The Compound Cryogenic Distribution Line for the LHC: Status and Prospects

After a pre-series phase qualifying the design of three European firms, CERN adjudicated end of 2001 one contract for the manufacturing and installation of the cryogenic distribution line (QRL) for the LHC (Large Hadron Collider). Each of the eight ~3.2 km QRL sectors is feeding helium at different temperatures and pressures to the local cooling loops of the strings of superconducting magnets operating in superfluid helium below 2 K. With an overall length of 25.8 km the QRL has a very critical cost to performance ratio. We present a project overview describing all phases, status and schedule

An Experimental Study of Cold Helium Dispersion in Air

The Large Hadron Collider (LHC) presently under construction at CERN, will contain about 100 tons of helium mostly located in the underground tunnel and in caverns. Potential failure modes of the accelerator, which may be followed by helium discharge to the tunnel, have been identified and the corresponding helium flows calculated. To verify the analytical calculations of helium dispersion in the tunnel, a dedicated test set-up has been built. It represents a section of the LHC tunnel at a scale 1:13 and is equipped with a controllable helium relief system enabling the simulation of different scenarios of the LHC cryogenic system failures. Corresponding patterns of cold helium dispersion in air have been observed and analysed with respect to oxygen deficiency hazard. We report on the test set-up and the measurement results, which have been scaled to real LHC conditions

Experimental Simulation of Helium Discharge into the LHC Tunnel

The LHC cryogenic system contains about 100 tons of liquid helium. The highest amount of helium is located in the magnet cold mass (about 58 tons @ 1.9 K, 0.13 MPa), in the QRL supply header C (about 26 tons @ 4.6 K, 0.36 MPa) and in the ring line (about 0.7 tons 290 K, 2 MPa). The rupture of header C is one of the failures leading to the worst scenario of helium discharge into the tunnel. To investigate the consequences of this failure an experiment has been performed. This paper presents the layout of the test set-up and compares the experimental results with calculated data

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

Helium Discharge and Dispersion In the LHC Accelerator Tunnel in Case of Cryogenic Failure

The Large Hadron Collider (LHC), presently under construction at CERN, will contain about 100 tonnes of helium, mostly located in the underground tunnel and caverns [1]. Potential failure modes of the accelerator, which may be followed by helium discharge to the tunnel, have been identified and the corresponding helium flows calculated. The paper presents the analysis of the helium discharge in the worst case of conditions, as well as the corresponding helium dispersion along the tunnel. The variation of oxygen concentration has been calculated and the oxygen deficiency hazard (ODH) analysed. The preventive means of protection, namely location and sizing of safety valves are also discussed

Results from the Qualification of the three Pre-series Test Cells for the LHC Cryogenic Distribution Line

Three pre-series test cells of the LHC cryogenic distribution line, manufactured by three European industrial companies, have been tested in the years 2000 and 2001 to qualify the design proposed and to verify the thermal and mechanical performances. The pre-series test cell, about 112 m long, consisted of a standard cell (about 107 m long) and an additional service module needed for test purposes. This paper summarises and compares the main results of the qualification tests to the requirements of the technical specification. Technical considerations on the measurement stability and corresponding overall error are also presented

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

CLIC RF High Power Production Testing Program

The CLIC Power Extraction and Transfer Structure (PETS) is a passive microwave device in which bunches of the drive beam interact with the impedance of the periodically loaded waveguide and generate RF power for the main linac accelerating structure. The demands on the high power production (~ 150 MW) and the needs to transport the 100 A drive beam for about 1 km without losses, makes the PETS design rather unique and the operation very challenging. In the coming year, an intense PETS testing program will be implemented. The target is to demonstrate the full performance of the PETS operation. The testing program overview and test results available to date are presented