A. Suraci

Influence of thermal cycling on cryogenic thermometers

The stringent requirements on temperature control of the superconducting magnets for the Large Hadron Collider (LHC), impose that the cryogenic temperature sensors meet compelling demands such as long-term stability, radiation hardness, readout accuracy better than 5 mK at 1.8 K and compatibility with industrial control equipment.

The Superfluid Helium Cryogenic System for the LHC Test String: Design, Construction and First Operation

A major milestone in the preparation of the Large Hadron Collider (LHC) project is the testing and operation of a 50-m long superconducting magnet string, representing a half-cell of the machine lattice. This also corresponds to the length of the elementary cooling loops providing refrigeration at the 1.9 K, 4.5-to-20 K, and 50-to-75 K levels to the LHC cryomagnets. Based on existing large-capacity cryogenic infrastructure, we have designed, built and are operating a dedicated cryogenic system feeding the LHC Test String, with installed capacities of 120 W @ 1.8 K and 10 g/s supercritical helium at 4.5 K. The system also includes 15 kA, 1.6 kA, 500 A, 250 A and 50 A current lead pairs for powering of main and auxiliary magnet circuits, as well as a 120 kW liquid nitrogen vaporizer for controlled cooldown of the 105 kg cold mass. The system is fully instrumented, controlled by dedicated industrial PLCs connected to an industrial supervision system. We report on performance in operation, including response of the system to transients such as current ramp and discharge, as well as magnet resistive transitions.

Cryogenic operation and testing of the extended LHC Prototype Magnet String

Publisher Summary A major milestone in the validation of the basic technical choices for the Large Hadron Collider (LHC) project, as far as main accelerator systems - magnets, cryogenics and vacuum- are concerned, is the testing and operation of a full-scale superconducting magnet string, representing a half-cell of the machine lattice. After the assembly, commissioning and successful first operation of a full-scale superconducting magnet string, and as a new prototype dipole magnet is added to approach final configuration, the cryogenic system has been slightly modified to allow the verification of the performance of the superfluid helium cooling loop in counter-current two-phase flow. At the same time the control system strategies have been updated and only two quench relief valves have been installed, one at each end of the string.

A LOW HEAT INLEAK CRYOGENIC STATION FOR TESTING HTS CURRENT LEADS FOR THE LARGE HADRON COLLIDER

The LHC will be equipped with about 8000 superconducting magnets of all types. The total current to be transported into the cryogenic enclosure amounts to some 3360 kA. In order to reduce the heat load into the liquid helium, CERN intends to use High Temperature Superconducting (HTS) material for leads having current ratings up to 13 kA. The resistive part of the leads is cooled by forced flow of gaseous helium between 20 K and 300 K. The HTS part of the lead is immersed in a 4.5 K liquid helium bath, operates in self cooling conditions and is hydraulically separated from the resistive part.

Experience with the String2 Cryogenic Instrumentation and Control System

Publisher Summary This chapter reports on the experience of four years of designing, installation, commissioning and maintenance, and outlines the lessons learned for the Large Hadron Collider (LHC). String2 was a 120 m full-scale model of a regular cell of the LHC accelerator arc. It was composed of eight superconducting main magnets, fed by a separate cryogenic distribution line (QRL); an electrical feed box (DFB) which supported the superconducting current leads that powered the magnets. Bearing an intensive experimental programme, String2 was heavily instrumented. The complexity of the cryogenic instrumentation and control system was close to a full 3.3 km LHC sector. The String2 facility provided validation and additional knowledge for instruments, front-end electronics, electromagnetic compatibility, fieldbus and PLC architectures, remote electronics positionners, control algorithms, programming methodology, and SCADA. In some cases weaknesses were highlighted, triggering improvements in issues such as inter-team communication, respect of instrumentation installation procedures, and documentation production or access. It was also clear that wireless access to local area network will be essential in the LHC tunnel.

First assessment of reliability data for the LHC accelerator and detector cryogenic system components

The Large Hadron Collider (LHC) cryogenic system comprises eight independent refrigeration and distribution systems that supply the eight 3.3 km long accelerator sectors with cryogenic refrigeration power as well as four refrigeration systems for the needs of the detectors ATLAS and CMS. In order to ensure the highest possible reliability of the installations, it is important to apply a reliability centred approach for the maintenance. Even though large scale cryogenic refrigeration exists since the mid 20th century, very little third party reliability data is available today. CERN has started to collect data with its computer aided maintenance management system (CAMMS) in 2009, when the accelerator has gone into normal operation. This paper presents the reliability observations from the operation and the maintenance side, as well as statistical data collected by the means of the CAMMS system.

FIRST EXPERIENCE WITH THE LHC CRYOGENIC INSTRUMENTATION

The LHC under commissioning at CERN will be the worlds largest superconducting accelerator and therefore makes extensive use of cryogenic instruments. These instruments are installed in the tunnel and therefore have to withstand the LHC environment that imposes radiation-tolerant design and construction. Most of the instruments require individual calibration; some of them exhibit several variants as concerns measuring span; all relevant data are therefore stored in an Oracle® database. Those data are used for the various quality assurance procedures defined for installation and commissioning, as well as for generating tables used by the control system to configure automatically the input/output channels. This paper describes the commissioning of the sensors and the corresponding electronics, the first measurement results during the cool-down of one machine sector; it discusses the different encountered problems and their corresponding solutions.