Hans gave a short introduction, motivating the present parameter
discussion by recent progress (structures, DR, fully loaded
acceleration, physics report) and less advancement in other areas.
He listed the following open issues:
long range HDS wakefields
7 λ bunch spacing corresponding to 4.29 GHz, which is not a
subharmonic of the drive beam bunch frequency
the possibility of having e+/e- simultaneously in each linacs
no integrated DR to IP simulation, no precise emittance growth
estimation
the reduced pulse length cannot easily be made with the present
CTF3
Daniel stressed the importance of the main linac beam dynamics,
including misalignments and mentioned the drive beam phase stability.
The possibility of having both e+ and e- in the two linacs was
discussed. This would imply to have two detectors that split the
luminosity between them, having half the background per event. It would
enable both BDS to be tuned in parallel and linac tuning during the
operation. Daniel showed some sketches showing different possibilities.
Having mixed e+/e- linac would have the advantage of twice the bunch
spacing in the pre-accelerators and DR but would require RF deflectors
to combine the bunches. Even without mixed running, one could
interleave the bunches in order to reduce the RF frequency of the DR by
a factor 2. This mode of operation would still be OK for the given
damping time.
It was suggested to adapt in the baseline an interleaving without
mixing to allow for half the RF frequency in the DR.
After some discussion, it was decided to fix the bunch separation to 8
cycles. This implies that Alexej has to run his optimization again and
the other parameters (DR, PETS, drive beam current) will follow
subsequently.
Maxim showed the DR beam parameters for a frequency of 3.75 GHz, 2.36e9
particles with 10cm wiggler period. For 0.6% betatron coupling, the
normalized emittances would result in: horizontal 550 nmrad, vertical
3.3 nmrad, and longitudinal 4200 eVm (for Vrf=2.3MV).
The vertical emittance from the DR of 3.3 nmrad would allow for a
budget to increase to 10 nmrad.
For the horizontal emittance, an increase of 20% above the DR result
can be budgeted in the linac.
Daniel mentioned that the BDS increases the horizontal spot size
significantly, caused by uncerrected chromaticity and the collimation
section. There could be room for significant improvement there. The FF
optimization is not very clear, though it was optimized and β* is
adjustable.
Finally, after optimization of the parameters, the linac repetition
rate will be adjusted to reach the desired luminosity.
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CLIC meeting Home page Frank
Tecker - Last updated 7-12-2004
