Dynamic response of detached plasma to intermittent heat and particle fluxes induced by double-pulse ECH in GAMMA 10/PDX

Detached plasma dynamics under transient upstream perturbations were investigated in the divertor simulation module of GAMMA 10/PDX using double pulse central electron cyclotron heating (C ECH) to generate controlled transient heat and particle fluxes. Detached plasma was produced by radiator gas injection, and its temporal evolution was measured with electrostatic probes, Thomson scattering, microwave interferometry, and high speed Balmer line imaging. The intermittent particle fluxes generated by C ECH induced rapid and repeatable transitions between detached and attached states, with characteristic collapse and recovery times of approximately 1 ms. Spatiotemporal H alfa/H beta measurements revealed a transient, heating-driven shift of the recombining (MAR-dominated) region toward the target plate, accompanied by a transition to an ionization-dominated regime. Comparison with a collisional–radiative model indicates that the observed variations in H alfa/H beta reflect temperature driven changes in excitation and recombination processes, although the line integrated nature of the measurement limits quantitative comparison. The response times are comparable to those reported in Magnum PSI transient pulse experiments, demonstrating that detachment stability is sensitive to millisecond scale perturbations across different magnetic configurations and plasma species. These results establish double pulse C ECH as a precise actuator for studying and controlling detachment like plasma states in the end region of mirror devices.