Injection problems: week 41

1. Injection problems: week 41 C. Bracco, W. Bartmann, B. Goddard, V. Kain, M.Meddahi, V. Mertens, J. Uythoven

2. Obstacle in MSI • Problem with 800 MHz in SPS • Other longitudinal problems leading to losses at injection

3. Started Fri 8th after 248b fill

4. Problem localised to MSIA-MSIB transition by beam losses B.Goddard et al.

5. Injection area investigations at the MSI • There is a clear problem with the RF fingers at the transition. Not clear how did it get worse suddenly. Need to find a different injection trajectory, for the time being while preparing an intervention for the technical stop or the Christmas stop Circulating beam Injected beam J-M. Dalin G. Arduini 13/10/2010

6. …Drawing picture of obstacle On Wednesday: Horizontal & Vertical Scan @ MSI monitoring losses at the MSIA, MSIB, MQ5, TCTH.4L2 and TCLIB, with pilot bunches High losses High losses old old • → move beam in septum • 4 mm Vertical • +1 mm Horizontal new new No losses No losses

7. → Mis-steer injection: match oscillation fromline with bump in the LHC Horizontal Bottleneck LHC 1 unit bump Vertical Bottleneck LHC

8. Orbit bump during injection.Removed before ramp Vertical: 1 unit Horizontal Injection oscillations afterwards after matching

9. TCDI Collimators set around new Trajectory 24 bunches

10. 8 Bunches Injection MSIB MSIA

11. 24 Bunches Injection MSIB MSIA

12. → Fill afterwards: > 1032 luminosity

13. MSI Bottleneck deteriorating • Could not inject high intensity anymore Saturday morning • After first 312b fill… • Adjustment of trajectory through MSI required (another 1 mm in both planes) + adjusting of bump in LHC; opened up TCLIb by 2 s • Injection oscillations were at 1.5 mm – need to be kept below 2 mm ! • MSI needs urgent repairing • In progress

14. Longitudinal losses 1) – RF in the LHC • Sensitive to capture losses in the LHC: • Debunched beam swept onto TDI during injection • Several mitigating measures in progress • LHCb BCM threshold now increased by factor 3 (ALICE has higher threshold so OK for now) • Investigating: relaxing sensitivity of critical BLMs (TCTVb) • Investigating: BLM sunglasses = blackout of BLMs during injection, possibly also for LHCb BCM • Investigating: injection cleaning with transverse damper a la abort gap cleaning. Machine protection issues have to be addressed • Investigating: shielding downstream of TDI/TCLIs – FLUKA simulations launched

15. Longitudinal losses – from the injectors 2a) • Thursday evening: losses on TCTVb a factor of 3 higher than normal from first injection onwards ~ 13 Gy/s • No abnormal transverse losses, capture in LHC looked perfect according to signals • Time structure from LHCb BCM: losses at ~ 700 ns and at ~ 100 ns before injection

16. Losses on rising edge of kicker waveform seen by LHCb At -700 ns, from uncaptured beam (beam in LHC)At -100 ns, from uncaptured beam or satellites (beam from SPS) Problem due to SPS 800 MHz not locking onto frequency…for many hours Missing diagnostics…SPS surveillance, and try to get signals from LHCb

17. Longitudinal losses – from the injectors (2b) • Saturday afternoon: one of the PS 80 MHz cavities was off during injection • losses on the TCTs (V and H) • Sunday night: losses again on the TCTs, lost several attempted fills, situation was unstable • No information in logbook

18. Conclusions • Physical limit in MSIA/B transition: being fixed • Need to reduce sensitivity to uncaptured beam from SPS and LHC: ongoing • Also need an improvement in diagnostics for beam quality coming from injectors… • Calibration measurements needed to quantify • Improved instrumentation and surveillance • SPS uncaptured beam before extraction – BQM? • SPS 800 MHz and PS RF states • Transverse losses from TCDIs least of worries at present…good steering and TCDI setup helps.

19. Other things • Abort gap keeper: allowed bucket numbers changed. • Last allowed bucket 31140