Summary notes of the LCU meeting on 24/09/2013

Present: RA, FB, RV, HB, MF, MG, JJ, GR, AS, MS, RV, DW

This was a special meeting, dedicated to two presentations.

Potential for Stochastic Cooling of Heavy Ions in the LHC -> MS (slides)

Michaela gave a presentation, which was prepared together with John Jowett and Mike Blaskiewicz from BNL for the COOL'13 workshop in Muerren in June 2013.

More details on the experience from BNL on this subject were discussed by  Mike Blaskiewicz in his ATS seminar on the 6 June at CERN.

Increasing the luminosity in heavy ion operation in the LHC would result in rather short luminosity lifetimes of the order of 2 hours. Stochastic cooling could potentially improve this. The luminosity could be kept approximately constant over 6 hours for a single high luminosity IP in Pb-Pb operation. For three IPs, burn-out would be very significant. Still, cooling can be expected to improve a also in the case of 3 high luminosity IPs the useful fill length by a factor of two. It is planned to follow further up on this, to find possible locations in the tunnel, continue detailed simulations and define the hardware challenges like the required bandwidth.

Ghislain asked if the damping could already be used at injection energy in the LHC to reduce the emittance growth by intra-beam scattering. John replied that the time spent at injection would be too short. Roderik asked about longitudinal damping in addition to transverse damping. Michaela and John said that the main goal is transverse damping to improve the luminosity lifetime. Longitudinal damping could potentially reduce the loss of particles from the bucket, but this would be rather insignificant, particularly at top energy.

Machine upgrade and experiment protection -> HB (slides)

Helmut presented a first preview of this talk prepared for the ECFA High Luminosity LHC Experiments Workshop in Aix-Les-Bains from 1-3 October.

A second preview is scheduled with the convenors of the machine-detector interface sessionin preparation of the workshop on Friday 27 September, see indico.
Helmut describes the changes planned for the interaction regions IR1 and 5 for the HL-LHC and discusses the implications for the experiments. The reduction of the central beam pipe diameters, combined with the increased TAS and TAN apertures might reduce the passive protection of the experiments. Simulations on failure scenarios have started (for crab cavities) or are planned. Massimo stresses that some arguments used to justify the statement the the "aperture is generous" are not completely correct. For instance, not all the quantities that are used for evaluationg the aperture scale with the beam emittance. Furthermore, the collimators cannot be set taking the actual value of the beam emittance, as this would generate problems in terms of impedance. Moreover, Massimo supports all studies that can make the statement about the loss of passive protection a quantitative one.
Helmut said he would mainly concentrate on the principles and leave detailed discussions like the critical review of tolerances for the aperture requirements to our internal discussions in this meeting and the HL-LHC work packages.

Note added after the meeting :  the final version of Helmuts slides as well as other information about the workshop are available from the ECFA workshop page. 

AOB 

None

Last update: 4-October-2013

MG & HB

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