Because of the extreme peaking of the external heating power, fusion reactions take place efficiently in the plasma core. Supershot discharges with greatly enhanced core confinement properties have been produced in TFTR and are being studied with the goal of increased alpha particle production. The spectra agree well with the neoclassical predictions for the alpha particles. Also the thermalization of the alphas are consistent with classical slowing-down. Preliminary radial profiles of the alpha distribution is near expectations.
Sawteeth have a large influence on the alpha distribution.
In the outer plasma regions, the trapped alpha confinement is determined by the stochastic ripple diffusion. Post NBI sawtooth oscillations effectively transport fast trapped alphas radially outwards to the stochastic diffusion domain. This transport can lead to enhanced first orbit and ripple alpha losses. This instability is only observed when the alpha distribution function is sufficiently narrow and this criterion is relaxed when the local Alfven speed is lowered. However, the alpha loss to the 20o detector has some features in common with the expected TF ripple.