Attendees:
X. Buffat, A. Grudiev, S. Hegglin, G. Iadarola, K. Li, K. K, L. Mether, E. Metral, A. Oeftiger, G. Rumolo, M. Schenk
Overview of the project - current status, questions and asking for suggestions and feedback.
Brief update on the status of the project and how an RFQ is supposed to work more effectively compared to equivalent octupoles in the LHC.
EM: Electron cloud in quadrupoles in the LHC appear to give comparable tune spreads as expected from octupoles or RFQ. The interplay should also be studied at some stage.
Motivations were formulated, simulations presented and a study case in the SPS was identified.
EM: Interestingly higher order chromaticities were included in the simulations which give good agreement with measurements in the SPS – analytical computations do not include these effects but still give a good agreement. To be noted and perhaps looked at in the future.
Tasks and goals were presented for the SPS study case – demonstration of feasibility, robustness and identification of other unexpected effects.
Discovered 3 regimes of RFQ strengths – the coherent regime, that regime of stability and the regime of incoherent losses.
There is the suspicion of Sychro-Betatron Resonances (SBR) induced by the RFQ. Simulations that targeted to investigate this suspicion were presented.
EM: If SBR are an issue, we need to be very attentive in the LHC since this could be a limitation. AG: The required tune spread is a lot lower than Qs so we could be on the safe side. 6 cavities will never be able to create a Qs spread larger than Qs.
GR: the coherent part can be trusted – the incoherent part is tricky to deal with numerically.
EM: when Qs is bigger the situation could become worse. Can we redo this case with Q26 which has a lower Qs?
We should get an idea on the evolution of the resonances with the number of macroparticles and show that the incoherent losses are strongly dependent on the numerical parameters (i.e. macroparticlenumber)
We can make the proposal for the SPS case but keep in mind potential issues due to SBR.
Even with an overlap of the regions of coherent instability and incoherent losses, we should be able to distinguish the two regimes via observations in the machine. They are expected to show different signatures.
A section meeting will be scheduled for this month to review the obtained results and proposed strategy. This will be followed by an internal review to present this proposal to the management.
Before end of December in parallel internal review.
The impedance of the RFQ itself has not been included. It should be modeled rather well by the impedance of a 400 MHz LHC type cavity. The impedance is expected to have a negligible impact.
Round table:
The development of multi bunch has started a couple of days ago. First results from generating and tracking a multi-bunch beam were shown.
Non-linear kicks from sextupoles and octupoles is planned to be included into PyHEADTAIL in the near future.
KL, 02/11/2015