Measurements’ analysis (A. Lachaize) - Discussion

Jean-Paul argued that the MTE sextupoles are assumed to be stable in current, but that maybe they are not in remnant field. Simone answered that it is the reason why the chromaticity measurements (scans in energy) are not “centered”, but are done with an offset to probe the sextupolar component (in any case, these magnets are used only by MTE and hence, they are always on the same hysteris cycle. Therefore, they should provide a very reproducible field).
Massimo commented that next to the origin the measurement of the higher-order field components is rather difficult. This is why the beam is indeed displaced to rather large amplitudes (up to ±20 mm) to enhance the sensitivity of the measurement to the high-order components. Around these points the energy scan is then performed to measure the non-linear chromaticity.
Jean-Paul commented that the 24 kHz structures seen by Antoine are at a multiple of the 6 kHz frequencies of switch power converters used by the pole-face-windings. This should be looked at in more details.
Simone mentioned that tests in three-current mode are planned. However it is commented that due to power converter changes that will not restore exactly the same situation back to when the three-current mode was the only one in operation.
Roland asked if it is possible to close the bump for the core and for the islands. Antoine replied that we can try as there are six independent bumpers.
Gianluigi asked what is the nominal amplitude of the islands at extraction (as it was showed that the fluctuations are more important for the outer islands, the fluctuations then being amplitude dependent). Massimo answered that the parameters used during the measurements are realistic, except for the tune ramp that is slower in the nominal MTE case.
Jeroen asked if bunch length changes were seen during the tune ramp. Antoine answered that it was not the case.
Simone commented that the extraction is done around 20 -30 mm, for a horizontal tune of 0.255-0.256. Therefore the oscillations (“resonance”) seen at 0.26 will be possibly not crossed. This would depend on the tune line and it will be investigated.