Gas Flow in the Neutralization Region of EAST Neutral Beam Injector

The gas flow in the neutralization region affects the neutralization efficiency as well as the beam transition efficiency of whole neutral beam injector, which will be applied as a high power auxiliary heating and non-inductive current driver system for the Experimental Advanced Superconducting Tokamak (EAST). The neutralization region of EAST neutral beam injector includes not only the gas cell neutralizer in traditional sense, but also part of the ion source downstream the electrode grid, the gate valve, and the transitional piping and fitting. The gas flow in this neutralization region has been modeled and researched using an adjusted Direct Simulation Monte Carlo code to understand the formation mechanism of gas target thickness, which determines the neutralization efficiency. This paper presents the steady-state, viscous and transition region flowfields, the gas density distribution and the various centerline profiles including Knudsen number, temperature, pressure and axial velocity by injected the deuterium gas from the arc chamber and neutralizer, respectively. The target thickness in the neutralization region as a function of gas inlet quantity is also given in the absence of beam for future operation of EAST neutral beam injector.