EFFECT OF INTERNAL MAGNETIC-STRUCTURE ON ENERGETIC ION CONFINEMENT INTOKAMAKS

For the tokamak magnetic confinement concept, theory has predicted a d istinct relationship between the plasma shape, the internal magnetic s tructure, and the presence or absence of fast ion losses in the presen ce of plasma instabilities. We have, for the first time, carried out m easurements of the magnetic safety factor profile, q(r), in plasmas un stable to a specific instability, the so-called ''fishbone'' mode. The experimental equilibria reconstructed from these data have been used to demonstrate that when the plasma is unstable to fishbones, the fast ion confinement properties depend strongly on the radius of the magne tic surface where q(r) = 1.