Measurement of plasma density using nuclear techniques

The magnitude of a fusion reaction rate in a plasma depends strongly on the relative energy of the reacting plasma ions and less strongly on the ion number density. The ratio of two reaction rates, however, is less dependent on the relative velocities while retaining the linear dependence on the relative densities of the plasma ion species. In this manner, the ratio of t(d,n)α to d(d,n) 3He fusion reactions depends only on the ratio nt/nd, so that tritium levels in a deuterium plasma can be determined from the d–t/d–d reaction ratio (nd ≂ne). Similarly, the density of 3He can be determined in a deuterium plasma from the ratio of 3He (d, p)α to d(d,n) 3He fusion reactions. Such measurements of the 3He density are of interest since they relate to the alpha ash removal problem expected on a tokamak reactor.