Cryogenic safety aspect of the low -\beta magnet systems at the Large Hadron Collider (LHC)

The low -\beta magnet systems are located in the LHC insertion regions around the four interaction points. They are the key elements in the beams focusing/defocusing process and will allow proton collisions at a luminosity of up to 10**34/cm**2s. Large radiation dose deposited at the proximity of the beam collisions dictate stringent requirements for the design and operation of the systems. The hardware commissioning phase of the LHC was completed in the winter of 2010 and permitted to validate this system safe operation. This paper presents the analysis used to qualify and quantify the safe operation of the low -\beta magnet systems in the Large Hadron Collider (LHC) for the first years of operation.Comment: 6 pp. ICEC 23 - ICMC 2010 International Cryogenic Engineering Conference 23 - International Cryogenic Materials Conference 2010, 19-23 Jul 2010. Wroclaw, Polan

Thermal Performance of Insulating Cryogenic Pin Spacers

Following the proposal to introduce an actively cooled radiation screen (5-10 K) for the LHC machine, the design of the LHC cryostat foresees the need for spacers between the cold mass and the radiati on screen. The thermal impedance of the chosen material should be very high and the shape selected to withstrand the contact stress due to the displacements induced by the coll-down and warm-up transi ent. A cryogenic experiment dedicated to studying the thermal behaviour of several proposed spacers was performed at the cryogenics laboratory of CERN before choosing the one to be used for further i nvestigation on the LHC full-scale Cryostat Thermal Model [1] [2]. This paper describes a quantitative analysis leading to the choice of the spacer

Instrumentation status of the low-b magnet systems at the Large Hadron Collider (LHC)

The low-beta magnet systems are located in the Large Hadron Collider (LHC) insertion regions around the four interaction points. They are the key elements in the beams focusing/defocusing process allowing proton collisions at luminosity up to 10**34/cm**2s. Those systems are a contribution of the US-LHC Accelerator project. The systems are mainly composed of the quadrupole magnets (triplets), the separation dipoles and their respective electrical feed-boxes (DFBX). The low-beta magnet systems operate in an environment of extreme radiation, high gradient magnetic field and high heat load to the cryogenic system due to the beam dynamic effect. Due to the severe environment, the robustness of the diagnostics is primordial for the operation of the triplets. The hardware commissioning phase of the LHC was completed in February 2010. In the sake of a safer and more user-friendly operation, several consolidations and instrumentation modifications were implemented during this commissioning phase. This paper presents the instrumentation used to optimize the engineering process and operation of the final focusing/defocusing quadrupole magnets for the first years of operation.Comment: 6 pp. ICEC 23 - ICMC 2010 International Cryogenic Engineering Conference 23 - International Cryogenic Materials Conference 2010. 19-23 Jul 2010. Wroclaw, Polan

A pore-scale approach of two-phase flow in granular porous media

A pore-scale model is presented for simulating two-phase flow in granular materials. The solid phase is idealized as dense random packings of polydisperse spheres, generated with the discrete element method (DEM). The pore space is conceptualized as a network of pores connected by throats, which is obtained by using regular triangulation. Theoretical formulas for calculating geometrical properties and entry capillary pressure for given pores are developed by extending the Mayer and Stowe-Princen (MS-P) theory of drainage. Such relationships are employed in the network for defining as local invasion criteria, so that the drainage can be represented by the replacement of W-phase when the threshold value is reached. The events of W-phase entrapment are considered during the coupling procedures. This pore-scale model is verified by comparing simulation results with experimental data of quasi-static drainage experiments in a synthetic porous medium. The simulated Pc −Sw curve in primary drainage is in agreement with the experimental one

What is wrong in love-weber stress for unsaturated granular materials?

This paper presents the micromechanical model for unsaturated soil in pendular regime, taking into account the roughness of the grains and the interfaces that separate the different phases present in the medium. It supplements the oral presentation with more technical content. Laplace equation is solved for two grains configuration to calculate the capillary force and all the geometric properties of the meniscus connecting the grains. Many configurations are solved and the look up table method is then used during the simulations. Results for grains moving at constant suction and constant vol- ume are presented. It is also shown that the roughness has an important impact on the value of capillary force and it is evolution with the change of suction

Dynamic PID loop control

The Horizontal Test Stand (HTS) SRF Cavity and Cryomodule 1 (CM1) of eight 9-cell, 1.3GHz SRF cavities are operating at Fermilab. For the cryogenic control system, how to hold liquid level constant in the cryostat by regulation of its Joule-Thompson JT-valve is very important after cryostat cool down to 2.0 K. The 72-cell cryostat liquid level response generally takes a long time delay after regulating its JT-valve; therefore, typical PID control loop should result in some cryostat parameter oscillations. This paper presents a type of PID parameter self-optimal and Time-Delay control method used to reduce cryogenic system parameters' oscillation.Comment: 7 pp. Cryogenic Engineering Conference and International Cryogenic Materials Conference CEC-ICMC 2011, 13-17 June 2011. Spokane, Washingto

He II Heat Exchanger Test Unit for the LHC Inner Triplet

The Inner Triplet Heat Exchanger Test Unit (IT-HXTU) is a 30-m long thermal model designed at Fermilab, built in US industry, fully automated and tested at CERN as part of the US LHC program to develop the LHC Interaction Region quadrupole system. The cooling scheme of the IT-HXTU is based on heat exchange between stagnant pressurized He II in the magnet cold mass and saturated He II (two-phase) flowing in a heat exchanger located outside of and parallel to the cold mass. The purposes of this test are, among others, to validate the proposed cooling scheme and to define an optimal control strategy to be implemented in the future LHC accelerator. This paper discusses the results for the heat exchanger test runs and emphasizes the thermal and hydraulic behavior of He II for the inner triplet cooling scheme