Minutes of the 30^th WP2 Task Leader Meeting held on 27/06/2014

Present: G. Arduini, O. Brüning, M. Giovannozzi, E. Métral, E. Todesco, A. Valishev, A. Wolski, Y. Papaphilippou

Minutes, Follow-up of Actions, General Information (Gianluigi)

Minutes of the last meeting:

• There were no comments to the minutes of the last meeting

Follow-up of actions:

• Elias has provided the list of BPMs in order of increasing contribution to the impedance. Riccardo to complete the priority table of the triplet BPM taking into account impedance considerations in the Minutes of the meeting held on 23^rd May 2014.

• Preliminary verifications made by Riccardo indicate that the proposed aperture of the TAS (27 mm radius circular aperture is consistent with the injection optics with a b* of 6 m). This should be verified once the criteria used for aperture calculations at injection are revised in order to validate injection optics. Massimo mentioned that this activity is ongoing and R. Bruce is following it up. Action: Roderik to report on that once this work is completed.
• Tatiana will review the PACMAN effects for HL-LHC scenario on 15/08/2014.
• Yannis and Alexander will analyse and benchmark luminosity evolutions with SixTrack and LifeTrack respectively.
• Impedance team will analyse the expected effects of the crab cavity impedance in the SPS and whether those effects will be measurable. After the meeting Elias sent a link to a presentation made by Benoit at the Crab Cavity workshop at BNL (https://indico.cern.ch/event/269322/session/11/contribution/57/material/slides/0.pptx). Task 2.4 will follow-up on the possible tests and measurements that can be done in the SPS to benchmark simulations.
• Ezio will transmit an updated Q4 error tables based on the current MQYY design to replace the existing one extrapolated from the existing MQY field quality. (Done after the meeting, the table is ready for tracking).

Options for D2 and Q4 orbit correctors (E. Todesco)

Ezio presented an update on the design options for the D2-Q4 correctors. He analysed a case for 4.5 Tm integrated with 105 mm aperture and 194 mm separation. Riccardo reminded (see PLC talk 29/4/2014) that 100 mm and 194 mm separation is an option acceptable for aperture considerations. The main issue is the cross talk between apertures due insufficient iron in between the aperture. 3 T operation would require 75 mm of iron instead of 30 mm available. In this configuration the cross-talk results in dependence of the transfer function between the two aperture current values and poor dynamic aperture. Several options were presented with the field quality degradation resulting from opposite sign of vertical field (the horizontal case is slightly better). Only b3 is quoted but other multipole imperfections are present with about the same order of magnitude:

• 3 T, 1.5m, 3.2 kA
  • (V,-V) main field =>b1=12%, b3=200 unit,
  • (V,H) main field -> A1=+4%
  • (V,0) main field -> A1=0.03 T  in the other aperture
  • (H,0) main field -> B1= 0.08 T in the other aperture
• 2 T,  2.15 m , 2.2 kA, , (V, -V) operation =>  b1=5%, b3=100 unit
• 2.5 T,  1.8 m
  • (V,H) main field -> A1=+2%
  • (V,0) main field -> A1=0.01 T  in the other aperture
  • (H,0) main field -> B1= 0.03 T in the other aperture
• Nested coil at 2.1 T, no crosstalk, but challenging magnets 65 cm more per magnet
• Staggered correctors, no crosstalk, easy, but double the length

While the transfer function error could be dealt with a two-variable Fidel model, the field quality issue could not be recovered in other ways.

From the discussion it was concluded that the following options should be further investigated:

• Staggered correctors at higher field (6 T);
• Nested correctors with 3 T field taking into account that the requirements for the powering in the two planes are not symmetric. The aperture can be reduced to 100 mm;
• Study the effect of a reduction of the magnetic field and aperture to 100 mm for the double aperture correctors.

Action: Ezio.

It must be noted that the multipolar field errors integrated over of the set of 4 correctors should remain much smaller than the integrated multipolar field errors of the D2 therefore the field quality of the correctors should be comparable to that of the D2.

