Calculations to Evaluate the Use of the Attenuation of D-D Neutrons in Liquid Oxygen as a Means of Measuring Plasma Ion Temperature

The ion temperature of a deuterium plasma with a Maxwellian distribution can be determined by measuring the transmission of the deuterium-deuterium (D-D) neutrons, i.e., neutrons produced by the reaction D + D → n + ³He, through liquid oxygen. In practice the measurement requires both collimation and shielding to ensure that the attenuation of only those neutrons emitted directly from the plasma is measured. Calculated results are presented of the collimation and shielding required to reduce the background so that the ion temperature can be measured. The geometric configuration used in the calculations is that of the Impurity Studies Experiment (ISX) at the Oak Ridge National Laboratory, but the results will provide insight into the application of the measurement method at other plasma facilities. Results are presented for D-D plasma temperatures of 2, 6, and 10 keV and for two sizes of NE-213 detectors. It is concluded that the counting rates are too low to make the measurement feasible at ISX.