LHC Sector Test meeting held on 23-03-2004 

Subject: Quench tests during Sector Test

Present:  Roger Bailey, Mike Lamont, Jan Uythoven, Brennan Goddard, Bernd Dehning, Rudiger Schmidt, Oliver Bruning, Jean-Pierre Kouchouck, Rhodri Jones, Barbara Holzer, Ralph Assmann

Apologies: Bernard Jeanneret. K-H Mess.

Summary:

Mike briefly summarised LHC project note 44 which has, more-or-less, been taken as defining the expected quench levels. [pdf]

Bernd then motivated the desire to perform beam induced quenches during the sector test. [pdf]

There followed a lengthy discussion. The essential conclusion was that quenches with beam should be performed. Knowledge of the quench levels and associated signals in the BLMs will be crucial for LHC operations and the sooner we can get a handle on these, the better. Key points noted:

• Rudiger mentioned the possibility of injecting into sectors 8-6 in the commissioning year before the complete machine is available. Implications of this would have to be gone into in depth.
• Check installation of IR7 against slipping scheduled date for test.
• Ralph suggests setting arc to 7 TeV and then inducing a quench to check effect of current level.
• Open questions: how many quenches? Bernd argued for around 10 to get some statistics. Quadrupole or dipoles? Simulations up to now have concentrated on dipoles, are the quads in fact more likely to experience higher beam loss and therefore be more likely to quench?

Simulations

• Need simulations of fluence and associated energy deposition in the coils,  quench levels, and damage levels.
• The sector test necessarily implies a rapid loss of beam. In this limited case, it is assumed that the heat deposited has no time diffuse. Rudiger noted that A. Seimko had performed simulations with direct heating.
• It's clear that the numbers quoted in LHC project report 44 should be revised for critical locations, with the margins quoted there very much open to debate.
• It was also noted that subsequent simulations had been performed with a perfect machine with linear tracking and without the complete aperture model, implying the assumption of similar proton loss for all magnets.
• Alignment and orbit should be included in future simulations.
• Aperture "holes" exist e.g. near the quadrupoles in the arcs... could make localised losses even more localised. Some questions as to why this might be so.
•  process. Apparently there have been a variety of attempts by various teams at CERN. Need to coordinate this effort. Rudiger will follow up.

Possible experiments

• SPS discussed as possible test bed. Different geometry, material in front of BLMs, usefulness questioned. 
• JPK suggests extraction from SPS into dedicated superconducting magnets. This possibility should be investigated further. Potential cost of cryogenic infrastructure a possible limitation.
• Usefulness of experience at other labs debated. DESY were off by two orders of magnitude in their loss versus quench level predictions apparently. Experiments at RHIC or DESY?