Expected field quality in LHC magnets E. Todesco AT-MAS With contributions of S. Fartoukh, M. Giovannozzi, A. Lombardi, F. Schmidt (beam dynamics) N. Catalan-Lasheras, P. Hagen, S. Sanfilippo, W. Venturini, C. Vollinger (data analysis) J. Beauquis, G. Bevillard, L. Deniau, E. Wildner (database) CERN, 20 th January 2005 XIV Chamonix meeting

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA2 MB: main dipoles 1104 in arcs, plus 128 in Dispersions Suppressors and in Interaction Regions MQ: main quadrupoles 360 in arcs, plus 32 in Dispersions Suppressors and in Interaction Regions MQM: quadrupoles In Dispersion Suppressors (48) and Matching Sections (38) MQY: large aperture quadrupoles In Matching Sections (24) MQX: final focus quads In Interaction Regions (32) Contents

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA3 Magnetic field of all magnets measured at room temperature All magnets tested at 1.9 K Only a fraction magnetically measured at 1.9 K The dashboard

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA4 3 steps to build the model of the field shape of the LHC Prototyping Gaussian distribution with average and sigma as expected During production Gaussian distribution with average and sigma as measured at 1.9 K or extrapolated from room temperature After slot assignment by Magnet Evaluation Board Each magnet has a fixed value. No more necessary to generate different machine The construction of the machine model

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA5 Best estimate of systematics at the end of the production Not allowed multipoles: within targets, a4 can be critical Allowed multipoles: we made two cross-section corrections b5 and b7 are marginal Main dipoles - expected systematics

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA6 b3: first order allowed harmonics - optimal situation 1.8 at high field (target [-3,3]) - OK -5.4 at injection (target [-10.5,10.5]) - OK b5: 1.2 at injection (target [-1.1, 1.1] given by dynamic aperture) This gives  reduction of dynamic aperture for 10-20% error in the correction of b5 [S. Fartoukh] This gives Q’’’ very slightly out of target, not a issue for nominal operation, only for MD requesting off-momentum measurement [S. F.] 0.0 at high field (target [-0.8, 0.8] at high field) - OK b7: 0.33 at injection (target [-0.3,0.1] given by dynamic aperture) This gives a reduction of dynamic aperture from 11.8 to 11.2  [S. F.] These values do not require a 3 rd action on the X-section Main dipoles - allowed systematics

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA7 Strong systematic component in Firm2 (0.5 units) corresponding to 0.1 mm (only) of systematic up-down asymmetry Partially compensated by negative systematic in Firm3 All data confirmed at 1.9 K Main dipoles - systematic a4

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA8 Un-elegant but effective solution: One Firm2 collared coil was assembled capsized in the cold mass a4 becomes negative, larger spread but zero systematic Solution available to steer average a4, if necessary Main dipoles - systematic a4, remedies

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA9 Rules of installations recommended by FQGW and used by MEB [S. Fartoukh] No mixing of inner cable (two types, 01B and 01E) Mixing of magnet manufacturers Allowed by no large differences between firms in integrated transfer function Main dipoles - random

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA10 Low spread of integrated transfer function between firms Main dipoles - random

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA11 Non-negligible spread of b3 due to different reasons Trends, X-section changes, non-nominal shims Main dipoles - random

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA12 Rules of installations recommended by FQWG and used by MEB For reducing spread of b3 Sector 7-8 cross-section 1 (35) and 2 [plus 2 to 4 cross-section 3] Sector 8-1 cross-section 2 (20) and 3 All others X-section 3 Up-down installation (local compensation) on the background Pairing of outliers Installing high b3 in one sector, and low b3 in another one Main dipoles - random

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA13 Sector 7-8 already allocated (only 5 missing) Sector 8-1 in progress (cable 01B, high b3) Tentative estimate on sector III (01B low b3) and sector IV (01E) Spread on integrated main field and b3 well under control The rest is within target, b5 marginal Main dipoles - random Estimate carried out on warm measurements adding in quadrature correlations to injection field

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA14 Best estimate of systematics at the end of the production Not allowed multipoles: within targets Allowed multipole: we made one cross-section correction Everything is OK Main quadrupoles - expected systematics

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA15 Spread in integrated field gradient is critical, 20% more than the limit of the budget for beta-beating (physical aperture) [A. Lombardi] Spread in b6 out of targets but probably not critical Main quadrupoles - expected random

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA16 Correlations not yet completely established [P. Hagen, S. Sanfilippo] Integrated field gradient, problems with calibration of measuring instruments at 1.9 K The spread is 5 units if only Single Stretched Wire measurements are selected Correlations of low-order multipoles (b3 a3 b4) not good Already between apertures and cold masses (both r.t.) is not good Also between cold masses (r.t) and 1.9 K is not good One magnet showed anomalous correlations This is due to a collar permeability higher than tolerance [F. Simon] High collar permeability strongly affects field gradient and multipoles at r.t. The effect disappears at 1.9 K Main quadrupoles - correlations

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA17 At room temperature, high permeability provokes low b6 Main quadrupoles - correlations

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA18 At 1.9 K the effect disappears, thus giving anomalous correlation For the first time, we are risking of not having complete information on the field quality machine Main quadrupoles - correlations

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA19 Features and critical points [N. Catalan, M. Giovannozzi] Individually powered spread b2 is not a problem if b2 is known, otherwise additional beta beating the knowledge of integrated b2 is necessary for the commissioning Similar problems to MQ [W. Venturini] 40% of MQY production affected by high permeability, thus leading to loss of knowledge of field quality based on only r.t. measurements Feature of MQM (and partially MQY) operated also at very low current, becomes difficult to optimize b6 at injection due to persistent current Impact of multipolar errors Some reduction of Dynamic Aperture is observed especially for MQY (large beta function !) at  (without linear imperfections) Quadrupoles in dispersion suppressors and matching sections: MQM and MQY

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA20 Quadrupoles in the IR region (final focus) 19 MQXA produced by KEK 16 MQXB produced by FNAL Results [R. Ostojic] MQXA in agreement with the expected, tight errors Except 1.2 units of systematic b4 (ovalization) MQXB in agreement with the expected, tight errors Impact on beam dynamics [F. Schmidt] At high field in collision, b4 can be corrected through correctors, not so critical But the correctors must be set at 100% 16 IR quadrupoles

Estimates of the LHC magnetic optics versus measurements January E. Todesco AT-MAS-MA21 Conclusions Knowledge of the machine Field quality of the machine