The transient build-up of the neutral-gas blanket in a theta-pinch reactor has been investigated. A hydrodynamic fluid code was developed to account for charge-exchange, ionization and energy transport in the plasma-neutral-gas interaction region. An initially collisionless neutral gas is separated from the vacuum region by the first wall, and at time t = 0 the wall becomes transparent to these neutrals so that half of them move freely into the boundary layer where they react with a plasma whose parameters are those given in the RTPR (Reference Theta-Pinch Reactor) design after quench. Initial neutrals react with the low-density edge of the plasma, and succeeding neutrals therefore react with the edge of a cooler plasma, removing less energy from the plasma by charge exchange. Also less energetic charge-ex change neutrals hit the wall, causing less damage as time progresses. A steady-state profile is quickly established. Essentially all the energy reaching the wall arrives in the initial pulse (about 11 μs long), and this amount of energy is insufficient to cause wall damage.
The next step in the development of a negative ion beam plasma neutralizer for ITER NBI