1. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 1 Field Quality Updates HQ/QXF and D2 GianLuca Sabbi Acknowledgement: Joe DiMarco, E. Todesco, X.Wang, and the entire LARP/HiLumi collaboration High Luminosity LHC Annual Meeting Daresbury, UK, November 11-14, 2013

2. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 2 Outline IR Quadrupoles:  Plans for assessment and optimization of triplet field quality From HQ to QXF models and prototypes  Estimating the QXF field quality at high field Fabrication tolerances based on HQ experience Correction with magnetic shims  Analysis and control of eddy current effects using cored cables  Analysis/control of persistent current effect with magnetic shims D2 dipole: Design strategy using asymmetric coils Comparison with current tables and outlook

3. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 3 IR Quad field quality assessment HQ models are currently the main experimental platform for field quality: HQ01: first to incorporate alignment at all stages of coil fabrication HQ02: first to incorporate cored cable for control of eddy current effects HQ03: first set of coils fabricated with uniform design/process Approach: develop/check models using HQ data, then apply to QXF Start to transition to direct QXF measurement/analysis in mid-2015

4. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 4 Triplet Error Tables Focus on: uncertainty & random components (high field, lower order) eddy current (not in table) & persistent current effects E. Todesco

5. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 5 Estimating collision field quality Current tables calculate random errors assuming block positioning errors of 30  m (standard deviation) for not allowed harmonics, and four times larger values for b 6, b 10 and b 14 These assumptions were derived from analysis of HQ01, but rely on a series of measurements taken along the straight section of a single short magnet – very problematic, low confidence level HQ02 is one additional step to understand fabrication tolerances and the possibility to perform corrections based on warm measurements HQ03 will provide a more direct assessment based on a uniform set of coils and processes QXF models are will provide more direct information, once a stable coil fabrication process is established AP feedback is that further reduction of the errors is desired (WP2 report M24-27)

6. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 6 Random error estimates in HQ01 Simulation of random errors due to coil fabrication tolerances fits HQ01 measured harmonics (n=3 to 7) for a block positioning error of 30 µm Flat dependance for n>7 attributed to limited probe sensitivity Improved in later tests using multi-layer PCB probes by Fermilab Probe radius still limited by anti-cryostat, need to increase X. Wang

7. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 7 HQ harmonics (normal, high field) X. Wang,J. DiMarco

8. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 8 X. Wang, J. DiMarco HQ harmonics (skew, high field)

9. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 9 Axial scan of b3/a3 in HQ02a Low order harmonics (n=3, 4) show a clear longitudinal pattern Prevents from estimating random errors based on axial measurement Confirmed using a short probe to exclude smoothing effect Resulting errors appear to be outside the 30  m envelope Analysis focusing on geometric errors with long axial wavelength J. DiMarco

10. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 10 Correlating to geometric errors Ramp Pole block displ. Field errors are generally consistent with observed geometry deviations We need to implement more rigorous conventions on test setup to correlate measured field errors with specific locations in the magnet X. Wang

11. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 11 Magnetic shims for collision FQ Several past studies including test/application in magnets (RHIC, MQXB) Typically relying on 8 independent shims at quad-symmetric locations Design goal: sufficient correction strength at high field, minimal saturation Application to higher field magnets has challenges and opportunities Two options have been analyzed for possible application in HQ Location 1 (MQXB) Location 2 (baseline)

12. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 12 Effect of one shim in location 2 X. Wang Reasonable strength for n-3,4 at the level of the error table A first implementation is planned in HQ02b

13. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 13 Eddy current harmonics in HQ Large dynamic effects observed in LARP quadrupoles (TQ/LQ, HQ01) A thin (25  m) stainless steel core with partial coverage (8mm, 60%) and biased toward the thick edge was included in HQ02 cables Increased the effective R c from 0.1-0.4 μΩ (HQ01) to 2-4 μΩ (HQ02) with a corresponding decrease of the observed errors ParameterUnitHQ01eHQ02a Core material--SS316L Strand diametermm0.800.778 Cable widthmm15.1514.77 Cable mid thicknessmm1.4371.376 J. DiMarco, X. Wang D. Dietderich

14. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 14 Eddy current estimates for QXF X. Wang Systematic (R c = 1 μΩ, scales with 1/R c ) Random Eddy current effects contribute to both systematic and random components Assumed cable parameters: w = 18.638 mm, L pitch = 109 mm, N s = 40 Ramp rate, 14.6 A/s, R ref = 50 mm

15. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 15 Core design optimization X. Wang Core width and position in cable and coil can be used to achieve full compensation of eddy current harmonics with lower R c for stability and protection

16. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 16 Angular dependence of the shim contribution to the harmonics at 1250 A (negative peak) Thin iron strips placed in the bore at selected angular locations can effectively compensate for persistent current effects Magnetic shims for injection FQ X. Wang

17. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 17 Example of application to HQ  Negative peak reduces from -30 units to -3 units  Could be optimized differently, need to discuss with AP  Plan to include in HQ03 (some practical issues in HQ02b) X. Wang

18. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 18 Flux-jump effects  Spikes in harmonics have been observed during ramps  Correlated/triggered (but not directly caused) by flux jumps  Large effect at 4.5K, but significantly less at 1.9K  Suppression of eddy currents by core also helps  Additional studies required to understand mechanism HQ01e (no core) at 4.5KHQ02a (w/core) at 4.5K & 1.9K X. Wang

19. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 19 D2 Error Tables (low order, normal) Current version (1.4, October 2013): Previous version (1.3, July 2013):

20. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 20 Magnetic design strategies 1.Correct both geometric and saturation through iron yoke design Coil is optimized for single aperture (left-right symmetric) Traditional approach, but difficult for HL-LHC parameters 2.Design iron yoke for small saturation and correct the geometric component using at the coil level (requires asymmetric coil) A demonstration case was developed using simple yoke design Compares favorably with v1.4, further improvements possible Next steps: Latest results from both magnetic design and simulations will be presented at this meetings Using this feedback, discuss priorities/tradeoffs and establish optimal magnet design targets for best machine performance Develop fully optimized design to meet targets

21. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 21 Feedback from magnetic design Simple window-frame inner yoke profile provides saturation within v1.4 targets Currently using LHC cable for added margin over RHIC (55% SSL at operating point) Improvements in the yoke design are clearly possible to decrease saturation and fringe field, and increase contribution to main field No absolute constraints on aperture, operating field, field quality – trade-offs are possible We demonstrated (to our satisfaction) that this design approach has the needed flexibility, but it is not efficient to further optimize before reviewing key targets/priorities Full optimization should start from iron yoke, then coil

22. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 22 Comparison with v1.4 (low order) Still to be analyzed, expect similar Persistent current effect not analyzed – values from table were used for odd terms, should be recalculated for actual coil design and even components will appear (*) Still to be analyzed, expect similar

23. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 23 Comparison with v1.4 (high order) Error tables assumptions: high order systematic can be fully controlled at the design level, small/no saturation, uncertainty/random from previous fabrication experience Preliminary design was optimized within a few units and we can expect that after full optimization high orders will be dominated by uncertainty/random components Still to be analyzed, expect similar Still to be analyzed, expect similar

24. HL-LHC Meeting, November 2013Field Quality Update – G. Sabbi 24 Summary Ensuring high field quality in QXF requires full understanding and control of a broad range of issues Systematic errors  magnet, tooling and part design Random errors  fabrication tolerances (coil and structure) Eddy current effects  cable parameters and tolerances Magnetization effects  conductor parameters & tolerances For schedule reasons, HQ is the main experimental platform to support the machine design HQ03 with uniform set of coils will be particularly critical Correction capabilities based on warm magnetic measurements are essential to achieve stringent field quality requirements with new technology, few prototypes, and small series production Conceptual design of D2 provides a basis to update the performance parameters and error tables including feedback from AP simulations