THE TEVATRON DIPOLE MODELS - BODY x) Data are from production measurements (more details later). xx)Tevatron dipoles have strongly differing b2 in body and ends, that, on average compensate when integrated over the magnet length! Pierre Bauer * magnetic multipoles quoted at 1 inch (=2/3 of bore radius)

  5. THE TEVATRON DIPOLE MODELS - END x) Data derived from production measurements (more details later). Pierre Bauer * magnetic multipoles quoted at 1 inch (=2/3 of bore radius)

  6. FIELD PROFILE IN END Results of the calculations presented here are not for the “average” end. Pierre Bauer

  7. MAGNETIC MEASUREMENT ARCHIVE DATA* J. Tompkins / R. Hanft Pierre Bauer * magnetic multipoles quoted at 1 inch (=2/3 of bore radius)

  8. Calculated from “Up-down-average” of archived production magnetic measurements for approx. all magnets installed. Down-stream position Up-stream position Body position J. Tompkins / R. Hanft * magnetic multipoles quoted at 1 inch (=2/3 of bore radius) THE TEVATRON DIPOLE NORMAL MULTIPOLES* Pierre Bauer

  9. Calculated from “Up-down-average” of archived production magnetic measurements for approx. all magnets installed. Down-stream position Up-stream position Body position J. Tompkins / R. Hanft * magnetic multipoles quoted at 1 inch (=2/3 of bore radius) THE TEVATRON DIPOLE SKEW MULTIPOLES* Pierre Bauer

  10. helix AVERAGE FIELD PROFILES IN DIPOLECALCUL-ATED FROM TABUL-ATED (Geometric) MULTI-POLES Pierre Bauer J. Tompkins 2002

  11. II DYNAMIC EFFECTS IN TEVATRON DIPOLES • Introduction to Dynamic Effects • Historical Review of Tevatron Magnet Measurements • Some Recent Results Pierre Bauer

  12. current flat top injection porch pre-cycle: MP drift at constant coil current & SB to the hysteresis loop at the ramp- start. reset time 1-2u Drift & SB in all ”hysteretic” multipoles -powering history dependent. ~15 A / 15 mT/ 7 GeV DYNAMIC EFFECTS -BASICS back porch Pierre Bauer P. Schlabach

  13. +DB -DB DYNAMIC EFFECTS IN TEVATRON DIPOLES – QUALITATIVE MODEL Current distribution is not uniform in the cables and changes as a function of time, generating a time-variable, alternating field along the Strands. Pierre Bauer L. Bottura/CERN 2002

  14. DYNAMIC EFFECTS IN TEVATRON DIPOLES – PREVIOUS STUDIES Pierre Bauer

  15. MAGNETIC MEASUREMENTS AT MTF MTF today has 7 test-stands to perform magnetic measurement of Fermilab magnets, superconducting IR quads for LHC, high field (Nb3Sn) magnets. Pierre Bauer

  16. 87 - DISCOVERY Pierre Bauer D. Finley et al. 1987

  17. Magnet Meas. – RL 1001 88 - MEASUREMENTS Pierre Bauer R. Hanft et al. 1988

  18. 92-MEASUREMENTS Pierre Bauer D. Herrup et al. 1992

  19. 96-MEASUREMENTS Pierre Bauer J. Annala et al. 1996

  20. MAGNETIC MEASUREMENTS – 02/03 J. Tompkins / G. Velev / R. Hanft Pierre Bauer

  21. III Discussion of Possible Magnet Issues in the Tevatron • Temperature Variations • Tune and Coupling Drift • Main Field Drift • Analysis of the b2-Compensation in the Tevatron Pierre Bauer

  22. QUANTITATIVE ESTIMATE OF DRIFTING SKEW AND NORMAL QUADS b1 drift needed in dipole to explain tune drift: a1 drift needed in dipole to explain coupling drift: Db1/ Da1 = ~0.1 u in dipoleto explain tune/coupling drift Pierre Bauer

  23. 0.2mm 0.1mm 0.1mm 0.05mm 0.2mm 0.015° 0.03° 0.012° 0.006° possible sources of 1u of a1 (up-down asym) & b1(left-right asym): DRIFTING a1 AND b1 IN DIPOLES? “smart-bolting” should have taken care of most of these! coil roll (“cryostat- instability”) – has been addressed! However, all the above explains GEOMETRIC a1/b1! The only mechanism that we found to explain HYSTERETIC a1 is: up-down difference in superconductor properties (e.g. Jc)! b1 drift maybe main field decay in quads? Pierre Bauer

  24. DRIFTING a1 AND b1 IN DIPOLES? Feed-down from b2 due to misalignment of dips & T:SD is most likely cause (see M. Martens talk) of most of the tune and coupling drifts; Is there drifting a1, b1 in the magnets? Production goal: zero geometric a1 and b1. This, however, does not exclude hysteretic b2: TC0269 clearly shows a hysteretic and a drifting skew quadrupole: Pierre Bauer R. Hanft / G. Velev

  25. ~0.5 units of main field drift in quads could explain Tev tune drift. Measuring main field decay with rotating coils is difficult, NMR is preferred technology. HERA and LHC observe dipole field drift at const excitation (note: issues related to longitudinal field variations); DRIFTING MAIN FIELD? also: low-beta quad effects were checked (running tune drift experiments with low-beta off) – see M. Martens et al. Pierre Bauer L. Bottura et al / CERN

