MKI Erratic: Beam Related Aspects

1. MKI Erratic: Beam Related Aspects ABT/BTP-FPS-EC

2. Injection Scheme TDI Miss-kicked Injected batch MKI grazing CirculatingLHC beam grazing Injected batch - Kicked Circ. beam - Over-kicked inj. batch

3. TDI Grazing with Injected Beam • Nominal MKI kick = 0.85 mrad • TDI grazing: 86% kicker strength (14% missing), 6s beam envelope Beam 1 IP2 TDI MKI MQM D1 D2 MQX MQX Injected beam TCDD

4. TDI Grazing with Circulating Beam • TDI grazing: 14% kicker strength, 6s beam envelope Beam 1 IP2 TDI MKI MQM D1 D2 MQX MQX Circulating beam TCDD

5. MKI Waveform Rise time 0.9 ms  36-18 bunches (25-50 ns bunch spacing)  less critical Fall time 3ms  120-60 bunches (25-50 ns bunch spacing)  more critical Rise time: 0.9 ms Fall time: 3 ms Grazing Fall time injected Beam: ~ 90-45 bunches at TDI (~2 ms green) ~ 30-15 bunches escaping (~1 ms yellow)

6. MKI Waveform Rise time 0.9 ms  36-18 bunches (25-50 ns bunch spacing)  less critical Fall time 3ms  120-60 bunches (25-50 ns bunch spacing)  more critical Rise time: 0.9 ms Fall time: 3 ms Grazing Fall time circulating Beam: ~ 90-45 bunches at TDI (~2 ms yellow) ~ 30-15 bunches escaping (~1 ms green)

7. Number of Grazing Bunches Nominal MKI flattop of 7.86 ms: • Full injected batch: 144/288 (for 25/50 ns bunch spacing) kicked with 80-90% nominal MKI strength  Worst Injection scenario • Erratic event:144/ 288 (for 25/50 ns bunch spacing) circulating bunches kicked with 10-20% nominal MKI strength. Longer flattop  more bunches can graze the TDI!! Two erratic events with beam happened on July 28th

8. First Erratic: 28/7/2011 at 16:30:43 Normal (triggered) turn-on M. Barnes • Erratic (un-triggered) turn-on of MKI2 MS3 at full PFN voltage; • Interlocks detected erratic. Control (machine protection) philosophy is to trigger all MS and DS of system (within a delay of 1µs). Hence all 4 kicker magnets pulsed for up to 4.5µs. • Circulating beam was not in IP2 and therefore not disturbed. • Batch was extracted from SPS but saw no kick at MKI (already at zero current after the pulse) and went straight into the TDI. Erratic (untriggered) turn-on of MKI2 MS3

9. Loss Pattern Upstream of IP2 TDI Beam 1 Well known loss pattern during injection Downstream of IP2 Beam 1 Very clean, TDI stopping the injected beam, no magnet quenched! • In comparison to flashover event of April 18th in P8 (see next slides), cleaner in arc (no quenches) – TDI stopping the beam + (maybe) retraction of TCLIB in between

10. Flashover in P8 on April 18th • Injection of 2 × 36 bunches spaced by 2.2 ms Breakdown after ~2 ms All 36b of 2nd batch were kicked with 75-90% nominal MKI deflection • Beam was on LOWER TDI jaw • and over-kicked, i.e. breakdown • in second half of magnet • (LHCb signals support this) • Nearly all p+ of the 36b impacted • on the TDI/TCLIB (grazing)  12 magnets quenched Breakdown after ~2 ms (from kick waveform)

11. Loss Pattern Upstream of IP8 TDI Beam 2 Well known loss pattern during injection Downstream of IP8 Losses far in sector 7-8, 12 magnets quenched Beam 2

