A tokamak reactor must have an ignition point which is compatible with the constraints imposed by MHD stability. One important consideration in this regard is the achievable value of β. For a wide class of transport scaling laws, ignition is energetically possible only if β exceeds a specified value, denoted by βmin; βmin must be less than the upper bound on β consistent with MHD stability. For energy confinement times of the form τE ∝nTj, j<1, algebraic relationships for βmin in terms of j and the parameters of the device are obtained. These results are then applied to a typical design of a tokamak ignition experiment.
The Belt Pinch — a high-β tokamak with non-circular cross-section