  26. b2 DRIFT & SB FIT USED IN TEVATRON current b2 drift&SB correction was derived from magnetic measurement campaign of 96: drift: snapback: Pierre Bauer J. Annala

  27. b2 DRIFT & SB FIT: CURRENT VS 96 There were, however, small modifications made to improve machine performance: Pierre Bauer

  28. The (relative) agreement with magnet TC 1052 is very good at t>1 min, especially for flat-top times>10 min (standard flat-top in Tev pre-cycle is 20 min). COMPARISON b2 FIT VS MAGNET MEASUREMENT Pierre Bauer

  29. TC0269 D tSB b2 DRIFT&SB in RECENT MEASUREMENTS Drift amplitude at injection (after a 30 min injection porch) and SB time after a standard pre-cycle (20 min flat-top, 1 min back-porch) as recently measured in different magnets and as calculated with Tevatron b2 compensation fit. Pierre Bauer G. Velev

  30. DRIFT STARTING VALUE VARIATION b2 at start of drift is ~-1 unit to allow matching of fit with data at times t>1min + additional history dependent contribution of ~0.1-0.2 u). Hysteretic loop is believed to be invariable, that is un-affected by powering history and (within the range of interest) more or less independent of ramp-rate. Artifact of longitudinal field variations? Pierre Bauer G. Velev

  31. Exploring different fit algorithms for snap back: Exponential vs. polynomial fit of snap-back. Advantages of the exponential fit: • Less sensitive to variations in snap-back time • More in tune with physics (see 2 strand models) • Better fit? EXPLORING DIFFERENT SB FITS Pierre Bauer G. Velev

  32. EFFECT OF DRIFT DURATION Physics argument: the further the drift the longer the snapback time. Beam and magnet measurements show a ~constant snapback time independent of the porch duration  parabolic ramp!! Varying the injection porch time between 30 and 120 min TC0269 Drift compensation algorithm was formulated on the basis of 15 min measurements. Pierre Bauer G. Velev

  33. There, the reconstructed b2 loop is compared to recent beam-based b2 measurements and recent magnet measurements. BEAM & MAGNET b2 STUDIES COMBINED The magnet measurements are clearly “off” the average. This, however, is consistent with the production variations of the “width” of the loop (see error bars). Issue: single magnet vs. average of all magnets! Pierre Bauer M. Martens / M. Xiao

  34. CONCLUSIONS AND OUTLOOK • No show-stopper found! • Not conclusive regarding main field and a1/b1 drifts • b2 compensation OK except for minor details • Increase measurement sample - more drifts and snapbacks • More data on possible a1, b1 drifts in Tev dipoles • Collaboration with Cern – improvement of understanding of dynamic effects in magnets • Test a quadrupole for main field drift • Elimination of pre-cycle? • Continue to support Tevatron operation Expect further report from G. Velev on magnetic measurements soon.. Pierre Bauer

  35. MISCELLANEOUS SLIDES Pierre Bauer

  36. TEV DIPOLE – TEMPERATURE PROFILE • Issues: • stratification of two-phase • poor heat exchange betw. in/out single-phase flow •  ~ 100 mKDT across coil bottom/top 22 g/sec Linear heat load: ~10 W/dipole  ~25 mK / longitudinal magnet DT Pierre Bauer T. Peterson et al. 1997

  37. THE TEVATRON DIPOLE – CRYO-SYSTEM Heat load: 10 W/dipole  250 mKDT along magnet string), “day-to-day” temperature variations less than 50 mK. Average temperature ~ 3.9 K J. Theilacker/A. Klebaner Pierre Bauer

  38. Note: The end multipole distribution presented here is not that of the average Tevatron dipole as defined from the production magnetic measurements. It is, however, within ~1s of the average, and therefore a realistic end. b6, b8 & b10 PROFILES IN END* Pierre Bauer * magnetic multipoles quoted at 1 inch (=2/3 of bore radius)

  39. helix AVERAGE FIELD PROFILES IN DIPOLE BODYCALCUL-ATED FROM TABUL-ATED MULTI-POLES Pierre Bauer J. Tompkins 2002

  40. helix AVERAGE FIELD PROFILES IN DIPOLE ENDCALCUL-ATED FROM TABUL-ATED MULTI-POLES Pierre Bauer J. Tompkins 2002

  41. TEV b2 ANALYSIS SUMMARY Besides some minor issues regarding the details of the b2 compensation we found no “smoking gun”. We can use our knowledge of the magnet properties to reconstruct approximately the “average” hysteresis loop. The loop shown here was reconstructed from the archive data and recent magnet measurements. Pierre Bauer

  42. MAGNETIC FIELDS - NOMENCLATURE The following conventions are used here for the multipole expansion of the magnetic field: Complex formulation of cross-sectional fields  By+iBx is analytical outside conductor  expansion in a Taylor series  multipole coefficients e.g. – if only b20, that is a pure sextupole field: Pierre Bauer

  43. F D T:QF Horz BPM T:QD Vert BPM T:SF T:SD Tevatron Dipole Tevatron Quad corrector (There are 772 Tevatron dipoles) Tevatron Sextupole corrector Tevatron Quadrupole Tevatron Beam Position Monitor F TEVATRON STRING Pierre Bauer Courtesy - M. Martens

  44. MAGNETIC MEASUREMENTS - 2 Pierre Bauer

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