Vacuum Control and Gas Handling for COMPASS Tokamak

This paper is aimed at creating a vacuum and a gas handling subsystem. The new vacuum and the gas handling subsystem was developed at IPP/Prague after the COMPASS tokamak reinstallation. It was necessary to build a system which can operate 24/7 and be fully autonomous. A firmware programmed in the C programming language controls devices connected to the vacuum and the gas handling subsystem. The firmware is programmed at dsPIC r © Microchip r © embedded at a board assembled at IST Lisbon. The vacuum and the gas handling are connected through fiber optics to a server computer and can be controlled remotely through a workstation situated at the control room. Introduction COMPASS is a small sized tokamak with a D-shape vacuum vessel. COMPASS is approximately 10 times smaller than ITER and has the same shape of the vessel which makes it ITER relevant. COMPASS, after new reinstallation in IPP/Prague [Pánek et al., 2006], needs new vacuum and gas handling control. Heavy particles and other impurities which can be emitted from the vessel radiates in the plasma and decrease a plasma energy [Wesson, 2004]. So good high vacuum, less then 5.10Pa and clean tokamak vessel wall are very important for reaching long pulses ∼ 1s in COMPASS. Baking of vessel (which is currently developing), glow discharge and long duration of the pumping (one or two weeks) are required to reach this conditions. Due to this reason, a new remote control, firmware and hardware was developed at IPP Prague with collaboration with IST/Lisbon. Firmware is a term used to denote the fixed, usually rather small, programs that internally control various electronic devices. The term “firmware” was coined by Ascher Opler in a 1967 Datamation article [Opler , 1967]. Originalty, it meant the microcode contents of a writable control store (a specialized small area of RAM memory), which defined and implemented the computer’s instruction set. Our firmware is running 24/7 and controls all devices connected to the vacuum and the gas handling subsystem. The firmware does not need any operating system and it runs immediately after power on. This makes the system very robust no crashing of operating systems or updating it. Controlling and checking status of vacuum and gas injection is done on the PC placed outside the tokamak hall isolated from the tokamak chamber with optics fibers. A graphic interface which displays actual status of all devices connected to both subsystems is programmed in the Java programming language. Hardware principles Vacuum, gas handling and baking subsystems are used for reaching sufficient vacuum for creation tokamak discharge inside the vessel. Vacuum subsystem is on (means pumping) for 2 I am mentioning baking here only for complex view what everything is needed to have good condition for tokamak discharge. This work is focused only at gas handling and vacuum subsystem 153 WDS'09 Proceedings of Contributed Papers, Part II, 153–157, 2009. ISBN 978-80-7378-102-6 © MATFYZPRESS