A Nodal Model for Tokamak Burning Plasma Space-Time Dynamics

Fusion alpha heating introduces new phenomena into plasma dynamics and control. On the worrisome side is the well-known fact that the dependence of the predominantly central fusion heating mechanism, coupled with the less appreciated fact of the predominantly plasma edge location of bremsstrahlung and impurity line and recombination radiation cooling and of ion orbit loss cooling, suggests the possibility of a thermal runaway fusion power excursion in the plasma core. On the encouraging side is the fact that the fusion alpha energy is transferred first to heat the core electrons and produce electron cyclotron radiation that is transferred instantaneously, predominantly to outer plasma regions and the surrounding material wall, reducing its availability for further heating of core plasma ions. This paper discusses the temporal and spatial dependence of the various heating and cooling mechanisms involved in the burn dynamics of a fusion plasma, introduces a spatially coarse nodal space-time calculation model (suitable for dynamics and controller calculations) for the analysis of burning plasmas, and identifies the research needed to fully evaluate the parameters of such a model.