injection problems: week 41
DESCRIPTION
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 8 th after 248b fill. - PowerPoint PPT PresentationTRANSCRIPT
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Injection problems: week 41
C. Bracco, W. Bartmann, B. Goddard, V. Kain, M.Meddahi, V. Mertens, J.
Uythoven
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• Obstacle in MSI• Problem with 800 MHz in SPS• Other longitudinal problems leading to losses
at injection
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Started Fri 8th after 248b fill
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4
Problem localised to MSIA-MSIB transition by beam losses
B.Goddard et al.
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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
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…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
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→ Mis-steer injection: match oscillation fromline with bump in the LHC Horizontal
Vertical
Bottleneck
Bottleneck
LHC
LHC
1 unit bump
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Orbit bump during injection.
Removed before rampHorizontal
Vertical: 1 unit
Injection oscillations afterwards after matching
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TCDI Collimators set around new Trajectory
24 bunches
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8 Bunches Injection
MSIB
MSIA
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24 Bunches Injection
MSIB
MSIA
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→ Fill afterwards: > 1032 luminosity
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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
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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
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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
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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
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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
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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.
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Other things
• Abort gap keeper: allowed bucket numbers changed.– Last allowed bucket 31140