Ignition in a tokamak reactor with INTOR-like parameters

The requirements for ignition in a tokamak reactor with INTOR-like parameters were studied using a one-dimensional transport code. With "empirical" electron energy diffusivity χ_e, ignition was obtained with 60-75 MW of neutral beam injection at a volume average pressure ratio 〈β〉=4-5% under a variety of conditions. Changing χ_e gave ignition at the same 〈β〉 if the plasma minor radius varied as a ∞ χ_e^1/2. The maximum impurity concentration which allows ignition was found to be comparable to that for the much simpler case of a homogeneous plasma with radiative losses only. In long pulse simulations with efficient helium pumping, the maximum toroidal field ripple which allowed ignition was 2.0% (peak-to-peak) at the plasma edge. Ignition was maintained with over 99% recycling of helium ash using 5% less than maximum ripple.