Development of Real-time Feedback Control System for LTX-ꞵ*

This work introduces real-time feedback control capabilities to the Lithium Tokamak Experiment-Beta (LTX-ꞵ) at PPPL [1], a spherical tokamak exploring the potential of liquid lithium to enhance plasma performance. Previously lacking feedback control, LTX-ꞵ now incorporates custom-designed dual-connectivity hardware to ensure seamless integration with both real-time and offline data systems. We adopt a barebones version of the Plasma Control System (PCS) framework developed by General Atomics [2], used in devices such as DIII-D, NSTX-U, KSTAR and EAST. Our approach emphasizes modularity and system independence in PCS development. Routine availability of feedback control aims to enhance reproducibility and extend plasma discharges, important for direct comparisons under varying wall conditions and diagnostic settings. Initial control algorithms focus on plasma current and basic position control, as the significant 3D effect of eddy currents in the thick shell surrounding the tokamak on the plasma makes real-time equilibrium reconstruction non-trivial. Future developments will investigate the use of machine learning for real-time equilibrium reconstruction and address specific challenges such as systematic optimization of the discharge and diagnostics timing to maximize performance consistency.

[1] D. Elliot et. al., IEEE TPS, 48(6), 1382-1387, 2020

[2] B. Penaflor et. al., FED, 84(7-11) 1484-1487, 2009

Supported by USDOE contracts DE-AC02-09CH11466, DE-SC0024898, and DE-SC0023481