Plasma diagnostics using an injected neutral helium beam

A diagnostic for measurement of the internal magnetic field and the ion temperature is proposed which is applicable to the current generation of magnetic fusion devices. This technique involves the injection of a neutral helium beam into the plasma. The magnetic field can be determined from Zeeman spectroscopy of the neutral beam using laser-induced fluorescence or collisional excitation. Ion temperature measurements can be made from Doppler broadening of the charge exchange recombination radiation or elastic scattering of the beam particles. Details of the beam propagation through the plasma are solved numerically using a system of coupled rate equations. The diagnostic is suitable for a wide range of plasma and machine parameters. Results from computer simulations have been obtained for the S−1 spheromak and the tokamak fusion test reactor (TFTR) which show that ∼50% of a 20-keV beam can penetrate to the center of the plasma.