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

Cooling with Superfluid Helium

The technical properties of helium II ('superfluid' helium) are presented in view of its applications to the cooling of superconducting devices, particularly in particle accelerators. Cooling schemes are discussed in terms of heat transfer performance and limitations. Large-capacity refrigeration techniques below 2 K are reviewed, with regard to thermodynamic cycles as well as process machinery. Examples drawn from existing or planned projects illustrate the presentation. Keywords: superfluid helium, cryogenicsComment: 24 pages, contribution to the CAS-CERN Accelerator School: Superconductivity for Accelerators, Erice, Italy, 24 April - 4 May 2013, edited by R. Baile

Numerical Analysis of the Recooling of a LHC Sector from 30 K to 1.9 K following Resistive Transition of a Magnet String

To analyze the recovery process from a resistive transition of a magnet string of a LHC sector, a mathematical model is established based on the existing models describing the cooldown from 300 K to 1.9 K. In the new model, the number of magnet strings which undergo a resistive transition, as well as their location are considered. According to the analysis, the recovery process is optimized as well as the temperature evolution in the magnet cold-mass, the pressure profile in the very low pressure header during the recool-down process and the time used for the recool-down are presented

Refined Studies of Cooldown and Warmup for the Large Hadron Collider

Compared with the previous study [1], this paper presents and improved mathematical model which takes into account the pressure evolution in the different headers of the cryogenic distribution line and the effect of the pressure drop across the valves during cooldown and warmup modes. The application of the improved model to the LHC sectors shows that the present processes of cooldown and warmup may take a longer time by about 5% than that predicted by using the previous model. Some issues found by using the latest model have also been presented and discussed

Update of a Cooldown and Warmup Study for the Large Hadron Collider

The paper presents the inventory of components and materials for LHC magnets, especially for main dipoles and quadrupoles. A mathematical model for LHC transient modes, such as cooldown and warmup of a magnet, a standard cell and the eight LHC sectors, has been developed on the basis of the up-to-date layout of the LHC machine, and validated by experimental data. The model considers the momentum and continuity equations, as well as the energy equations for helium and materials. Based on the simulation results, the heat transfer in the magnets has been studied and the transient modes optimized

Gaseous Helium storage and management in the cryogenic system for the LHC

The Large Hadron Collider (LHC) is presently under construction at CERN. Its main components are superconducting magnets which will operate in superfluid helium requiring cryogenics on a length of about 24 km around the machine ring with a total helium inventory of about 100 tonnes. As no permanent liquid helium storage is foreseen and for reasons of investment costs, only half of the total helium content can be stored in gaseous form in medium pressure vessels. During the LHC operation part of these vessels will be used as helium buffer in the case of multiple magnet quenches. This paper describes the storage, distribution and management of the helium, the layout and the connection to the surface and underground equipment of the cryogenic system