12. Second Erratic: 28/7/2011 at 18:03:09 Erratic (untriggered) turn-on of MKI2 MS3 M. Barnes • Erratic (un-triggered) turn-on of MKI2 MS3 occurred during resonant charging – sending current to one of the four kicker magnets; • Interlocks did NOT detect erratic of MS3 (at 33kV): hence no immediate action was taken to turn-on other thyratrons. PFNs discharged via the DS after 4ms (no further magnet current). Interlocking problem to address. • The failure occurred early in the charging process, and the extraction from the SPS was inhibited; • The circulating beam which was swept over the aperture and protection elements (~17% of normal kick) for ~8-9µs  150-190 bunches

13. Loss Pattern Upstream of IP2 TDI Beam 1 Losses starting at TDI, no injection loss signature  only circulating beam kicked by MKI Downstream of IP2 Beam 1 Losses far in sector 2-3, 3 magnets quenched

14. Beam lost: Not Dumped Some beam missing • Intensity before dump: 517 bunches - 5.81e13 p+ (from XPOC) • Intensity dumped: 344 bunches - 3.64e13 p+(from XPOC) • Beam lost: 173 bunches - 2.15e13 p+ (~186 bunches of 1.15e11 p+)in agreement with 150-190 bunches expected • For operation with 25 ns bunch spacing  300-380 bunches

15. How Many Protons at TDI? Radiation monitors and BLM used to estimate the number of protons at the TDI and (possibly) downstream elements (difficult for MQX since no calibration factor is available. 1.29 First Erratic: Nb1 =144 bunches at the TDI (upper jaw) Second Erratic: Nb2 =?? bunches at the TDI (lower jaw) Simple ratio: Nb2 = Nb1 / 1.29 = 112 b 65% of the “lost” bunches In agreement with BLM measurements (A. Nordt)

16. BLM analysis (A. Nordt) • Number of protons lost at each element from Q6.L8 (Q6.R2 for B2) up to Q16.L8 (Q16.R2 for B2) • Combined results for: • Q6 quench margin at injection MD • Two erratic MKI events for B1 • Flashover event for B2 • Highest loss level recorded is indicated (blue: no quench, red: quench) MB MB MB MB MB MB MB MB MB MB

17. BLM analysis (A. Nordt) Beam No calibration factor available for triplet magnets (not possible to transform Gy/s in number of protons) Triplet magnets quench for losses higher than 21 Gy/s (BLM not in saturation) Q3 Q2 Q1 Q1 Q2 Q3

18. ALICE (from M.Lechman’s talk MPP) • The values of the threshold for the beam background were exceeded: • 16:30 - 80 times • 18:03 - 3559 times • 9 out of 17 sub-detectors were affected during the second erratic event • All subsystems but Silicon Drift Detector (SDD) recovered using standard procedures • SDD calibration system - investigation ongoing • We are close to limits of safety With actual MKI logic  up to a factor of 2 higher intensity (25 ns bunch spacing) expected in case of MKI erratic!

19. Related issues (from Rudiger) • Detecting erratic firing and trigger other kickers did not work. Are we sure that it would work for the beam dump kickers? • Completely different logic: • MKI only retrigger when a fault detected • MKD-MKB retrigger sent out at every dump and checked by IPOC • TDI aperture: • Nominal aperture: 6.8 s = 4.8 mm for e =3.5 mm • Actual e = 1.5 mm  4.8 mm = 10.4 s Should TDI be closed to, for example, 3.9 mm = 8.5 s ?? Impedance, aperture, heating effects to be checked!

20. Summary • Injection protection has worked (again) to prevent serious damage: • TDI intercepting miss-kicked beam (65%-100%) • High losses on downstream elements in case of grazing  magnets quench • ALICE: • recorded losses up to a factor ~4000 above thresholds • SDD did not recover using standard procedure • Very close to safety limit BUT up to a factor of 2 higher losses might occur, in case of missing retrigger, if MKI Voltage threshold logic unchanged • To be understood in more detail why the retriggering did not work • MKI new logic: remove voltage threshold  retriggering always possible also for low voltage (next TS), to be tested • Switch changed  no more erratic events observed • First estimates of quench limit: • MB: 2e9 p+ • MQ: 5e9-4e10 p+ • MQX: < 21 Gy/s (missing calibration factor)