Convective influx of plasma and beams in tokamaks with an asymmetric ripple

A method of inducing a convective influx of core plasma in tokamaks using a specially structured vertically 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. Counter streaming circulating particles will drift toward the centre owing to extra inward drift from the increased gradient whenever the particles drift through the ripple. The inward drift is manifested by B-vector x ∇B-vector drift due to the increased length of the field line and to slowing down and change in q-values. The overall effect on the diffusion of banana particles is minimal. The influx is proportional to temperature and roughly to (1-ε), where ε is the inverse aspect ratio. The enhancement of the penetration of beam injection can also be achieved by injecting the beam into the axisymmetric regions tangentially in the counter streaming direction as well as by injecting the beam perpendicularly into the ripple well. (author). Letter-to-the-editor. 33 refs, 9 figs