Commissioning of the LHC Magnet Powering System in 2009

On 19th September 2008 the Large Hadron Collider (LHC) experienced a serious incident, caused by a defective 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) and 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 was carefully studied, then performed taking into account the history of each of the eight LHC sectors (either warmed-up or left at floating temperature). Moreover, a campaign of measurements of the bus-bar splice resistances as well as the ones internal to the cold masses was carried out with the original and 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