Abstract
After the successful Run 1 (2010-2012), the LHC entered its first Long Shutdown period (LS1, 2013-2014). During LS1 the LHC cryogenic system went under a complete maintenance and consolidation program. The LHC resumed operation in 2015 with an increased beam energy from 4 TeV to 6.5 TeV. Prior to the new physics Run 2 (2015-2018), the LHC was progressively cooled down from ambient to the 1.9 K operation temperature. The LHC has resumed operation with beams in April 2015. Operational margins on the cryogenic capacity were reduced compared to Run 1, mainly due to the observed higher than expected electron-cloud heat load coming from increased beam energy and intensity. Maintaining and improving the cryogenic availability level required the implementation of a series of actions in order to deal with the observed heat loads. This paper describes the results from the process optimization and update of the control system, thus allowing the adjustment of the non-isothermal heat load at 4.5 – 20 K and the optimized dynamic behaviour of the cryogenic system versus the electron-cloud thermal load. Effects from the new regulation settings applied for operation on the electrical distribution feed-boxes and inner triplets will be discussed. The efficiency of the preventive and corrective maintenance, as well as the benefits and issues of the present cryogenic system configuration for Run 2 operational scenario will be described. Finally, the overall availability results and helium management of the LHC cryogenic system during the 2015-2016 operational period will be presented.
Highlights
Run 1 operation period from 2009 to 2013 was unique occasion for LHC cryogenics to learn from operation at lower than designed beam energies – initially at 3.5 TeV/beam, at 4 TeV/beam
This paper describes the results from the process optimization and update of the control system, allowing the adjustment of the non-isothermal heat load at 4.5 – 20 K and the optimized dynamic behaviour of the cryogenic system versus the electroncloud thermal load
Increased beam energy and intensity as well as modified beam injection scheme reduced significantly the operational margins of the cryogenic capacity compared to previous run, and required to optimize the process and re-think the overall cryogenic system operational configuration, to cope with the increased thermal load on the beam screen circuit
Summary
Run 1 operation period from 2009 to 2013 was unique occasion for LHC cryogenics to learn from operation at lower than designed beam energies – initially at 3.5 TeV/beam, at 4 TeV/beam. Increased beam energy and intensity as well as modified beam injection scheme reduced significantly the operational margins of the cryogenic capacity compared to previous run, and required to optimize the process and re-think the overall cryogenic system operational configuration, to cope with the increased thermal load on the beam screen circuit. 2. Process optimization and update of the control system Increased beam-screen heat loads originated from the Run 2 period beams required careful management of the cryogenic cooling capacity in order to maintain the overall system availability. As the beam induced heat load is deposited on the 1.9 K superfluid helium circuit and on the 4.5 – 20 K beam screen circuit, prerequisites to Run 2 cryogenic operation with these increased beam parameters were to check thermal loads both on magnet cold masses and beam screens [3], before verifying refrigerators which were considered to have the lowest capacity margins [4]
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