3D Monte Carlo vacuum modeling of the neutral beam injection system of ITER

ITER plans to implement several heating neutral beam injection (HNB) systems, which shoot the energetic neutral beams of hydrogen or deuterium atoms into the plasma. For efficient neutralization of the accelerated hydrogen or deuterium ions, a particular gas density profile along the beamline is required in the HNB system. A novel Monte Carlo simulation code has been developed which is able to simulate not only the beamline density profile, but also the 3D density distribution inside the vacuum vessel. This paper describes the main ideas behind and the essential features of the new code and shows how the resulting density distribution depends upon the installed cryopumping system. The numbers given in this paper refer to the reference case with deuterium operation.