Synthetic model of gamma-ray emission during DT experiments on the SPARC tokamak

TL;DR

This paper presents a detailed simulation of gamma-ray emission in the SPARC tokamak, assessing detector placement, signal-to-noise ratios, and the potential for gamma spectroscopy to measure fusion power during high neutron yield experiments.

Contribution

It introduces a comprehensive simulation framework combining plasma profiles, radiation transport, and detector modeling for gamma-ray diagnostics in SPARC.

Findings

Gamma-ray signals can be distinguished from neutron background with optimized detector placement.

A neutron attenuator can enable gamma spectroscopy during high neutron yield operations.

LaBr3 detectors are effective in reconstructing fusion power in SPARC.

Abstract

In thermonuclear plasmas, plasma ions undergoing nuclear reactions emit gamma-rays with energies in the MeV range. Their spectroscopy can convey much plasma information, such as the DT fusion power, the spatial and velocity distributions of the fast ions, and the plasma heating performance. In the present work, we simulate the gamma-ray emission expected in the SPARC tokamak during a primary reference discharge, when the tokamak is expected to generate $140$ MW of fusion power and reach an energy gain factor of $Q\approx11$. We focus particularly T(D, $\gamma$)He-5, B-10(He-4, p $\gamma$)C-13 and D(He-3, $\gamma$)Li-5 reactions. We use realistic plasma profiles calculated with the TRANSP code and simulate radiofrequency heating of the plasma with CQL3D and TORIC. Possible locations for gamma spectrometers based on lanthanum bromide inorganic scintillators are suggested. For each, the signal-to-noise ratio of gamma-rays over neutrons is evaluated using the ray-tracing code ToFu and high fidelity Monte Carlo models (MCNP and OpenMC) to solve radiation transport in SPARC. A dedicated neutron attenuator made of high density polyethylene is scoped to allow gamma-spectroscopy during high neutron yield experiments. And finally, the performance of LaBr$_3$ detectors in reconstructing the fusion power generated by SPARC is discussed.