Exploration of Mode Frequency Control and Observation of Multiple Independent Modes on HBT-EP

This poster explores internal mode structures with a poloidal array of 64 Extreme Ultraviolet (EUV) diodes (15 ≤ E_γ ≲ 10⁴ eV) on the HBT-EP tokamak. A combined-diagnostic Singular Value Decomposition is used to identify coherent signatures across optical and magnetic signals. One application of this study is the identification and frequency control of an internal emissive 2/1 mode structure locked to an edge magnetic 3/1 mode structure. A non-iterative tomographic scheme and projection matrix is employed to extract the phase of this feature, on an NVIDIA GPU in an 8μs cycle. HBT-EP’s 4×10 poloidal and toroidal control coils are actuated with a pre-defined surface ψ_3/1 to control the rotation frequency. Compared to phase tracking with Mirnov probes, similar ∆f_mhd of roughly ±30% is observed. A second application is the observation of multiple independent modes. The combined diagnostics show 2D profiles associated with the progression of a sawtooth event: an internal 1/1-like mode precedes the β-collapse, which in turn destabilize an edge mode. Separately, a high frequency 3/2 mode is observed independent of the dominant 3/1 mode. The correlation in time of these mode amplitudes is discussed.