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Title Thermo-mechanical analysis of cryo-cooled electrode system in COMSOL
Publication Date
Discipline/Department Physics and Astronomy
University/Publisher Uppsala University
Abstract In the planned linear accelerator called Compact Linear Collider, CLIC, electrons and positrons will be accelerated to velocities near the speed of light. A limiting factor in accelerating structures are vacuum breakdowns, which are electrical discharges from a surface as a result of a large electric field being applied. In the preparatory studies for the CLIC, Uppsala University in collaboration with The European Organization for Nuclear Research, CERN, is building a DC Spark system to analyze vacuum breakdowns. This system containing large planar electrodes will be cooled down all the way down to around 4 K in order to limit the rate of wich vacuum breakdowns happen. When cooling a system like this, which consists of different components made of different materials there is the question of how the system will be affected. The objective of this project is to investigate how the cooling will affect the stability in terms of stresses and to analyze the cool down time of the system. Another goal is to make a material recommendation for a few parts based on the results. This will be done by simulating the cooling in COMSOL Multiphysics, which is a program that uses finite element analysis to solve complex problems where different branches of physics interact. The conclusion is that the system will most likely be stable as it is and there is no need to redesign it. The choice of recommended material is alumina with the reason being it should cause the least stress and the smallest gap between the electrodes when the cooling is done. There was no big difference in the cool down time between the materials. Further studies and simulations on the system is also recommended since there are many factors not taken into consideration in this study.
Subjects/Keywords accelerator; compact linear collider; clic; cern; vacuum breakdowns; breakdowns; comsol; cryo-cooled; cryogenics; cryocooler; DC spark; electrode system; Accelerator Physics and Instrumentation; Acceleratorfysik och instrumentering
Language en
Country of Publication se
Record ID oai:DiVA.org:uu-353895
Repository diva
Date Indexed 2020-01-03

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…remaining stable. 8 2.3 Cryocooler The cryocooler is the system that is used to cool down the electrode setup to cryogenic temperatures. The cryocooler used in this setup is a PT415 from cryomech[8]. The PT 415 is a cryocooler of the type…

…x22;Two-Stage Pulse Tube Cryocooler" which has two stages where cooling takes place simultaneously. One upper part which cools down to 45 K with a power of 40 W and a lower part which cools to 4.2 K with a power of 1.5 W. 2.4 Materials The…

…materials of interest in this study is copper, steel, alumina (Al2 O3 ) and aluminium nitride (AlN). The electrodes and bottom part of the cryocooler that are connected to the electrodes will be made of copper. The spacer and plates will…

…be held at a constant temperature which in our case will be the temperature that the whole object aims to be cooled down to. 12 • Heat Flux defines the thermal flux of a boundary. It is set to be the same as the cooling power of the cryocooler

…the cooling power of the cryocooler. • Free allows the boundaries to not but held fixed at a specific place, but allows the objects surfaces to move around in accordance to the physics. • Initial Values sets the displacement field and structural…

…Simulating and post-processing results Cooling problem The boundaries of the heat transfer module and identity pairs are needed to perform the simulations for the cooling problem. The cryocooler cools the setup in two stages. In reality these stages are…

…compressed from both directions against the larger cylinder parts of both electrodes. The bottom part of the cryocooler will be placed around and above the smaller top cylinder of the electrode. The measurements that are needed to analyze stresses between…

…0.0171 -0.00539 -0.0662 -0.0168 -0.0213 -0.00539 18 4.2.3 Cryocooler bottom part Figure 9: Bottom part of the cryocooler. Measurements and materials The bottom part of the cryocooler will be made of copper and all the inner and outer diameters of…