Recent Developments and Qualification of Cryogenic Helium Flow Meters

Flow measurement of cryogenic fluids is a useful diagnostic tool not only to assess thermal performance of superconducting devices and related components but also for early diagnosis of faulty components/systems and to assure the correct sharing of cryogenic power. It is mainly performed on the recovery at room temperature of vapor from liquid boil-off due to lack of commercially available robust and precise cryogenic mass flow meters. When high-accuracy or fast-time response is needed, or individual gas recovery at room temperature is not available, it is necessary to measure directly the fluid feed at cryogenic temperature. The results of extensive testing of industrially available and in-house developed flowmeters outlining characteristics and advantages of each measuring method are presented

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. A cryogenic test station has been designed and built in order to assess the thermal and electrical performances of 13 kA prototype current leads. We report on the design, commissioning and operation of the cryogenic test station and illustrate its performance by typical test results of HTS current leads

Thermohydraulics of Resistive Transitions of the LHC Prototype Magnet String: Theoretical Modeling and Experimental Results

In preparation for the Large Hadron Collider (LHC) project, a 40 m-long prototype superconducting magnet string, representing a half-cell of the machine lattice, has been built and operated. The superconducting magnets which comprise this string normally operate in a pressurized static bath of superfluid helium at a pressure of 1 bar and at a temperature of 1.9 K. At 13.1 kA they have about 15.3 MJ of stored magnetic energy. A series of tests was performed to assess the thermohydraulics of resistive transitions (quenches) of the string of magnets. These measurements provide the necessary foundation for describing of the observed pressure rise as the combination of two processes, each acting on a different time scale. The measurements are presented and an explanatory model description of the events is given

A Facility for Accurate Heat Load and Mass Leak Measurements on Superfluid Helium Valves

The superconducting magnets of the Large Hadron Collider (LHC) will be protected by safety relief valves operating at 1.9 K in superfluid helium (HeII). A test facility was developed to precisely determine the heat load and the mass leakage of cryogenic valves with HeII at their inlet. The temperature of the valve inlet can be varied from 1.8 K to 2 K for pressures up to 3.5 bar. The valve outlet pipe temperature can be regulated between 5 K and 20 K. The heat flow is measured with high precision using a Kapitza-resistance heatmeter and is also crosschecked by a vaporization measurement. After calibration, a precision of 10 mW for heat flows up to 1.1 W has been achieved. The helium leak can be measured up to 15 mg/s with an accuracy of 0.2 mg/s. We present a detailed description of the test facility and the measurements showing its performances

Cryogenic operation and testing of the extended LHC prototype magnet string

After the assembly, commissioning and successful first operation of a full-scale superconducting magnet string, and as a new prototype dipole magnet was 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. We report on the cryogenic operation of the extended version of the string and the response of the system to transients

The LHC test string: first operational experience

CERN operates the first version of the LHC Test String which consists of one quadrupole and three 10-m twin aperture dipole magnets. An experimental programme aiming at the validation of the LHC systems started in February 1995. During this programme the string has been powered 100 times 35 of which at 12.4 kA or above. The experiments have yielded a number of results some of which, like quench recovery for cryogenics, have modified the design of subsystems of LHC. Others, like controlled helium leaks in the cold bore and quench propagation bewteen magnets, have given a better understanding on the evolution of the phenomena inside a string of superconducting magnets cooled at superfluid helium temperatures. Following the experimental programme, the string will be powered up and powered down in one hour cycles as a fatigue test of the structure thus simulating 20 years of operation of LHC