Magnetic requirements for the commissioning

1. CERN, 10th February 2006 Chamonix summing up Magnetic requirements for the commissioning E. Todesco Accelerator Technology Department Magnet and Superconductors Group Acknowledgements: the speakers, S. Ramberger, J. P. Koutchouk

2. Introduction • 85% of the main dipole coils and 100% of the main quadrupole coils have been wound and assembled • What has been done is done … • Activities related to magnet performances and field quality are shifting • from the follow-up of the production, and corrective actions • to gather all the knowledge that could be useful for the commissioning Main quadrupoles Main dipoles E. Todesco AT-MAS-MA

3. Structure of the session • Behavior of magnets for operation • Orbit, tune and chromatic correctors (R. Steinhagen, W. Venturini) • Dynamic effects for the field model (M. Lamont) • Estimating quantities relevant for commissioning • Beta-beating (S. Sanfilippo) • Quench level without beam (P. Pugnat) • Other • MEB activities (L. Bottura) • Parasitic fields estimates (A. Devred) E. Todesco AT-MAS-MA

4. Hysteresis in orbit correctors (R. Steinhagen) • With a pre-cycle 0A – 55A – 0 A • The remenant field corresponds to a kick of 0.560.05rad • Both systematic and random effects are within tolerances  No need of a degaussing cycle to set the systematic to zero • Feedback correction • Small loops are giving an hysteresis which does not affect the feedback algorithm Measurements at Block4 by W. Venturini et al. E. Todesco AT-MAS-MA

5. Hysteresis in tune and chromatic correctors (W. Venturini) • Tune correctors (MQT) • It would be better to operate them at small, non-zero current (1.5% of max corresponds to 0.2 of detuning) • Global hysteresis gives a detuning of 0.005 • Decay of b2 gives 0.01 of detuning • A correction with a linear model gives an uncorrected detuning of 0.0015 • Hysteresis can be ignored • Chromatic correctors • Small loops are giving an hysteresis which does not affect the feedback algorithm E. Todesco AT-MAS-MA

6. Field model deliverables (M. Lamont et al) • Field model (FiDeL) • Magnetic measurements  fitting procedure and extraction of model parameters(by N. Sammut, L. Bottura, J. Micallef) • Slot allocation  evaluation of the behavior of magnets connected to the same power supply • Deliverables • Sector test • Transfer function of MB, MQ, correctors • Decay prediction • Cycling prescription • Commissioning • Everything for sector test plus snapback Example of snapback fit E. Todesco AT-MAS-MA

7. Estimates of beta-beating (S. Sanfilippo et al) • Beta-beating: • Error in the optic functions due to imperfections (mainly on the quadrupole strength) • It reduces the mechanical aperture for the beam • The budget is 21% of maximum beta-beating • Previous experience • Beta-beating in LEP was 200% at the beginning of commissioning • LTC asked for estimates: are imperfections under control ? • Previous work • Different sources of beta-beating have been identified • Targets/estimates based on the early production have been given E. Todesco AT-MAS-MA

8. Estimates of beta-beating (S. Sanfilippo et al) • New estimate: • Based on measured values, slot allocation, estimated precision of measurement systems (by P. Hagen, J. P. Koutchouk, M. Giovannozzi, T. Risselada) • Effect of cell MQ, of MB, and of individually powered MQ taken into account • Feed down due to misalignment still relies on estimates – measurements will be included soon • Results within target E. Todesco AT-MAS-MA

9. Expected quench level without beam (P. Pugnat) • Available data • 908 main dipoles tested, 115 with a 2nd thermal cycle • 196 main quadrupoles, 9 with a 2nd thermal cycle • Statistical analysis to guess how many quenches are needed to work at 7 TeV • 25-306 quenches per octant in the dipoles (depending on detraining), with a two sigma error • 86 quenches per octant in the quadrupoles, with a two sigma error E. Todesco AT-MAS-MA

10. What we gained with sorting (L. Bottura) • Magnet Evaluation Board activity is at full speed • 1/2 of the dipoles and 1/3 of the quadrupoles allocated • Mixing of dipole manufacturers in sectors • Small systematic differences in field quality between firms • The same inner cable in the same sector (when possible) • Criteria (S. Fartoukh et al.) • Geometry • maximizing mechanical aperture • Field quality • Minimizing σ(b1) in dipoles (avoid eating the orbit correctors budget) • Minimizing σ(b2) in quadrupoles (beta-beating, mechanical aperture) • Minimizing σ(b3) in dipoles (3rd order resonance, dynamic aperture) E. Todesco AT-MAS-MA

11. What we gained with sorting (L. Bottura) • Geometry • Dipole allocation taking into account the actual beam dimension (worse magnets in mid half-cell positions) • Quadrupole installation with tilts and rolls in a few cases to maximize mechanical aperture What we would get with nominal installation • Field quality • b1 sorting used for the early phase of production (first sector) • In the first sector, random b3 was 15% larger than target sorting allowed to stay within targets (improvement by a factor 3 !) • Sorting still used to further improve random b3 (you never know …) installation with tilt and roll E. Todesco AT-MAS-MA

12. Chasing parasitic fields (A. Devred) • Beam screen • New analysis of the measurements at block4(W. Venturini)showagreement with simulations(B. Auchmann) • Smaller effect on b5, b7 can be due to misalignment • Connection cryostat • PbSb plates in the connection cryostat can become superconductive and quench • Kick on the beam well above specification • Solution: add a thermal link to keep “warm” the PbSb (above Tc) (A. Poncet et al.) • Effect of bus-bars • 3d models have been built, (B. Auchmann) field and impact on the beam is being evaluated (C. Vollinger, J. P. Koutchouk) E. Todesco AT-MAS-MA

13. Future outlook • Optimize the magnetic measurements activities to get as much information as possible (Production follow-up is less critical now) • Dynamic components of main quadrupoles • Transfer function of special quadrupoles • Statistics on the dynamic components of dipoles • Characterization of all correctors (cycles, feedback) • Translate the magnetic and geometric measurements into a model of the machine • Including the slot allocation • Start estimating the relevant quantities for the beam • TF for MB and MQ, detuning, natural chromaticity, (resonances) • Different TF and corrector settings for octants • Be ready for the first benchmark with the beam E. Todesco AT-MAS-MA