  In the years 2009-2013 the Large Hadron Collider (LHC) has been operated with
the top beam energies of 3.5 TeV and 4 TeV per proton (from 2012) instead of
the nominal 7 TeV. The currents in the superconducting magnets were reduced
accordingly. To date only seventeen beam-induced quenches have occurred; eight
of them during specially designed quench tests, the others during injection.
There has not been a single beam- induced quench during normal collider
operation with stored beam. The conditions, however, are expected to become
much more challenging after the long LHC shutdown. The magnets will be
operating at near nominal currents, and in the presence of high energy and high
intensity beams with a stored energy of up to 362 MJ per beam. In this paper we
summarize our efforts to understand the quench levels of LHC superconducting
magnets. We describe beam-loss events and dedicated experiments with beam, as
well as the simulation methods used to reproduce the observable signals. The
simulated energy deposition in the coils is compared to the quench levels
predicted by electro-thermal models, thus allowing to validate and improve the
models which are used to set beam-dump thresholds on beam-loss monitors for Run
2.
