Tomography on C-2W: Time-resolved 2D Plasma Reconstructions via Improved 300-channel Bolometry System

In TAE Technologies' current experimental device, C-2W (also called ”Norman’’)¹, record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (15 - 40 keV, total power up to 20 MW), expander divertors, end bias electrodes, and an active plasma control system. Tomography offers a valuable and non-invasive diagnostic of the FRC plasma, as tomographic reconstructions of the emission profile yield important information on plasma shape, density, transient MHD behavior, and power loss due to radiation and particle flux. Recently, a bolometer system on the C-2W device has undergone extensive reconfiguration and noise troubleshooting, including a significant redesign of the acquisition electronics grounding and shielding scheme. The overhauled system consists of 300 simultaneously digitized photodiode channels with unique lines of sight that intersect a toroidal plane of the FRC near the mid-plane. The photodiodes respond to a broad range of wavelengths from XUV to NIR as well as energetic particles. Using this system, time-resolved 2D tomographic reconstructions of the near-midplane FRC emission profile are performed via several different methods, including a machine learning approach utilizing de-convolutional neural networks. The reconstructions are compared to well-known FRC equilibrium models, and the global stability of the plasma is qualitatively assessed.

[1] H. Gota et al, Nucl. Fusion 59, 112009 (2019)