BI WP13 Meeting #3 2017
29 January 2016
15:09
https://indico.cern.ch/event/628210/
Present: Rhod, Christos, Thibaut, Sotiris, Ye Zou, M. Bartosik, J. Storey, F. Cerutti, A. Tsinganis, A. Lechner, A. Mereghetti
Tracking simulations of beam losses in the HL-LHC triplet (Y. Zou)
Simulation configuration
- Loss case:
- IT partially sees IR7 halo due to misaligned TCTs
- Fully open TCTs (conservative)
- Open TCLAs in IR7 & TCDQ/TCSG in IR6
- Open TCL in Pt 4,5,6
- HL-LHC beam @ 7TeV
- Results
- B1 losses mainly in IR1IT
- B2 losses mainly in IR5IT
- Mainly in H plane
- Visible as spikes in aperture changes - mainly BPM-beamscreen transitions
- Larger crossing angle - more losses
These results passed to FLUKA team for input
Discussion:
- At least 2 order of magnitude less with all collimators at correct position
- Loss scenarios
- Fast losses seen first in collimation region - e.g. crab cavity
- Orbit bump not during collision
BLM response simulations for the HL-LHC triplet (A. Tsinganis)
Simulation of Collision Debris & Losses
- Triplet-D1: Peak power density profile
- Losses, normalised to 35mW/cm3 quench limit
- Main peak - at MCBX corrector behind Q2B
- Corresponds to 4.1E9p/s lost locally è7.36E13p/s global loss rate
- A few seconds of beam life-time or ~80 MW of power lost
- Collimation system dumps on 500kW up to 1MW for a few seconds
- BLMs
- Standard - for quench would expect factor 10 above lumi debris
- Cryo - for quench would expect similar factor above lumi debris
HL-LHC more favourable than current LHC as there is more quench margin between lumi debris & quench limit
- Governed by long term damage to magnets
- Addition of tungsten shielding lowers debris
- These are the changes from the initial predictions of Mariusz
Conclusion:
- Both standard and cryo BLM systems would easily detect losses leading to quench above the lumi debris background
- Losses that could lead to a quench of the triplets would be detected in collimation BLM system way before they reach the quench level in the triplet
Discussion
Cryo BLM Development Status (M. Bartosik)
Irradiation tests
- 18 different Si & 2 diamond detectors @ 4.2K
- Up to 1.9MGy & 6.8E15 p/cm2 (24GeV)
- Decrease from beginning to end of irradiation:
- ~ factor 8 for diamond
- ~ factor 32 for silicon
- Tests in magnetic field (up to 1T) at warm & not irradiated
- Show change in transit time which depends on orientation
- Next step is test in at cold in magnetic field
- Test for various orientations and if possible both virgin & irradiated diamond
Charge collection efficiency in Si (p+-n-n+) & single crystal diamond decreases by factor ~10 after 10^16 protons
scCVD
- Erratic discharges for bias >100V
- Polarisation due to asymmetric trap filling
- Reduction of CCE - can be prevented by switching bias or higher voltage (but this leads to problem 1)
- Charge per particle depends on flux rate
pCVD
- Erratic discharges not seen in 0.5T B field
- Charge per particle independent of flux rate (but half that of scCVD)
- Less prone to polarisation
p+-n-n+ Si
- CCE (300um) ~same as 100V scCVD
- Promising results for 100um sensors
- Polarisation also seen
Need to solve erratic discharge to profit from superior radiation hardness of CVD
ACTION:
- Cryo BLM team to prepare plan for:
- Radiation tests in 2017
- Lab tests with magnetic field at cold in 2017
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