Control of Resistive Wall Modes in the Spherical Tokamak

Control of Resistive Wall Modes in the Spherical Tokamak

Control of Resistive Wall Modes in the Spherical Tokamak 150 150 UKAEA Opendata
UKAEA-STEP-PR(23)01

Control of Resistive Wall Modes in the Spherical Tokamak

In this work, the MARS-F/K codes (Liu Y Q et al 2000 Phys. Plasmas 7 3681 & Liu Y Q et al 2008 Phys. Plasmas 15 112503) are utilized to model the passive and active control of the n=1 (n is the toroidal mode number) resistive wall mode (RWM) in a spherical tokamak (aspect ratio A=1.66). It is found that passive stabilization of the RWM gives a relatively small increase in normalized beta above the no-wall limit, relying on toroidal plasma flow and drift kinetic resonance damping from both thermal and energetic particles. Results of active control show that with the flux-to-voltage control scheme, which is the basic choice, a proportional controller alone does not yield complete stabilization of the mode. Adding a modest derivative action, and assuming an ideal situation without any noise in the closed-loop, the RWM can be fully stabilized with the plasma flow at 5% of the Alfven speed. In the presence of sensor signal noise, success rates exceeding 90% are achieved, and generally increase with the proportional feedback gain. On the other hand, the required control coil voltage also increases with feedback gain and with the sensor signal noise.

Collection:
Journals
Journal:
Nuclear Fusion
Publisher:
IOP (Institute of Physics)
Published date:
06/01/2023