http://indico.cern.ch/getFile.py/access?sessionId=8&resId=1&materialId=1&confId=164089

That info contains a lot of jargon and mystery for us lay people - luminosity, beam dump, quench, scrubbing, pile up, etc* - but here are a few points of interest:

- LHC is designed for a maximum power of 14TeV, i.e. 7TeV/beam.
- Thus far, it's been using only 3.5TeV/beam, as this was least likely to cause 'risk associated with quenches', and was considered probably sufficient for immediate purposes inc. the search for the Higgs boson.
- It's been decided to increase to 4TeV. With upgrades during the past year, it's calculated that the risk at 4TeV will now be =< the risk at 3.5TeV last year.

"Beam Energy after LS1 (1st September 2014):
• Strong recommendation
• DO NOT GO FOR 7TeV PER BEAM DUE TO THE RISK ASSOCIATED WITH MANY HUNDREDS (THOUSAND) QUENCHES
• Around 6.5TeV/beam is safer and sufficient"

* If anyone can cast some light on the meaning of 'luminosity' (!) and so forth, I'd be glad.

LHC luminosity is basically the number of particles in the beam cross section area per unit of time.

http://www.lhc-closer.es/php/index.php?i=1&s=4&p=9&e=0

Essentially the higher the luminosity the more likely you are to get collissions as the two beam meet headon.

Thanks for the info and the useful link.

That's luminosity sorted, but what about quenches?

Sounds like it might be where the whole thing goes "phutt", or where someone has to throw water over it, but I bet there's a more technical explanation.