Massimo asked whether, in the case of a staggered installation of the correctors space could be found for the installation of spool pieces that could be used for the correction of the D2 field errors that are not yet compatible with the requirements. This should be investigated. Action: Ezio.

Ezio asked the operating scenario of the correctors that were given in the following talk.

HL-LHC V1.1 – Update on optics (R. De Maria)

Riccardo presented the impact on the recent hardware integration exercise on the baseline optics as well as the other accumulated changes with respect to HL-LHCV1.0.

The following points were discussed:

• New TAXS aperture, no impact on present injection beta* (6m) however the TAS represent the aperture bottleneck in the straight section of the IR excluding collimators, therefore being the limiting factor for the lowest injection b*. New parameters for aperture margins calculations at injections are under study and will be used for a final assessment.
• The layout of the TAN-D2 region is still not completely consistent due to the need of keeping the absorber elements at the same location of 1.0 and the introduction of vacuum valves and displacement of the cold mask outside the D2 cryostat, but it was felt that:
  • the necessity of the D2 mask needs to be demonstrated
  • thicker TCL jaws could be possible
  • the possibility of installing a cold mask in the cryostat should be studied.
• The number of crab cavities has been increased from 3 to 4 per beam per side per IR, collision optics has been optimized to increase the b function at their position and to enhance the kick of the cavities reducing the required voltage required to compensate the crossing angle of 590 murad from 12.3 to 11.6 MV.
• The D2 – Q4 correctors have been specified to 4.5 Tm.
• Q5 in IR6 is implemented using a 2×MQY+3×MCBY assembly type (i.e. two cold masses are installed in the same cryostat similarly to what I done inIR2/8). However a MQY+MCBY type in addition to the existing one could also be used. Both solutions are acceptable but the first one is preferable. Action: Ezio to clarify whether the first option is feasible.
• The main sextupole in Q10 (4 2-in-1 assemblies) are still needed for a pre-squeeze optics to a b*=44 cm. The absence of the sextupoles results in in a degradation of the dynamic aperture and optics flexibility in IR2,4,6,8.
• Following a request from Ezio the following parameters have been agreed for the Q4 (MQYY) magnet: 440 T/m×m and a maximum gradient of 115 T/m. These parameters will be implemented in the new layout/optics

Riccardo will send an e-mail to all the WP leaders once the optics/layout is available indicating were the optics and corresponding Twiss files are available. This should happen in the coming week. Action: Riccardo.

Gianluigi reminded the Task Leaders that the deadline for delivering the deliverable reports is the end of October. The draft reports should be sent to Gianluigi before 15^th October and possibly earlier as we will have the Hi-Lumi general meeting in Japan from 17 to 21 November.

Ezio mentioned that first estimates of the effect of the fringe field of the triplet quadrupoles have been done and will initially be implemented with integrated multipole kicks and more accurate model as soon as tracking maps will be available.

Updates from Task Leaders – M. Giovannozzi, E. Métral, O. Brüning,  

Task 2.2 and 2.3 (Massimo)

The tracking campaign is restarted to finalize of the study for:

• D2 field quality and update of the D2 target error table.
• study of the dependence of the dynamic aperture at injection/collision on the IP1/5 phase advance.
• assess the impact of the new expected error table for triplet quadrupoles including the change in the systematic multipoles (reduction of b₆ and increase of b₁₀ and b₁₄).
• Impact of new Q4 error table.

Task 2.4 (Elias)

A new student (C. Tambasco) will work with Tatiana and Elias on the study of the interplay between beam-beam and impedance.

Nicolo Biancacci is starting to work on impedance issues for HL-LHC

The INFN colleagues (M. Zobov and O. Frasciello) are benchmarking GdFidl with CST to further improve the model of the collimators.

Task 2.5 (Sasha & Tatiana)

Bad audio prevented Sasha to comment.

PLC (Oliver)

Oliver reported that an updated parameter table has been approved by the PLC with a change on the number of bunches and the inclusion of the RF curvature and hour-glass effect in the luminosity estimates.

Next meeting will take place regularly on Friday 4^th July 2014 at 16:00.

Reported by Gianluigi and Riccardo.