Active-control of mode rotation in HBT-EP using a feedback-driven biased electrode

Fast rotation of plasmas in tokamaks has been shown to stabilize resistive wall and tearing modes and improve confinement through suppression of edge turbulence. These results are important to both the fusion community and ITER in order to achieve sustained fusion. Edge biasing is one such method shown to induce plasma rotation. In this work, we extend Columbia University’s High Beta Tokamak-Extended Pulse's (HBT-EP) facility [1] and our active GPU feedback system [2] to control plasma rotation through a biased electrode located 3 to 4 cm into the plasma. An inverse relationship between probe current and mode rotation is first characterized, and a proof-of-concept feedforward and feedback active-control system is implemented. The control system shows consistent, initial success in controlling mode rotation, and future work consists of upgraded GPU hardware and a more sophisticated feedback model.

1. J.P. Levesque, et al., Phys Plasmas 22, 056102 (2015).
2. N. Rath, et al., Rev Sci Instrum 85, 045114 (2014).