Minutes of the CLIC Meeting - 22 August 2003
Agenda:
|
Discussion of CLIC Beam Dynamics items.
What do we need to do to establish CLIC feasibility?
How should we proceed with the work?
|
Speaker:
|
Daniel Schulte
|
Daniel presented a list
of different beam dynamics topics to prove the feasibility of CLIC in the
three work areas of
- Drive beam complex
- Main beam complex
- CTF3
copy of his transparencies (pdf format)
He attributed a ranking to the various points depending
on how critical he personally estimates the item for CLIC, from one to three
stars with increasing difficulty but independent of the amount of work
that is still required.
The main points were (with the according comments):
- Drive beam:
- Drive beam timing and intensity ***
Due to the 1 ‰ energy error limit in the main
linac caused by the final focus acceptance, the overall phase error has to
be below 1/4° at 30 GHz. In addition to timing issues, this imposes
a tight intensity tolerance, since intensity errors cause energy errors
due to the beam loading and these transform into phase errors in the bunch
compression. Hence, losses have to be kept constant.
There are some ideas about cures, f.i. the intensity
could be adjusted by a feed-back for the combiner ring current.
-
Drive beam losses ***
Scenarios for permanent and accidental beam losses
have to be identified and investigated.
-
General beam physics *
The fast beam ion instability requires a 10-10 vacuum for the
transfer lines which might be problematic in the decelerator in the presence
of RF.
- Main beam
- Damping ring **
Imperfections, electron cloud and fast ion instability
have to be included in the simulations.
- Collimation system **
The pre-linac collimation system is not yet designed
but should be easier than the beam delivery system (BDS) collimation and could
be potentially copied from NLC.
- Line for the spent beam *(*)
This line is not yet designed. It will have positive
and negative charges and possible instrumentation should be identified.
- Emittance measurement station **
If it cannot be included in the collimation section,
this could be of the order of 2 km long.
- Diagnostic sections **
- Interaction point **
-
Polarization is not included but could be possibly
measured by the experiments through a well known process.
- Luminosity monitor ***
This is the final signal to tune the machine. A Bhabha
measurement would be too slow. Coherent pairs (which are not proportional
to L, dependent on field) dominate the emerging particles but could be used
for tuning.
- Overall tuning and Luminosity ***
An overall modelling is needed to evaluate the effects.
It has to be verified that the time needed for tuning is short enough compared
to dynamic changes of the machine.
- Beam physics matters ***
Multi-bunch effects and electron cloud have to be
modelled.
- CTF3
-
We need to think about tests for strong model predictions
and BENCHMARKING!
-
CSR in the combiner ring: this is an excellent test
bed since CSR should be almost independent from energy.
-
CTF3 should be valuable test bed for feedbacks.
-
CTF3 as a test for timing stability? It will be certainly
interesting but eventually hard to extrapolate. So there is discussion about
measurement possibilities needed.
-
Multi-bunch issues: beam-loading compensation could
be probed by single bunch probe beam with timing changes and even by direct
RF measurements.
-
Drive beam decelerator: This needs a strongly instrumented
measurement line to be able to extrapolate the 35 A beam current to the
four times higher current at CLIC.
This should have a very high priority!
In the discussion, it was suggested to hold a few dedicated
CTF3 working group meetings to discuss ideas about the benchmarking experiments.
For this huge amount of work in the various areas, a priority list should
be established to proceed systematically in the view of the very limited manpower.
A planning for people dealing with the
different topics should be made in order to clarify how much can be covered
with the allocated resources.
Back to the CLIC
meeting Home page
Frank
Tecker - Last updated 26-08-2003