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Field Quality Challenges in HiLumi WP2 Meeting - A Summary of Design Options and Multipole Effects

This document summarizes the discussions from the HiLumi WP2 meeting held at CERN on June 11, 2013, focusing on field quality issues related to design options for large aperture magnets. Key considerations include coil width selection, operational field strengths, multipole effects, and the impact of saturation on performance. Several design challenges, such as fixed distances between beams and cross-talk, are explored, along with potential solutions for optimizing field quality in future accelerator magnets. The need for careful consideration of multipoles and operational parameters is emphasized.

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Field Quality Challenges in HiLumi WP2 Meeting - A Summary of Design Options and Multipole Effects

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  1. CERN, 11th June 2013 HiLumi, WP2 meeting FIELD QUALITY IN D2 E. Todesco CERN, Geneva, Switzerland This estimate relies on the workpresented by R. Gupta in Napa valleyHiLumi meeting https://indico.fnal.gov/conferenceDisplay.py?confId=6164

  2. DESIGN OPTIONS • Coilwidth: either 10 mm RHIC likecoil, or 15 mm LHC likecoil • One layer sinceweneedspace • Margin on loadline 20% minumum • So one has two options • LHC cable, 20% margin, 5 T operationalfield (7-m-long) • Smallercable or largermargin, 3.5 T operationalfield • as today, 10-m-long • Largerfield, worsefieldquality • Worse, but perhaps acceptable • First question: do weneed the additional 3 m ?

  3. DESIGN CHALLENGES • Large aperture, fixed distance betweenbeams, large cross-talk • Signs of evenmultipoles • B2 have opposite signs in the ap • B1 have the samesign • b2 have opposite sign

  4. ALLOWED MULTIPOLES • General framework : optimizationathighfield • Allowedmultipoles: strong saturation effect, to becompensatedwithgeometric • 140 units of b3, 20 units of b5 (5 T), reduced by a factor 2.5 at 3.5 T • I assume that the correction canbedonewith 20% error, soresidual 30 units and 4 units, probablyverypessimist

  5. ALLOWED MULTIPOLES • Random part • Allowedmultipoles: strong saturation effect, to becompensatedwithgeometric • 140 units of b3, 20 units of b5 (5 T), reduced by a factor 2.5 at 3.5 T • I assume a spread of 3-5% of the saturation effect, so • 5 units of b3, 1 unit of b5 • So spread of saturation dominates over spread of geometric (new situation) • Magneticshimmingcould help to reduce the spread of one multipole

  6. Quadrupole • General framework : the magnet has a very large quadrupole component due to two-in-one cross-talk • One could cure athighfieldwithasymmetriccoils, but I don’tthinkthisisneeded – reproducibleeffect • So I justgiveyou the numbers … 100 unitsat 5 T, 40 at 3.5 T • Also in this case a factor 2.5 gainedloweringfieldfrom 5 to 3.5 T • Random part – also in this case 5% of saturation, so 5 units

  7. OCtUPOLE • General framework : the magnetalso has a very large octupole component due to two-in-one cross-talk • This isbad and not soeasy to correct • The numbers: 40 unitsat 5 T, 15 at 3.5 T • Also in this case a faactor 2.5 gainedloweringfieldfrom 5 to 3.5 T • Random part – also in this case 5% of saturation, so2 units

  8. FIELD QUALITY GUESS

  9. FIELD QUALITY GUESS

  10. CONCLUSIONS • I provided the worst case of fieldquality • Weneed to know what to optimize • Is b2 a problem ? • Is b4 to bereduced ? – thiscanbedonewithironshaping • Hard to reduceboth b2 and b4 … • If the b3 and b5 are too large, weshould go to longer magnet • Real estimate of the possiblity of controlling saturation and itsspreadis not easy to judge • Goingfrom 5 T to 3.5 T (and from 7 m to 10 m) one gains a factor 2.4 in criticalmultipoles, bothsystematic and random

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