LHC Injection Sequencing MD 16/23/2009 Injection sequencing / BCM R, Giachino, B. Goddard, (D. Jacquet), V. Kain, M. Meddahi, J. Wenninger

Aims 2  Execute complete/nominal LHC injection sequences to ring1/2 under LHC mastership. Beam send to the TT40/TT60 TEDs. Also : investigate delays in the timing system  All aspects of this test had already been ~fully tested separately before, with the exception of the requests for N (0-4) batch injections into the SPS. 6/23/2009 Injection sequencing / BCM

Beam phases 3 Injection sequencing / BCM 6/23/2009 The test was performed in 2 phases:  Phase 1, injections of 12 bunches of ~1E10 p/b. Extraction setup with 1 injection. Extraction kicker delay tuning with 1-4 injections.  Phase 2, injections of 72 bunches of ~2.5E10 p/b. Execution of nominal injection sequences. MKE4MKE6 Shifted by ~2  s to avoid largest waveform excursions (JU proposal) Observed a systematic time offset of ~2  s between the beam & MKE traces. ???? 2  s/div

Observations : sequencing 4  Nominal filling was never fully executed, due to a mistake in the timing sequence programming:  The first injection (of N) was never send to the SPS if it followed a cycle without beam. This means that even in the best of all cases, the first injection into the LHC was never executed properly (since one always starts without beam !).  Execution delay.  When the injection sequencer was waiting for the Injection Quality Check (IQC, close to the end of the SPS cycle), it was always missing one full SPS cycle due to delays in the timing system.  We wanted to study the delay by adding ‘zero’ cycles at the end of the timing sequence, but then we lost the LHC mastership. >> Both issues have been identified and fixed (to be tested) by J.C. Bau. 6/23/2009 Injection sequencing / BCM

Nominal LHC filling cycle (p) 5 Injection sequencing / BCM 6/23/2009 Minimal length cycle : 21.6 s First 625 ms Flat top ms Extraction ~19500 ms  Delay between extraction and start of the next cycle is only ~2 seconds –too short to perform a decision in time for the next cycle : need to understand minimum extra length to be added… Remember that the booster injects beam ~ 3 seconds before the first injection into the SPS !

Adding ‘zeros’… 6 Injection sequencing / BCM 6/23/2009 Timing user LHC1 (for example), cycle length 21.6 s Timing users ZERO (no beam, length 1.2 s)  A trick to lengthen the SPS super-cycle without having to regenerate a new cycle with its settings. The ZERO user has no beam, and the power converters just stay at their last value until LHC1 is executed again.. SPS super-cycle

Observations : prepulses… 7  Initially we had no prepulses, because the user LHC1 that we had, was used for the first time for LHC extraction, and the prepulse settings were not correct (fortunately JW had stored references… ) ! >> Extra diagnostics added to the extraction BIS monitoring application 6/23/2009 Injection sequencing / BCM ! Only enable/disable allowed for set !

‘En passant’: prepulse diagnostic 8  Arrival of prepulse (trigger for the kicker) and warning events (trigger charging) can also be diagnosed in the same application. They can be enabled at the kicker level by LTIMs. 6/23/2009 Injection sequencing / BCM Here example of CNGS… Control of LTIMs through those buttons

Observations : debunching-recapture 9  The RF loops that are working on the first injection can be in trouble to capture the beam properly in case of non-nominal RF conditions or ‘instabilities’ in the PS (for example when the intensity is changed …). >> debunching – recapture that populates buckets in front or after the nominal positions. >> RF quality check before extraction crucial !! 6/23/2009 Injection sequencing / BCM First injection End of injection Before extraction The red bunches in front of the first nominal bunch may be swept across the septum (similar to LHC asynch. dump)

Losses on septa 10 Injection sequencing / BCM 6/23/2009 LSS6 : swept bunches with LHC beam LSS4 : beam in gap for CNGS (same effect…) BLMs at TPSG (septum prot.) 5 mGray correspond to loss of ~ 5  10 9 p. ~ 5  p.

11 Injection sequencing / BCM 6/23/2009  Spurious triggers with excessively large readings appear on the TL BPMs in the event of a poor capture due to the filling of intermediate buckets between the nominal 25 ns slots – ‘normal’ under such conditions. Other observations… Bunch/trigger number Position / mm

Other observations… 12 Injection sequencing / BCM 6/23/2009  We initially extracted to the TED TT60 with the cooling switched off. Thank you SIS for stopping the beam in time ( T reaching 60 deg). ¼ of nominal extraction gives a short T spike of ~15 deg.

Summary 13 Injection sequencing / BCM 6/23/2009  Nominal filling was never fully executed, but with the exception of the ‘first batch after empty cycle’ effect everything worked fine.  The features in the timing system that have been spotted should be fixed – to be rechecked.  Prepulse diagnostics improved after the MD. Settings are critical – must define a strategy and hope that the settings are stable for LHC beams (they are for CNGS). Settings group: perpulse + kicker delays (SPS extr + LHC inj)  Beam quality monitor in the SPS before extraction could be critical to avoid sweeping beam over septum and sending batches with significant ‘leading bunches’ into the LHC. Overall very successful – and things become easier to run! But good understanding of timing & RF essential to solve problems !

Information on interlocks, settings and more of extractions… 14 Injection sequencing / BCM 6/23/2009