UPDATE ON THE MAGNETIC MODEL, PRECYCLES AND BETA-BEATING

1. FiDeL meeting, CERN 16th February 2010 UPDATE ON THE MAGNETIC MODEL,PRECYCLES AND BETA-BEATING P. Hagen, E. Todesco for the FiDeL team Magnets, Superconductors and Cryostats Group Technology Department, CERN

2. CONTENTS • Missing precycles in 2009 • The issue of the minimum precycle current • The issue of magnets with negative current nominal settings

3. WHAT WAS MISSING IN 2009 • The following magnets have not been precycled in 2009 • The block of 6 MQTL around IR3 and IR7 in Q6 • Spectrometer compensators (6 magnets) had no precycle • We had an issue in the bump correction of the spectrometers – it is not likely that this stems from the missing precycle, since they were operating at full current • Both families will be precycled in 2010

4. MINIMUM PRECYCLE CURRENT: foreword • In order to get on the ascending branch, the minimum current achieved during the precycle must be (much) smaller than the injection current Iinj>Iminpre We have collisions here, then we dump the beam We inject the beam here A correct precycle with Iinj>Iminpre

5. MINIMUM PRECYCLE CURRENT: FOREWORD • If on the other hand Iinj<Iminpre we can make very large errors since the model assumes we are on the ascending branch, whereas we are on the descending one • At low currents this error can be large (of the order of a few per mil) • During the ramp the error disappears since one recovers the right branch But the magnet has this field We inject the beam here A wrong precycle with Iinj<Iminpre

6. MINIMUM PRECYCLE CURRENT: MQWA • This wrong precycling happened for a few magnets • First case: MQWA – the precycle goes down to 35.1 A and we inject at 35.3/38.3 A • At 35 A the hysteresis gives a +4% error between the model and the actual magnet Measurements of MQWA hysteresis

7. MINIMUM PRECYCLE CURRENT: MQWA • This fits with what guessed by Rogelio on the ground of beta beating measurements

8. MINIMUM PRECYCLE CURRENT: MQXA • This wrong precycling happened for a few magnets • Second case: MQXA – the precycle goes down to 400 A and we inject at 408 A in IR1 and IR5 • But at 452 A in IR2 and IR8 – should be better • At 400 A the hysteresis gives a -0.4% error between the model and the actual magnet (30 units) in IR1 and IR5 Measurement of MQXA hysteresis

9. MINIMUM PRECYCLE CURRENT: MQXB • This wrong precycling happened for a few magnets • Third case: MQXB – the precycle goes down to 700 A and we inject at 708 A in IR1 and IR5 • But at 776 A in IR2 and IR8 – should be better • At 700 A the hysteresis gives a -0.6% error between the model and the actual magnet (60 units) in IR1 and IR5 Measurement of MQXB hysteresis

10. MINIMUM PRECYCLE CURRENT: MBW • This wrong precycling happened for a few magnets • Fourth case: MBW – the precycle goes down to 41.1 and we inject at 40.9A • Fifth case: MBRC – injection 80 A above in IP1 and IP5 Probably the effect is not strong (less than 10 units ?) – to be checked

11. CONTENTS • Missing precycles in 2009 • The issue of the minimum precycle current • The issue of magnets with negative current nominal settings

12. MAGNETS WITH NEGATIVE CURRENT NOMINAL SETTINGS • In 2009, the precycles for bipolar magnets have been implemented always as up-down to be on the ascending branch • Correctors will have either negative of positive current, according to the steering algorithm (orbit, tune, coupling) • Some magnets with dipolar power converter belong to the optics and have negative current settings: • 63 out of 128 MQTL in positions Q8 to Q13 • 4 out of 8 MQWB in positions Q4 and Q5 • These magnets have been on the wrong hysteresis branch in 2009 • Can this be a source of beta beating ?

13. MAGNETS WITH NEGATIVE CURRENT NOMINAL SETTINGS - MQTL • The MQTL have a very low residual magnetization • It is not modelled in FiDeL • Therefore this issue is not relevant, I would not take any action Measurement of MQTL hysteresis

14. MAGNETS WITH NEGATIVE CURRENT NOMINAL SETTINGS - MQWB • The MQWB have a non negligible residual magnetization • What is the effect of a wrong precycling ? • Should one correct it? Measurement of MQTL transfer function close to zero

15. Summary of BETA BEATING SOURCES IN THE FIELD MODEL IN 2009 • MQWA: magnets were on the wrong branch of the hysteresis due to a precycle minimum current larger than injection current (+4% error) • MQXA in IP1 and IP5: magnets were on the wrong branch of the hysteresis due to a precycle minimum current larger than injection current (-0.4% error) • MQXB in IP1 and IP5: magnets were on the wrong branch of the hysteresis due to a precycle minimum current larger than injection current (-0.6% error) • The block of 6 MQTL around IR3 and IR7 in Q6 has not been cycled – effect should be negligible • MQWB: half of them are on the wrong branch of the hysteresis since they have negative settings (error to be estimated - is it relevant?) • MQTL: half of them are on the wrong branch of the hysteresis since they have negative settings (should be negligible)

16. TUNE DRIFT DURING RAMP • Tune drift during ramp • The error in the transfer function of the MQWA (+4%), and in IR1 and IR5 MQXA (-0.4%) and MQXB (-0.6%) is present only at injection • Disappears during the ramp, where the right branch is recovered • What is the impact on the tune? • Is it related to the observed tune drift? • With these changes the machine could be considerably different from 2009 • Both in terms of tune trims and beta beating