Status of commissioning with beam (S. Gilardoni) - Discussion

Roland asked if the fluctuations could come from POPS or if POPS had made the situation worse. Simone replied that the data were taken when POPS was not optimized but can’t comment more. Jean-Paul commented  that the feedback system is the same (for POPS and for the rotating MPS) so no difference should be seen between the two. The only difference might come from the noise, the MPS has a 50 Hz noise whereas the POPS has noise line at some kHz.
Oliver asked about the remnant field that could be present at injection. Simone confirmed that a remnant field is present at injection both of dipolar and quadrupolar type. However, no measurable difference could be observed from super-cycle to super-cycle. In any case, the sextupolar and octupolar components cannot be measured, yet. An improved magnetic measurement system is foreseen for the coming winter technical stop.
Gianluigi suggested performing measurements with an MTE user located after a 26 GeV/c cycle in order to go to have the maximum hysteresis effect from the saturation of the MMU. Simone answered that an idea was to cycle the figure-of-eight loop before the MTE cycle.
Roland commented that the capture process should be very sensitive to perturbation at the beginning of the process. Simone confirmed that indeed the beginning of the capture process is crucial. This was confirmed also by wire scanner measurements performed right after resonance crossing: from the shape of the profile it was possible to infer whether the trapping was good or bad.
Olivier asked if an energy error is seen at injection due to the remnant field. Simone replied that due to the radial loop we are put back in the center of the pipe. However, it was checked that no particular activity was on-going on the RF loops at 14 GeV/c significantly different from cycle-to-cycle, thus indicating that no energy error is present at 14 GeV/c.
Massimo commented that 2 GeV/c tests were proposed to have an even simpler situation, for example at that energy we don’t need to use the pole-face-windings and were the machine is very linear.