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v3.3.5-pre
News
CDR BDS section "Live" web page available at:
http://clicr.web.cern.ch/CLICr/MainBeam/BDS/CDR/TEX/
Any feedback is most welcome, to be sent to Deepa, Andrei
and Rogelio.
Collimation wrap up
Spoiler flat length needs to be justified since 0.05 radiation lengths seemed too short
in previous meetings. From first calculations the flat length of the betatronic spoiler must
be > 0.1 X0. For the energy spoiler this should be > 0.02 X0.
Simulations confirm the survivability of the absorber. Studies for the particle deposition
along the BDS are on-going.
Transverse absorbers should not be made of Be since they are sacrificial.
FLUKA simulations
With 0.01X0 an impact of the beam is very safe, no risk of fracture or deformation.
For 0.05X0 beam impact will cause deformation in the 0.1% level but not fracture.
Rigid supports can cause peaks of stress, problem. This is under investigation.
Muons
Muons are a potential problem.
Halo is hard to predict but the minimum level of halo comes from beam gas scattering.
Safety factor is usually included.
How worried are detectors about muons?
Helmut proposes to reduce muons only in case of problems. Leave it open in the CDR,
preparing the space and the infrastructure.
Lau mentions that radiation protection in the "parked" detector might be a problem.
Phil mentions that one issue in the past was muon ionization from axial muons
for the hadronic calorimeter. This is not a catastrophy but hampers precision calorimetry.
Alternative muon suppression
Swapped layout (energy-transverse collimation) reduces the background to 40% -> modest reduction
(IPAC10). Daniel: This does not include muons from the energy collimation, which in the swapped case
would make it worse.
Magnetized muon suppressors: outer radius 55cm, inner radius 1cm, B=1.5T.
Assuming spoilers are placed ~100m from IP. Total length of spoilers is 83m
cause times 0.1 reduction of the muon flux. Space is available.
Location and other parameters show margin for optimization.
Lau guesses that with some optimization a factor 0.01 could be reached.
ILC spoiler system reduction was much larger and cost too (to be followed up).
To be followed up in next meetings.
Phil: 1% halo tail in SLC was a surprise.
Marco: 50 muons per event would start degrading the reconstruction. This is both a
problem for occupancy and reconstruction.
Daniel: assuming the same vacuum as in the linac the situation would already improve
by a factor of 10.
AOB
Andrei is already in UK.
Next meeting in 2-3 weeks. Possible topics: collimator stress, Crab cavities, FFS tuning, low field magnets...