Collective effects, such as instabilities driven by fast fusion products and alpha-particles, in the burning plasma experiments are the most critical physics issues for the sustainment of the plasma parameters close to the ignition and for the heat fluxes to the first wall of the reactor.
Collective effects are known to result in energetic particle transport and losses in the present-day experiments. However, as it will be shown, some parameters of the burning plasmas cannot be reproduced in present devices. There are specific physical issues that only arise at dimensionless parameters relevant to next step burning plasma experiments. In addition alpha particles will have close-to-isotropic distribution function, which distinguish burning plasma experiments from present day experiments. This affects the drive for known instabilities in the plasma, such as Alfven eigenmodes, energetic particle modes, fishbones, and MHD macro-modes. Another important issue to be considered is the interaction of alphas with multiple Alfven instabilities, which are difficult to produce in present-day experiments. Even with continued progress in present-day experiments, extrapolation to burning plasma conditions will remain uncertain without burning plasma experimentation.