Pressure Distribution Analysis And Structural Design For Neutral Beam Injector

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. 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 Experimental Advanced Superconducting Tokamak(EAST) NBI operating principles and structural features were analyzed. The geometric and physical models of EAST NBI were built, and the mathematical model of molecular movement and collision in the main vacuum chamber of EAST NBI 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 three-dimensional schematic of molecular distribution and the curves of average pressure for three areas of the main vacuum chamber were gained. The result was verified by the experimental datum of DIII-D NBI,which indicated that :1.the result of simulating calculation was reliable and effective;2. when the position of gas baffle in the first section of main vacuum chamber reached 300mm and the position of front cryopanel in the third section was 250mm,which could maintain the suitable gradient of pressure distribution through the gas in-taking process.The structures of neutralizer,deflecting system and cryopumping system were designed,that could provide engineering guide for the building of NBI.