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v3.3.5-pre
5th CLIC-ILC BDS+MDI meeting
Crab Cavities, Graeme.
12 GHz for synergy with main RF and lower voltage.
Beam aperture (iris radius) is 5mm.
Many high order modes to be damped. Choke-mode damping
is also required. Best damping is still far from specification.
Another option is to introduce detuning to decohere the wakes.
Waveguide dumped and choke mode detuned options are not far from specs.
The lenght of the CC (16celss) is ~ 20cm. Some tolerances were too
pessimistic.
CERN RF contact is Erk Jensen.
Updates on a new tuning technique
Andrea Latina
10 mum misalignments are assumed. Synchrotron radiation is considered. 100000 particles is required to minimize numerical effects. Magnets are sliced in 50 slices. In previous presentations it was shown that the achieved sigmay is 30nm after optimization and horizontal is 1250nm.
Actions so far: improve the response matrices and the target trajectories.
1) improve optics scaling, energy change computed and updated at all elements.
2) When a single particle is tracked the SR is the average value and not the random usual calculation that would be wrong.
Improvements are very modest after this modifications.
Might the problem be related to energy spread?
Without SR and dp/p=0 final sigmay=1.4nm ! Improvement!
With SR and dp/p=0 final sigmay=20nm, also improvement.
SR seems still to be the largest problem.
Beam dynamics with CCs
Ian Shinton
CCs reduce the luminosity by max 10%. This was already studied in ILC by Andrei Seryi.
First thing tried was to approach cavity to sextupole without any real improvement.
There is a difference with the ILC case, in CLIC there is no y' spread. To be followed up with Andrei Seryi by email.
Collimator stress
Luis Fernandez (Deepa talking)
Simulating for longer time shows some problems but impact depth was too pessimistic 365 sigmas. A more optimistic impact at 165 sigmas gives 5mum deformation. Is it OK?
Measuring how field quality changes when a dipole is run at very low fields.
Cherrill Spencer
Old SLAC dipole for FACET. Water cooled. Gap is over 2cm. Pole is 5cm wide.
It normally runs 116 Amps. 0.5 Amps gives 55 Gauss. What is the shape of the field in these
two circumstances. Stretched wire is used for moving the field. The field drops down towards
to the edge of the pole. Fields is not a pure dipole but contains higher order aberrations.
To get 55 Gauss the trim coils has to be used. The relative field quality is almost the same at all
powering. So there are no worries concerning the field quality for low fields. Although for such low fields the dipole could have no iron.
With another example at 72 Gauss the sextupole field increased.
Tolerances from simulations are 6 10^-4 units, so looks good.
In ILC going from 100 Gauss to 50 Gauss was seen as a concerned, we should understand why.
From these measurements there is no real concern.