MAGNET

Operation of the magnet has gone quite smoothly during the first half of this year. The magnet has been at 4.5K for the full period since January.

There was an unplanned short stop due to the CERN-wide power outage on May 28th, which caused a slow dump of the magnet. Since this occurred just before a planned technical stop of the LHC, during which access in the experimental cavern was authorized, it was decided to leave the magnet OFF until 2nd June, when magnet was ramped up again to 3.8T.

The magnet system experienced a fault also resulting in a slow dump on April 14th. This was triggered by a thermostat on a filter choke in the 20kA DC power converter. The threshold of this thermostat is 65°C. However, no variation in the water-cooling flow rate or temperature was observed. Vibration may have been the root cause of the fault. All the thermostats have been checked, together with the cables, connectors and the read out card. The tightening of the inductance fixations has also been checked. More temperature sensors have been added, to help the diagnosis if such an event occurred again. Following a series of tests at low current, under the supervision of the power converter experts from CERN/TE-EPC, it was agreed to put the converter back to full power. A thermal camera was used to confirm that the temperatures of all components were within the nominal range. Some vibration of a polycarbonate plastic protection was observed and corrected. The magnet was ramped back up to 3.8T on April 15th.

The magnet current is very stable, with no degradation, with 18164A +/-0.02A at the nominal field of 3.8T.

A minor problem occurred with the cryogenics, due to a filter on the water-cooling circuit used to cool down both the diffusion pump of the cold box and the turbines. The cooling flow was nevertheless still within the operating range. The filter was cleaned during the technical stop at the end of April when the magnet was OFF.

by Benoit Curé