In the framework of the HL-LHC project, the first phases of the commissioning of the HL-LHC power converter systems of the Inner Triplet String test facility in SM18 have been successfully completed. These phases comprised the Individual System Tests (IST) and Short Circuit Tests (SCT). As a reminder, the IT String test facility aims at a full-scale integration and operational tests of the new superconducting magnet chains, from the inner triplet quadrupoles up to the first separation/recombination dipole.

This milestone of delivering the powering equipment and its infrastructure to the IT String and completing the first phases of commissioning represents a very important achievement for the SY-EPC group and HL-LHC project. Indeed, the feedback already gained will guide both the improvement of the equipment (before final procurement of series units) and the update of procedures and sequences to test and install the final deliverables in the machine during LS3.

The equipment commissioned so far comprises a set of 20 power converters of different converter families and development status from prototype to series (series units will be the ones to be ultimately used in the tunnel) together with matching Circuit Disconnector Boxes (CDB) for the circuits ≥ 2kA and Water Cooled Bus-Bars (WCBB) for the circuits ≥ 14kA.

Equipment / Rating	Status	Quantity
HL-LHC 18kA±10V	Prototype	1
HL-LHC 14kA-08V	Prototype	1
HL-LHC±2kA±10V	Pre-series	8
HL-LHC±35A-10V	Prototype	1
CDB 18kA (same for 14kA)	Series	2
CDB 2kA	Series	8
WCBB 18kA (same for 14kA	Series	2 sets
R2E-HL-LHC±200A±10V	Series	1
LHC±120A±10V	LHC Spare	8

The ISTs consisted of visual inspection, verification of connections (AC, cooling water, earthing, communication network) and services (control software, SY-EPC database, …) after connection to the infrastructure, verification of individual equipment interface with the infrastructure and, finally, verification of the interface between SY-EPC equipment.

The SCTs validated the complete powering equipment of the electrical circuits operating at room temperature including the different thermal aspects, from the 400 V AC network until the water-cooled/air-cooled cables and room temperature high current WCBBs before their connection to the superconducting elements in the circuits. In the IT String a dedicated mock-up has been designed, produced and installed to simulate the connection to the cold part made through the Current Leads (CL) of the DFHX cold box and realize the “short circuit”. All power converters have been tested at the ultimate current (equivalent to 7.5 TeV) of their respective circuits.

Innovative features have been introduced for the HL-LHC warm powering system and firstly appeared in the IT String:

• the HL-LHC18kA power converter implements energy recovery (during ramp downs) by means of Lithium Titanate Oxide batteries which also improve the immunity to the AC grid;
• the CDBs implement, in hardware, the compliance with the different electrical standards used for electrical installations (i.e. NF-C18-510 for the lockout procedure, NF-C15-100 for the rules on electrical installations and EN-60529 for the Ingress Protection for enclosures) and guarantee better and safer operation around the CLs;
• the WCBBs implement the optimal solution to link the CDBs and the CLs; they feature isolated water-cooled plate assemblies to comply with the strict requirements both in terms of power dissipated towards the CLs and in terms of maximum allowed leakage currents imposed by the ElQA tests.

Although precision qualification has not been part of the completed commissioning steps, it is worth mentioning that 18kA power converter (Inner Triplet main circuit) and 14kA power converter (separation/recombination dipoles circuits) feature unprecedented capabilities in terms of precision such as sub-ppm (parts-per-million) stability and low frequency noise and are currently equipped with pre-series DCCTs and series ADCs of accuracy Class 0. Full compliance with Class 0 requirements will be tested during the next commissioning phases with the actual superconducting magnet chains.

Figure 1 Right side: HL-LHC 18kA±10V power converter. Left Side: end part of the WCBBs connecting to the mock-up of the DFHX (Current Leads side) used to simulate the “Short Circuit” configuration.

Figure 2 Left side: R2E-HL-LHC±200A±10V power converter beside the Energy Extraction System (EES) rack. Right Side: HL-LHC±2kA±10V power converters (front side, EES racks are installed on the rear side).

Figure 3 Left side: HL-LHC 14kA-08V power converter (front side). Right Side: HL-LHC 14kA-08V power converter thermal imaging during a heat run at ultimate current (rear side).

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