Neutron Emission Spectrometer To Measure Ion Temperature On The Fusion Demonstration Plant

TL;DR

This paper presents the design and optimization of a multilayer coaxial time-of-flight neutron spectrometer to accurately measure ion temperature during peak compression in a fusion demonstration plant, enabling rapid temperature tracking.

Contribution

The paper introduces a compact, segmented scintillator-based neutron spectrometer optimized for high neutron yields and fast time resolution in fusion plasma diagnostics.

Findings

Accurate ion temperature measurement possible with as few as 500 coincidence events.

Fast 10 μs time resolution enables tracking rapid temperature changes.

Optimized spectrometer design minimizes neutron pileup and event ambiguity.

Abstract

General Fusion is building the Fusion Demonstration Plant to demonstrate a magnetized target fusion scheme in which a deuterium plasma is heated from 200 eV to 10 keV by piston-driven compression of a liquid-lithium liner. The multilayer coaxial time-of-flight (MCTOF) neutron emission spectrometer is designed to measure the ion temperature near peak compression at which time the neutron yield will approach $10^{18}$ neutrons/s. The neutron energy distribution is expected to be Gaussian since the machine uses no neutral beam or radiofrequency heating. In this case, analysis shows that as few as 500 coincidence events should be sufficient to accurately measure the ion temperature. This enables a fast time resolution of 10 $\mu s$, which is required to track the rapid change in temperature approaching peak compression. We overcome the challenges of neutron pileup and event ambiguity with a compact design having two layers of segmented scintillators. The error in the ion temperature measurement is computed as a function of the neutron spectrometer's geometric parameters and used to optimize the design for the case of reaching 10 keV at peak compression.