LHC Report: Restart preparations continue

Maintenance and consolidation work has been progressing well in both the machine and the experiments in preparation for the March restart.

A sample material is attached to the LHC (the white bag taped to the green line), to measure the radiation doses.

Additional work was required around Point 5 due to the discovery and repair of a problem with the RF fingers at the connection of two beam vacuum chambers in CMS. The repair has been completed successfully and the sector is now under vacuum. In order to avoid rushing the delicate final operations required for closing the detector, the restart of the machine has been postponed by one week, from 7 March to 14 March.

In the machine, the first cool-down to 1.9 K has started in several sectors ,and the cool-down of the whole machine is still planned to be finished by 21 February. The time window between 22 February and 14 March will be dedicated to powering and cryogenic tests.

Since 12 December, the Radiation Protection (RP) group has been deeply involved in the work in the accelerator complex to ensure the protection of people against ionising radiation. For this purpose, the RP group determines the hazards associated with prompt and residual radiation exposure and performs the radiological area classification, materials classification and risk analysis of work places.

“The radiation dose to carbon-based materials (cable and magnet coil insulation) used in the accelerator complex is recorded. Since last year, the LHC has been equipped with 550 radio-photoluminescent (RPL) dosimeters,” explains Julia Trummer from the Radiation Protection group. “RPL dosimeters are tiny glass cylinders of 6mm in length and 1mm in diameter. Radiation creates luminescence and colour centres in the glass. The luminescence centres are excited by a UV source and the intensity of the emitted light is related to the radiation dose. The doses that can be measured range from a few Gy up to MGy.”

“In order to prepare for future interventions – especially those during the next long shutdown – material samples are being placed in selected areas,” adds Cristina Adorisio, also an RP group member. “These samples contain materials used in the connections between the magnets. An activation measurement of these samples will help to estimate dose values to workers.”

by Katy Foraz for the LHC team and Julia Trummer for the RP Group