Pfc / Ja - 86 - 29 Convective Influx of Plasma and Beams In

A method of inducing a convective influx of core plasma in tokamaks utilizing a specially structured vertical asymmetric ripple is proposed. In the ripple well the radial gradient of the toroidal field is increased on the flux surfaces in the plasma boundary layer below midplane. Also, the magnitude of the ripple decreases exponentially from the boundary toward the magnetic axis and is practically negligible above midplane. The guiding center orbit study demonstrates that counter-streaming circulating particles will drift toward the center due to extra inward drift from the increased gradient whenever the particle drifts through the ripple. The inward drift is manifested by B x VB drift due to the increased length of the field line, and to slowing down and change of q values. Ripple trapped particles drift upward and become circulating or banana particles. The overall effect on the diffusion of banana particles is minimal. The influx is proportional to temperature and roughly to (1 e), where e is the inverse aspect ratio. Due to this fact the enhancement of the penetration of beam injection can also be achieved by injecting the beam in the axisymmetric regions tangentially in the counter-streaming direction as well as injecting the beam perpendicularly into the ripple well.