The mechanism for toroidal momentum input to Tokamak plasmas from neutral beams

The mechanism for transferring toroidal momentum from a neutral beam to a tokamak plasma is shown to be a combination of collisional torque and j x B torque due to fast ion radial motion. For injection into trapped ion orbits. the j x B torque exactly compensates for the lack of bounce-averaged collisional momentum transfer; it appears promptly after the beams are turned on. Injection into untrapped orbits produces a torque which is initially small, and increases to its steady state value in a few slowing down times. (C) 1999 Published by Elsevier Science B.V. All rights reserved.