Collective Thomson scattering electronics for a burning plasma device.

A collective Thomson scattering (CTS) diagnostic is under development to measure the density and energy spectrum of alpha particles in a burning plasma device. The scattering source is a 1 MW, 105 GHz gyrotron, chosen to avoid both absorption and cutoff within the burning plasma. Scattered signals are collected by seven front-end receivers spanning 100-110 GHz, each positioned at a different scattering angle. A 105 GHz notch filter with >60 dB depth protects the receivers from unscattered power, while a WR-10 bandpass filter rejects 170 GHz electron cyclotron heating signals. A 96 GHz high-pass filter enables single-sideband operation, and image rejection filters allow downconversion using a 100 GHz local oscillator to an intermediate frequency range of 2-12 GHz. The seven front-end receiver modules provide >30 dB conversion gain. The back-end electronics comprise 28 radiometer modules that generate 448 frequency channels, with high-resolution (100 MHz spacing) and low-resolution (190 MHz spacing) configurations optimized for bulk ion and fast-ion measurements, respectively. Detailed sensitivity analysis, accounting for system losses, receiver noise, and expected plasma emission, predicts a signal-to-noise ratio of >10 for the bulk ion feature and >5 for the fast-ion tails under nominal operating conditions, demonstrating the diagnostic's viability. The CTS diagnostic is predicted to achieve a spatial resolution of ∼5 cm and a time resolution of 80 ms, sufficient to resolve alpha-particle slowing-down dynamics.