Influence of ion-neutral collisions on the impact of edge biasing in a tokamak plasma

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Abstract
The effect of ion-neutral collisions on the dynamics of potential edge biasing in a tokamak plasma is studied. Under the influence of such collisions the ions and electrons drift differently thereby creating a non-ambipolar mechanism that impacts the radial electric field created by the biasing. This is similar to the effect of electron and ion mobilities that has been investigated in the past (Shankar et al 2024 Nucl. Fusion 64 076041). In this work, we carry out a consolidated investigation of the edge biasing dynamics in the presence of both ion-neutral collisions and electron/ion mobility contributions. Our detailed numerical simulations of an extended set of model equations reveal that both these contributions permit a different level of turbulence to exist. However, the extent of their individual impacts and influence on the spectral characteristics of the turbulence differ as a function of the plasma parameters. We present a detailed analysis of the physical origin of the stabilizing contribution due to ion-neutral collisions, followed by a comparison with similar effects arising from electron/ion mobility contributions. The practical implications of our findings for edge control in low-temperature tokamaks are discussed.

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