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CLIC Implementation Meeting: Design
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Europe/Zurich
6/2-004 (CERN)
Participants: Alexej, Konrad, Licie, Feno, Juergen, Raul, Fabien, Michele, Yanliang, Andrea, Daniel, Ryan, Edu, Philipp Roloff, Walter, ?
Philip presents: Physics at \sqrt(s) < 350 GeV
Daniel: Run at 91 GeV: should it be for testing and calibration, or for long-time runs? The solution might be very different for the two cases. If it is for long runs, it is more challenging, but one could consider some options: bypasses, or removing structures, etc.
Lucie: Could you please envisage a few scenarios, and give an estimate of the two luminosities? Performing long runs at 91 GeV could be useful, and it would be better to consider it. Besides, this evaluation would also provide some useful indications for the EU strategy inputs.
\sqrt(s) = 161 GeV is useful to measure the mass of the Higgs at threshold. It is not a crucial energy stage.
\sqrt(s) = 240/250 GeV Higgsstrahlung could also be measured at 350GeV and 420 GeV. No strong argument to have this.
Conclusion: \sqrt(s) = 91 GeV is the most interesting energy < 350 GeV and should be considered.
D: A rough estimate is that running at 91 GeV might give 1/4 of the nominal luminosity. This corresponds to roughly 0.4 fb^-1 per year. Philip judges this already satisfactory, but they will provide a feedback. Philip and Lucie will need to define the luminosity needed for calibration.
Reno Andrianala: Higgsstrahlung and Beam size choice
Feno presents a first evaluation of the optimum value for the trade-off between luminosity and beamstrahlung for the cross section measurement of the Higgsstrahlung process at CLIC. He verified that the choice of the actual beam parameters at CLIC is confirmed to be reasonable from the physics analysis point of view. He also compared with the ILC case, verifying that the results are consistent with the full simulations of ILC at 350 GeV. The precisions achieved by CLIC and by ILC are almost the same.
Alexej: perhaps one could then increase the horizontal beam size, as it does not affect so much the prevision of the measurement. Could this help relax some tolerances? Daniel: Not really. But perhaps one could try to reduce the horizontal beta function.
Andrea: RTML
A consolidation of the static performances has been performed on the 380 GeV parameters set. Work is in progress, as some machines don’t converge. A revaluation of the average RF power consumption results in significantly smaller numbers than those quoted in the CDR: ~5 MW rather than 25 MW. But the problem of the train spacing must be addressed. Alexey asks to revaluate the longitudinal beam stability requirements from the RTML to the Damping Rings.
Daniel: Main Linac Lattice Design new parameters.
At 380 GeV, using the same strategy as the CDR Daniel found that the modules are now slightly longer because the accelerator structures are longer (33 cells). Only 3 types of modules (which means 2 types of quadrupole magnets are necessary), w.r.t. 5 for the 3 TeV energy stage. Old module length of 2.010 m, is now 2.343 m. The required quadrupoles lengths are: 43 cm magnetic length, and 101 cm. The new lattice optimization confirmed the main design choices of the original design.
If PETS and AS are rigidly connected, Daniel points out that the drive beam quadrupoles should be supported independently. The avoid the the alignment of the main linac structures moves the DB too much. Walter suggests that the drive beam quadrupoles could be solidly fixed on the ground, whereas the PETS should be rigidly fixed with the main linac structures. This would allow to avoid the bellows from the RF network, which would simplify significantly the RF distribution.
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