Measurement of ion temperatures by means of Rutherford scattering of energetic neutrals above the limiting angle

A technique to measure the ion temperature in a thermonuclear plasma is proposed, based on Rutherford scattering of a beam of energetic neutral particles by the plasma ions. If the mass of the beam particles, m/sub b/, is larger than the mass of the scattering ions, m/sub p/, a sharp maximum (limiting) angle θ/sub lim/ = sin-1(m/sub p//m/sub b/) exists in case the thermal velocities of the plasma ions are neglected. When the scattering ions have thermal velocities, however, scattering of beam particles can occur through angles larger than θ/sub lim/. Measurement of the intensity of particles above the limiting angle can be used to find the temperature of the plasma ions, with a 10% accuracy and a spatial and temporal resolution of 10 cm and a few μs, respectively, provided the ion velocity distribution is Maxwellian. A feasibility study elucidates that this method can also be used to measure the temperature of a 3He minority component