Chapter 6A: Cold powering of the superconducting circuits

Abstract

For the HL-LHC project, a novel concept for the cold powering of superconducting magnets has been developed. It is based on a new type of superconducting lines (hereafter referred to as Superconducting (SC) Links) that have been developed to transfer the current to the new HL-LHC insertion region magnets from remote distances. Power converters and current leads will in fact be located in the new underground areas (UR) excavated for the HL-LHC (technical galleries running aside the LHC tunnel), and the SC Links will provide the electrical connection between the current leads and the magnets – the latter being located in the LHC main tunnel. Each SC Link has a length of more than 100 m and transfers a total current of up to about |120| kA.

The benefits of the remote powering of the HL-LHC magnets via SC links are several and can be summarized as follows:

• -  Access of personnel for maintenance, routine tests and specific interventions on power converters, current leads and associated cryogenic/electrical equipment can be located in areas far away from the LHC ring and therefore radiation free, in accordance with the principle of radiation protection that optimizes doses to personnel exposed to radiation by keeping them As Low As Reasonably Achievable (ALARA);

• -  Current leads and associated cryostats (in LHC called Distribution Feedboxes, DFBs) are removed from the accelerator ring, thus leaving space in the main tunnel for other equipment. In the HL-LHC Interaction Regions (IR) around P1 and P5, no space has been reserved for DFB-type cryostats with current leads, which are now located in the new UR galleries. Connection to the magnets’ bus-bar is made at 4.2 K via short connection cryostats.;

• -  The new technical galleries are areas with less restrictive access for personnel. Access to these galleries may be granted under certain conditions even during operation of the accelerator with beam, with the advantage of reduced time for interventions on the equipment which is located there.

  The HL-LHC Cold Powering work-package (WP) conceived, developed, and is producing:

• -  High Temperature Superconducting (HTS) current leads (DFLH), based on High Temperature Superconducting (HTS) REBCO technology;

• -  SC Links (DSH) based on MgB2 technology;

• -  Cryostats in the LHC main tunnel (DF) containing the Nb-Ti cables from/to the magnets and the electrical splices to the SC Links;

• -  Cryostats (DFH) in the new technical galleries containing the splices between MgB2 and the HTS;

• -  Technologies specific to the HL-LHC Cold Powering Systems, e.g. electrical splices between HTS and MgB2, MgB2 and Nb-Ti, Nb-Ti and Nb-Ti;

• -  Cryogenic and electrical instrumentation;

• -  Definition of operating parameters (cryogenic flow and related control) and protection requirements (interlocks, protection strategy and thresholds of resistive and superconducting components).

• The cold powering systems for the HL-LHC includes: a system for the Inner Triplets, one for the Matching section magnets and finally the upgrade of the DLS in order to power the Q4, Q5 and Q6.