Pressure Distribution Analysis And Experiment For NBI Experimental Device Based On Monte-Carlo Method

Neutral Beam Injector (NBI) is a device which produces high energy ion beam, neutralizes it to high energy neutral beam for tokamak plasma heating. NBI heating is of the highest heating efficiency and of the clearst physics mechanism of Tokamak heating method except ohmic heating. Some large-scale fusion devices, such as PLT,TFTR,JET,NSTX, have successfully applied NBI heating technology. The International Tokamak Experimental Reactor (ITER) also has been planed to use this technique. NBI pressure distribution is one of the key factors, which affect the neutral beam transmission efficiency, especially the reionization loss of neutral beam transmission. The research of reionization loss is in accord with the result of NBI pressure distribution analysis.In this article, the HT-7 Tokamak NBI operating principles and structure features were analyzed. The physical model of NBI experimental device was built, and the mathematical model of molecular movement and collision in the main vacuum chamber and drift tube of NBI experimental device was also established based on M-C method. Program was designed with the MATLAB software and was implemented the simulating calculation of the pressure distribution. The average pressure, molecular distribution and pressure distribution three-dimensional nephogram of the main vacuum chamber and drift tube through the gas in-taking process is gained from the simulating calculation. The NBI pressure distribution experiment was carried out on HT-7 NBI experimental device. The pressures of different positions were real-time monitored through the experiment. At the same time, the pumping performance test facility for NBI cryocondensation pump was designed. Both the result of simulation and the result of experiment indicate that the required pumping speed, in the pulse gas in-taking process, of the main vacuum chamber cryocondensation pump is 4×10⁵l/s and the cryocondensation pump of drift tube is 4×10⁴l/s for maintaining the pressure of main vacuum chamber and drift tube at level of 10^-3Pa and 10^-4Pa respectively. The results of this paper has deeper guidance meaning for the research of reionization loss in neutral beam transmission.