CERN, Geneva
On 19th September 2008 the Large Hadron Collider (LHC) experienced a serious incident, caused by a bad electrical joint, which stopped beam operation just a few days after its beginning. During the following 14 months the damage was repaired, additional protection systems were installed and the measures to avoid a similar incident were taken (i.e. new layer of the Magnet Quench Protection System [nQPS], more efficient He release valves). As a consequence, a large number of powering tests had to be repeated or carried out for the first time. The re-commissioning of the already existing systems as well as the commissioning of the new ones has been carefully studied, then performed taking into account the history of each of the eight LHC sectors (warm-up, left at floating temperature,'). Moreover, a campaign of measurements of the bus-bar splice resistances has been carried out with the nQPS in order to spot out non conformities, thus assessing the risk of the LHC operation for the initial energy level. This paper discusses how the guidelines for the LHC 2009 re-commissioning were defined, providing a general principle to be used for the future re-commissioning.
CERN, Geneva
Nominal beam parameters at 7TeV/c will only be reached after some years of operation, with each proton beam having a stored energy of 360MJ. However, a small fraction of this energy is sufficient to damage accelerator equipment or experiments in case of uncontrolled beam loss. The correct functioning of the machine protection systems is vital during the different operational phases already for initial operation. When operating the complex magnet system, with and without beam, safe operation relies on the protection and interlock systems for the superconducting circuits. For safe injection and transfer of beam from SPS to LHC, transfer line parameters are monitored, beam absorbers must be in the correct position and the LHC must be ready to accept beam. At the end of a fill and in case of failures beams must be properly extracted onto the dump blocks, for some failures within less than few hundred microseconds. Safe operation requires many systems: beam dumping system, beam interlocks, beam instrumentation, equipment monitoring, collimators and absorbers, etc. We describe the commissioning of the LHC machine protection system and the experience during the initial operation.
