J. Casas-Cubillos

Neutron Irradiation Tests of Calibrated Cryogenic Sensors at Low Temperatures

This paper presents the advancement of a program being carried in view of selecting the cryogenic temperature sensors to be used in the LHC accelerator. About 10,000 sensors will be installed around the 26.6 km LHC ring, and most of them will be exposed to high radiation doses during the accelerator lifetime. The following thermometric sensors : carbon resistors, thin films, and Pt, are exposed to high neutron fluences (> 1015 n/cm2) at the ISN (Grenoble, France) Cryogenic Irradiation Test Facility in which a cryostat is placed in a shielded irradiation vault where a 20 MeV deuteron beam hits a Be target resulting in a well collimated and intense neutron beam. The cryostat, the on-line acquisition system, the temperature references and the main characteristics of the irradiation facility are described. The main interest of this set-up is its ability to monitor on-line the evolution of the sensors by comparing its readout with temperature references that are in principle insensitive to the neutron radiation (i.e. Argon gas bulbs when working at about 84 K, and below 4.5 K, either helium gas bulbs or the saturation pressure of the superfluid liquid helium bath). The resistance shifts of the different sensors at liquid helium temperatures are presented.

The superfluid helium model cryoloop for the CERN Large Hadron Collider (LHC)

The high-field superconducting magnets of the CERN Large Hadron Collider (LHC) will operate in static pressurized helium II at a maximum temperature of 1.9 K, irrespective of their position around the 26.7 km circumference of the machine ring. Their static and dynamic heat loads will be transported by conduction in the pressurized helium II, to a heat exchanger tube threading its way along the magnet string, in which flowing saturated helium II absorbs the heat in quasi-isothermal conditions. Following promising results obtained with heated flow tests on two-phase helium II, a full-scale 20 m-long thermohydraulic model of a LHC cryoloop was designed, built and operated, addressing key issues such as flow stability, steady-state heat transfer, transient response to varying loads, control strategies, and influence of slope. We present the results obtained and show that they validate the basic design choices of the proposed LHC cryogenic system.

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.

Instrumentation Amplifiers and Voltage Controlled Current Sources for LHC cryogenic Instrumentation

Instrumentation amplifiers and voltage controlled current sources have been designed by using single operational amplifiers (OPA124, TLE2071 and OPA627). Their performance has been evaluated in the laboratory and under neutron radiation. On line measurements of the offset voltages, offset currents, closed loop gain, CMRR and bias currents were performed on the amplifiers. The current sources were set to a constant value and the current was monitored on-line. The radiation tolerance of commercial voltage references has also been investigated. The radiation was performed out in ITN (Portugal) research nuclear reactor. In comparison to previous experimental campaigns the gamma radiation has been reduced by a factor 15 for a given neutron dose. This is achieved thanks to a recently constructed facility for neutron beam extraction

SEU tests performed on the digital communication system for LHC cryogenic instrumentation

Abstract The future LHC particle accelerator will use a large number of cryogenic sensors and actuators, most of which are located inside the machine tunnel and therefore in a radiation environment. These elements will communicate through a fieldbus. This paper reports the irradiation study carried out on WorldFIP fieldbus communication system. A digital communication system based on WorldFIP fieldbus protocol has been implemented and single event effects and total ionizing dose radiation tests have been performed on it.

Experiments and cycling at the LHC Prototype Half-Cell

The first version of the LHC Prototype Half-Cell has been in operation since February 1995. It consists of one quadrupole and three 10-m twin aperture dipole magnets which operate at 1.9 K. One electrical circuit powers all the magnets in series. This experimental set-up has been used to observe and study phenomena which appear when the systems are assembled in one unit and therefore influence one another.

Validation and performance of the LHC cryogenic system through commissioning of the first sector

The cryogenic system [1] for the Large Hadron Collider accelerator is presently in its final phase of commissioning at nominal operating conditions. The refrigeration capacity for the LHC is produced using eight large cryogenic plants and eight 1.8 K refrigeration units installed on five cryogenic islands. Machine cryogenic equipment is installed in a 26.7-km circumference ring deep underground tunnel and are maintained at their nominal operating conditions via a distribution system consisting of transfer lines, cold interconnection boxes at each cryogenic island and a cryogenic distribution line. The functional analysis of the whole system during all operating conditions was established and validated during the first sector commissioning in order to maximize the system availability. Analysis, operating modes, main failure scenarios, results and performance of the cryogenic system are presented.

The commissioning of the LHC test string 2

String 2 is a full-size model of an LHC cell of the regular part of the arc. It is composed of six dipole magnets with their correctors, two short straight sections with their orbit and lattice corrector magnets, and a cryogenic distribution line running alongside the magnets. The commissioning of String 2 Phase 1, with one half-cell and the following quadrupole, has started in April 2001. As for String 1, the facility was built to individually validate the LHC systems and to investigate their collective behaviour during normal operation (pumpdown, cool-down and powering) as well as during exceptional conditions such as quenches. String 2 is a stepping stone towards the commissioning of the first sector (one eight of LHC) planned for 2004. It is expected to yield precious information on the infrastructures, the installation, the tooling and the procedures for the assembly, the testing and the commissioning of the individual systems, as well as the global commissioning of the technical systems. This paper describes the procedures followed for the commissioning and details the preparation for the first cool-down and for the powering.

Radiation tests on commercial instrumentation amplifiers, analog switches & DAC's

A study of several commercial instrumentation amplifiers (INA110, INA111, INA114, INA116, INA118 & INA121) under neutron and vestigial gamma radiation was done. Some parameters (Gain, input offset voltage, input bias currents) were measured on-line and bandwidth, and slew rate were determined before and after radiation. The results of the testing of some voltage references REF102 and ADR290GR and the DG412 analog switch are shown. Finally, different digital-to-analog converters were tested under radiation.