Ion Temperature Inference from Neutron Counting in Maxwellian Deuterium Plasmas

TL;DR

This paper introduces a neutron counting method using liquid scintillators to infer ion temperature in Maxwellian deuterium plasmas, offering a time-resolved, non-invasive diagnostic suitable for Magnetized Target Fusion.

Contribution

The paper presents a novel neutron-based ion temperature inference technique that does not require direct plasma line-of-sight or neutron collimation, with detailed calibration and uncertainty analysis.

Findings

Successfully applied to General Fusion's PI3 device

Achieved time-resolved ion temperature measurements

Validated results against Ion Doppler spectroscopy

Abstract

A method is presented for inferring the deuterium fuel ion temperature from neutron counts measured with fast liquid scintillators in conditions where the ion velocity distribution is Maxwellian. Local neutron count rates at each scintillator position are combined to estimate total neutron yield from the plasma, where absolute detection efficiency is determined via MCNP neutron scattering simulation based on a 3D model of the experiment structure. This method is particularly advantageous for Magnetized Target Fusion applications as it yields a time-resolved diagnostic and does not require direct line-of-sight to the plasma or collimation of the neutrons. The instrumentation configuration, pulse-shape discrimination and pile-up correction algorithms, detector calibration, and ion temperature calculation method with uncertainty characterization are discussed. An application of the method to General Fusion's Plasma Injector~3 (PI3) spherical tokamak device is demonstrated and the results are compared to an Ion Doppler spectroscopy ion temperature diagnostic.