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3rd RunIII FiDeL meeting
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Europe/Zurich
Date: 2020-03-10
Place: everywhere
Presents:
R. Tomas Garcia, J. Wenninger, M. Solfaroli Camillocci, L. Fiscarelli, J. Dilly, E. Todesco, E. Maclean, P. Hagen, P. Skowronski (all present with remote connection)
Recall of the magnetic model implementation in LSA [M. Solfaroli]
Matteo recalls the implementation of the magnetic model in LSA. A subset of the database of FiDeL parameters REFPARM is copied on the LSA side. This contains the values relative to the circuit, the TF and few multipoles, i.e. whatever is needed for operation.
Note that REFPARM contains not only the parameters of the individual magnets, but also the value for the circuits, so it has been periodically updated every longshut down by Per to account for the magnet replacement. It is a negligible change in the settings, but it has been done to keep the consistency of the full system.
The dynamic part is generated separately from the static, with a server that uses the FiDeL coefficients, and access the information about the previous run parameters on LSA (via the sequencer).
During the discussion, Rogelio asks to have the results of WISE for next run, also including 7 TeV energy. Rogelio also expresses the concern about the differences in b2 from WISE between the 2011 and 2015 releases. Both aspects will be discussed in a dedicated talk.
11 T magnetic measurements towards FiDeL, episode II [M. Solfaroli Camillocci and L. Fiscarelli]
Matteo gives the impact on the machine settings for the case of one 11 T unit installed (two 5.5-m-long magnets). The caveat is that these estimates are based on the measurements of two apertures of one prototype.
As it is well known, the 11 T needs a trim with a maximum current of about -200 A to compensate for a maximum kick of 0.6 T·m at half of the ramp. Jorg will discuss the matters relative to the need of the trim in early phase of commissioning in a dedicated talk.
There is a variation of about 20 units of b2 during the ramp, that produces about 0.002 of tune variation. This could be corrected with the tune correctors (implementing the variation of b2 in LSA or, or left to the tune feedback) or with a local correction, using the close-by Q9, as proposed by Massimo. The local correction is relatively easy to implement, but it would generate a singularity in the control system ; as a consequence, it should be evaluated whether this solution is needed or not. The value is small but not negligible.
There is a 1 unit of chromaticity coming from the b3 dependence on current soon after the beginning of the ramp. Also this effect is small but not negligible and could be corrected via lattice sextupoles or via spool pieces.
All other effects are negligible (decay at injection and at flattop, etc.).
The b4 issue [E. Maclean]
Ewen reports about recent development in the b4 issue, i.e. the discrepancy in CMS between computed and estimated settings of the b4 correction in the interaction regions (slide 4).
In the past weeks, simulations have been done splitting each contribution to see how the corrections build up. The MQXA systematic b4 gives the main part, i.e. 0.8 m-4, positive on left side and negative on right side, for both IR1 and IR5. This is about 30% of the maximum correction strength. When the MQXB are addded, a 20% change is induced, presenting a systematic offset with respect to beam measurements. Finally, when the beam screen contribution is added, IR1 computation agrees with measurements, but IR5 gets even more distant. The beam screen contribution has different signs in IR1 and IR5, due to H/V orientation of the beam screen (EDMS 392308). If the beam screen contribution had the same sign of IR1, the match would be good also for IR5.
A wrong installation of the beam screen in IR5 can be obviously excluded. Ezio is checking the simulations with B. Auchman. The saga continues.
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