Heat loads and cryogenics for HE-LHC

We report preliminary considerations on cryogenics for a higher-energy LHC ("HE-LHC") with about 16.5 TeV beam energy and 20-T dipole magnets. In particular we sketch the heat loads scaled on the proposed principal beam parameters and size the cryogenic plants for different operating temperature of the beam screens.Comment: 4 pages, contribution to the EuCARD-AccNet-EuroLumi Workshop: The High-Energy Large Hadron Collider, Malta, 14 -- 16 Oct 201

Large Cryogenics Systems at 1.8 K

Cryogenics is now widely present in large accelerator projects using applied superconductivity. Economical considerations permanently require an increase of the performance of superconducting devices. One way to do this consists to lower their operating temperature and to cool them with superfluid helium. For this purpose, large cryogenic systems at 1.8 K producing refrigeration capacity in the kW range have to be developed and implemented. These cryogenic systems require large pumping capacity at very low pressure based on integral cold compression or mixed cold-warm compression. This paper describes and compares the different cooling methods with saturated or pressurised superfluid helium, gives the present status of the available process machinery with their practical performance, and reviews the different thermodynamical cycles for producing refrigeration below 2 K, with emphasis on their operational compliance

Helium II calorimetry for the detection of abnormal resistive zones in LHC sectors

Following the incident on a LHC sector due to an electrical arc on the main dipole bus-bar circuit, postmortem analysis of previous current plateaus has shown abnormal temperature drift in the helium II baths of some magnets in the concerned area. In order to identify other possible risky areas, a detection system based on calorimety using available precision cryogenic thermometers has been first validated by applying calibrated heating in the magnet cold-mass and then implemented in the different sectors. On the 3-km long continuous helium II cryostat of each LHC sector, this method allows detecting abnormal dissipation in the W-range, i.e. additional resistive heating due to abnormal resistance of about 40 nΩ at 7 kA and less than 15 nΩ at the nominal current of 12 kA. The paper describes the principle and the methodology of this calorimetric method and gives the results obtained on the LHC sectors

Cryogenics at CERN

The use of cryogenics at CERN was originated (in the 1960s) by High Energy Physics detectors requiring low temperature technologies to achieve the desired performance and indicates a sustained trend during the entire evolution of the CERN experimental program. More recently (in the 1980s) the need of cryogenics for CERN accelerators has shown an impressive increase due to the development of superconducting accelerating cavities and high field bending magnets. Today, the two largest detectors (ATLAS and CMS) of the LHC accelerator ask for a considerable variety of cryogenic equipments and the 27 km LHC magnets ring requires the largest 1.8 K helium refrigeration and distribution systems in the world. The status of CERN cryogenics is briefly reviewed including those systems not related to the LHC complex

1.9 K Heat Inleak and Resistive Heating Measurements on LHC Cryomagnets

The superconducting magnets of the Large Hadron Collider (LHC) distributed over eight sectors of 3.3-km long are cooled at 1.9 K in pressurized superfluid helium. During the commissioning campaign of the sectors in 2008, cold standby periods at nominal operating temperature have allowed to measure the overall static heat inleaks reaching the magnet cold masses at 1.9 K by enthalpy balance in steady-state operation. In addition, during electrical powering of the different magnet circuits, helium II calorimetry based on precision thermometry has been implemented to assess with an accuracy of 100 mW/m the additional heat loads due to resistive heating and to detect possible abnormal heat dissipation during powering. This paper describes the method applied to perform these measurements, compares the results with the expected specified values and discusses the impact of the measured values on cryo-plant tuning and operational margins

Investigation of Thermal and Vacuum Transients on the LHC Prototype Magnet String

The prototype magnet string, described in a companion paper, is a full-scale working model of a 50-m length of the future Large Hadron Collider (LHC), CERN's new accelerator project, which will use high-field superconducting magnets operating below 2 K in superfluid helium. As such, it provides an excellent test bed for practising standard operating modes of LHC insulation vacuum and cryogenics, as well as for experimentally assessing accidental behaviour and failure modes, and thus verifying design calculations. We present experimental investigation of insulation vacuum pumpdown, magnet forced-flow cooldown and warmup, and evolution of residual vacuum pressures and temperatures in natural warmup, as well as catastrophic loss of insulation vacuum. In all these transient modes, experimental results are compared with simulated behaviour, using a non-linear, one-dimensional thermal model of the magnet string

A Possible 1.8 K Refrigeration Cycle for the Large Hadron Collider

The Large Hadron Collider (LHC) under construction at the European Laboratory for Particle Physics, CERN, will make use of superconducting magnets operating below 2.0 K. This requires, for each of the eight future cryogenic installations, an isothermal cooling capacity of up to 2.4 kW obtained by vaporisation of helium II at 1.6 kPa and 1.8 K. The process design for this cooling duty has to satisfy several demands. It has to be adapted to four already existing as well as to four new refrigerators. It must cover a dynamic range of one to three, and it must to allow continuous pump-down from 4.5 K to 1.8 K. A possible solution, as presented in this paper, includes a combination of cold centrifugal and warm volumetric compressors. It is characterised by a low thermal load on the refrigerator, and a large range of adaptability to different operation modes. The expected power factor for 1.8 K cooling is given, and the proposed control strategy is explained

Cooldown of the First Sector of the Large Hadron Collider: Comparison between Mathematical Model and Measurements

The first 3.3-km long LHC sector (sector 7-8) was cooled down for the first time from room temperature to below 2.0 K from January to March, 2007. In this paper, the measured cool-down evolution of the sector is presented and compared with the calculated results. The discrepancies between the measured and calculated data are analyzed. In addition, two unexpected phenomena, unbalanced cool-down between two neighboring cells supplied by one valve, and longer cool-down time with respect to the predicted generic cool-down are thoroughly and numerically analyzed