1st Run II FiDeL meeting

Wednesday 22 Apr 2015, 09:00 → 10:30 Europe/Zurich

 

Date: 2015-04-21

Place: 865-1-B03

 

Presents: Matteo Solfaroli Camillocci, Mariusz Juchno, Ewan McLean, Ezio Todesco, Per Hagen, Frank Schmidt, Vittorio Remondino, Rogelio Tomas Garcia, Mike Lamont,

 

Precycle strategy [M. Solfaroli Camillocci and P. Hagen]

Matteo presents the new implementation of the precycling strategy for the LHC run II. This includes both the precycle and the ramp down, aiming at minimizing the time needed to bring the machine ready for injection. Dipoles follow the same pattern as for Run I, with a PELP and a 10 A/s ramp up and down to 100 A (without pre-injection plateau). The flattop plateau is at 600 s in the precycle. New time for precycle at 6.5 TeV is 3100 s, and 1300 s for ramp down. The work aimed at having the other magnets in the shadow of the dipoles. A faster ramp down for the quadrupole (including the inner triplet) circuits has been obtained. Main implications could be a larger tune decay induced by faster ramp down in the quadrupoles.

Matteo also summarizes the changes in the FiDeL implemented by Per and underlines that the differences found in the generated settings are coherent with the expectations.

 

Chromaticity during ramp - [M. Lamont]

Mike shows the first results of chromaticity measurements during the ramp to 6.5 TeV. First ramps have been done with the snapback correction used for 4 TeV. Data clearly show that the snapback is undercorrected as expected. A series of measurements (naked ramp, without any correction of snapback) is foreseen to tune the field model in the new conditions at 6.5 TeV.

 

Status of the LHC optics - [R. Tomas Garcia]

Rogelio reviews the measurements of the beta beating of the LHC at injection and at 6.5 TeV, before squeeze. At injection beta beating is of the same size as in 2012 (20%-40% peak). After global corrections, it is brought to ~5%. At 6.5 TeV, beta beating before correction is a bit better than in 2012 at 4 TeV, with a peak of 15%, and average of less than 10%. 

 

Bare tunes in the ramp - [M. Juchno]

Mariusz presents the reconstruction of the bare tunes during the ramp. The pattern is similar to the 2012 pattern in the initial part of the ramp for beam 2, suggesting a precision in tracking b2/b1 of 15 units, as already observed. Above 1 TeV the error reduces, and above 4 TeV the bare tunes are stable, suggesting that the errors in the saturation component of the model are well below 5 units.  There is an anomaly in Beam1, showing a negative drift in the horizontal tune of 0.08 from 3 to 6.5 TeV. Mariusz shown that this drift is close to be linear with energy, and that if this component is removed both beam behave in  similar way, as in run I. This drift cannot be given by errors in modelling b2 or b1 since they would affect both horizontal and vertical tune in similar way. The pattern seems to point to a feed-down effect of sextupole with horizontal misalignment. Further investigation is needed. Matteo confirms that tune feedback is more problematic for Beam1 during the ramp since it has to correct a large offset.