24th HiLumi WP2 Task Leader Meeting

6-R-018 (CERN)



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Riccardo De Maria
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Minutes of the 24th WP2 Task Leader Meeting held on 28/02/2014

Present: G. Arduini, I. Bejar Alonso, O. Brüning, R. De Maria, P. Fessia, M. Giovannozzi, R. Jones, E. Métral, T. Pieloni, S. Redaelli, H. Schmickler, A. Valishev, A. Wolski.

Minutes and Follow-up of Actions (Gianluigi)

  • The program of the vacuum technical meeting scheduled for 5/3 has been defined. Three presentations will be given from WP2 members:

    • Electron cloud simulation status (G. Rumolo)

    • Impedance considerations in the design of the beam screen (N. Mounet)

    • Aperture constraints from optics considerations (R. De Maria)

The first two presentations have already been given at the Task 2.4 meeting on Wednesday 26/2. The third one will be presented during this meeting.

  • P. Fessia has discussed with the colleagues for the aspects related to the integration of the crab cavities and he will show a couple of slides presenting the status of the integration and proposals for discussion.

  • A meeting is going to take place to discuss the status of the Beam-Beam module implementation in SIXTRACK and the next steps is going to take place on 6/3.

  • Riccardo will circulate an example of the output files generated by SIXTRACK with the information on the input parameters used for the simulation (after the meeting the example was put in http://sixtrack.web.cern.ch/SixTrack/www/sample/bbe52/fort.6).

  • The reduction of the D1 magnetic length from 6.7 to 6.3 m has been approved by PLC at the last meeting (18/02/2014).


Input required from WP2 for the Beam-Beam Long Range Compensator (BBC) – H. Schmickler

  • The Beam-Beam Long Range Compensator project will be based in 4 pillars:

    • Demonstrator to be installed before LS2;

    • Upgrade of the LHC instrumentation for the characterization of the effectiveness of the BBC;

    • Optimization of the BBC parameters for HL-LHC;

    • Integration studies (Rey Veness).

  • For the demonstrator the following contributions from ABP/WP2 are required:

    • Definition of the experiment. In particular the position and number of wires to be installed need to be defined. S. Redaelli noted that at present one could install the wire on the TCT upstream of the IP (in the beam direction) and on the TCL downstream of the IP (in the beam direction). This should be possible in IP5 where TCTH.4L5.B1 and TCL.5R5.B1 could be used to install the wire. This is not possible for IP1 where the wires should be installed in the vertical plane (because of the vertical crossing angle) and no vertical TCLs are installed (only the TCTV slot upstream of the IP is a candidate). It is very unlikely to be able to install additional collimators in the region close to the TCL in cell 4. Also note that there are no additional collimator control cables: only new powering cables are being pulled.

    • Definition of the observables;

    • Modelling and prediction of the expected evolution of the observables (lifetime, diffusion speed, halo generation could be possibly considered). Gianluigi noted that it might be difficult to simulate the halo generation;

    • Participation in the experiment and data analysis;

    • It is important to understand whether one should equip 4 wires.

  • Instrumentation upgrade:

    • halo monitor (2D if possible) by using:

      1. Synchrotron light monitor but it may not have sufficient dynamic range.

      2. Rest-gas ionization monitor;

      3. Experiment vertex distribution. Gianluigi mentioned that the luminous region data are presently published at very low rate (~0.01 Hz).


Oliver asked whether the dump can be used as single pass halo monitor. This should be investigated.

Gianluigi added that one should look also at the core evolution to study the impact on luminosity.

Stefano added that collimators could also be used to study diffusion and halo generation.

  • Optimization of BBC parameters for HL-LHC. Hermann sees that this activity should start form 2017 onwards. Gianluigi noted that this activity should start now to evaluate the expected impact of the BBC on HL-LHC performance. Sasha noted that a factor two improvement in dynamic aperture is expected for flat optics according to the simulation he has shown at the Crab Cavity workshop in December.

  • For the integration studies, one should try already to study integration to down-select some options.

  • Hermann raised the question whether a global compensation could work. Oliver replied that if the resonances of various order have to be compensated, the phase advances will over-constrain the required position.

  • Gianluigi asked a review of the simulations done so far. This is already being organized within task 2.5. Action: Tatiana and Sasha to organize a meeting to review the results of the studies conducted by T. Rijoff. Action: Tatiana, Sasha.

  • Hermann would like to trigger a detailed specification of all the new instruments as it was done for the LHC.


Aperture constraints from optics considerations – R. De Maria


Riccardo reviewed the aperture requirements from optics considering the nominal optics and the flat optics with *=30/7.5 cm in the crossing/aperture planes.

At present we can expect that all apertures exceeding 12 sigmas (based on the updated definition of the tolerances for the apertures being documented in a note) can be protected by the collimation system. A few areas in the triplet (Q2/Q3), D2 and TAN have been identified where this criterion cannot be satisfied. The main message that should be passed is that the definition of the dimensions and tolerances of the beam screen/cold bore aperture of the triplets and D2 should be defined as soon as possible and that aperture should be gained if possible in the above areas.


Updates from Task Leaders – O. Brüning, M. Giovannozzi, E. Métral, T. Pieloni, A. Valishev


Task 2.2 (Massimo)

Nothing to report.


Task 2.3 (Massimo)

Nothing to report.


Task 2.4 (Elias)

Nothing to report.


Task 2.5 (Tatiana)

Nothing to report.


Task 2.6 (Oliver)

Nothing to report.



There was no time to circulate the slides from P. Fessia concerning the status of the integration of the crab cavities. Paolo will circulate them by e-mail.



Future topics will be:

  • Status of crab cavity development and present specifications (Ph. Baudrenghien, R. Calaga)


Reported by Gianluigi and Riccardo.

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