Injection problems: week 41

C. Bracco, W. Bartmann, B. Goddard, V. Kain, M.Meddahi, V. Mertens, J.

Uythoven

• Obstacle in MSI• Problem with 800 MHz in SPS• Other longitudinal problems leading to losses

at injection

Started Fri 8th after 248b fill

4

Problem localised to MSIA-MSIB transition by beam losses

B.Goddard et al.

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

G. Arduini 13/10/2010

Circulating beam

Injected beam

J-M. Dalin

…Drawing picture of obstacle

old old

new new

High losses

No losses

High losses

No losses

→ move beam in septum

-4 mm Vertical+1 mm Horizontal

monitoring losses at the MSIA, MSIB, MQ5, TCTH.4L2 and TCLIB, with pilot bunches

On Wednesday: Horizontal & Vertical Scan @ MSI

→ Mis-steer injection: match oscillation fromline with bump in the LHC Horizontal

Vertical

Bottleneck

Bottleneck

LHC

LHC

1 unit bump

Orbit bump during injection.

Removed before rampHorizontal

Vertical: 1 unit

Injection oscillations afterwards after matching

TCDI Collimators set around new Trajectory

24 bunches

8 Bunches Injection

MSIB

MSIA

24 Bunches Injection

MSIB

MSIA

→ Fill afterwards: > 1032 luminosity

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

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

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

Losses on rising edge of kicker waveform seen by LHCb

MKI8%

0.0

20.0

40.0

60.0

80.0

100.0

82000

82500

83000

83500

84000

84500

85000

Delay (ns)

Defl

ecti

on (%

)

2010

LHCb signal at -700 ns

93%

7%

Lower TDI jaw at 6.8 sigma (12%)

Upper TDI jaw at 6.8 sigma (88%)

Uncaptured beamon LOWER TDI jaw

Satel l i tes on UPPER TDI jaw

LHCb s ignal at -100 ns

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 hoursMissing diagnostics…SPS surveillance, and try to get signals from LHCb

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

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.

Other things

• Abort gap keeper: allowed bucket numbers changed.– Last allowed bucket 31140