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CLIC Beam Physics Meeting
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Europe/Zurich
6/2-004 (CERN)
Description
Damping ring frequency choice, Update on the booster linac frequency choice, Choice of drive beam decelerator BPM number, Space reservation for the positron spin rotator (via WebEx)
Participants: F. Antoniou, R. Corsini, B. Dalena, S. Döbert, J. Esberg, A. Grudiev, B. Jeanneret, M. Jonker, A. Latina (via WebEx), E. Marin, Ö. Mete, Y. Papaphilippou, J. Pfingstner, D. Schulte, J. Snuverink, G. Sterbini, F. Stulle, I. Syratchev, F. Tecker, A. Vivoli
A.L. presented some considerations for the location of the spin rotators and a first layout for the e- spin rotator. Locating the e- spin rotator just after the damping rings does not imply any spin dilution since its direction of motion is parallel to the main linac. Locating the e+ spin rotor there would imply a loss of 2.2% of polarization since its path is anti-parallel to the direction of the main linac. Nevertheless, he proposed to locate both spin rotators after the damping rings since particle energy lower which should simpify design. This was accepted to be baseline for the CDR. Moving the e+ spin rotator to the tunnel will be described as an alternative. F.S. asked if it would be possible to make the central arc isochronous. A.L. and F.S. will work on this.
A.G. gave an update on the comparison of 1GHz and 2GHz RF for the damping rings. The 1GHz option is a lot closer to existing RF for rings and thus imposes less risk. The 2GHz option would be more power efficient. The study will be continued.
Y.P. showed that 1GHz would be beneficial for beam dynamics in the damping rings. But neither is perfect and both need more studies. He proposed to describe both options in the CDR at the same level of detail. He also showed a shorter lattice which reduces space charge tune shift. D.S. recognized that for the 1GHz option increasing the repetition rate to 100Hz and having 400ns long pulses would not be possible since the lattice would be too short. Regarding the required bunch recombination D.S. showed confidence that this should be possible. Hence, for the moment 1GHz should become baseline and 2GHz will be described as an option.
S.D. showed first results for 2GHz cavities for the booster linac. He started calculation HOMs and asked up to which frequency these are required for beam dynamics simulations. D.S. answered that an analytical model might be used for frequencies above 10GHz. S.D. asked which distance e- and e+ beams will have. D.S. said it must be evaluated which distance is required for beam loading compensation. The first bunches should be stable enough in energy to avoid spoiling the performance of the energy feedback. D.S. and F.S. will provide required information. 2GHz will be baseline for the booster linac. 4GHz will be described as an alternative.
D.S. discussed the required number of BPMs in the decelerator. Studies show that performance is strongly reduced if too few are used. Equipping every second quadrupole with a BPM seems to be minimum. Some margin is gained by using 2 out of 3 BPMs. This will be used as baseline.
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