Core micro-instability analysis of JET hybrid and baseline discharges with carbon wall

TL;DR

This study uses gyro-kinetic simulations to analyze core micro-instability behaviors in JET hybrid and baseline plasmas with carbon walls, highlighting the stabilizing effects of fast ion pressure and flow shear on turbulence.

Contribution

It provides new insights into the stabilization mechanisms of micro-instabilities in hybrid plasmas, emphasizing the role of fast ion pressure and flow shear effects.

Findings

Hybrid plasmas exhibit strong micro-turbulence stabilization due to fast ion pressure.

Outer core turbulence is quenched by E×B flow shear in hybrid plasmas.

Fast ion pressure contributes significantly to core confinement improvements.

Abstract

The core micro-instability characteristics of hybrid and baseline plasmas in a selected set of JET plasmas with carbon wall are investigated through local linear and non-linear and global linear gyro-kinetic simulations with the GYRO code [J. Candy and E. Belli, General Atomics Report GA-A26818 (2011)]. In particular, we study the role of plasma pressure on the micro-instabilities, and scan the parameter space for the important plasma parameters responsible for the onset and stabilization of the modes under experimental conditions. We find that a good core confinement due to strong stabilization of the micro-turbulence driven transport can be expected in the hybrid plasmas due to the stabilizing effect of the fast ion pressure that is more effective at the low magnetic shear of the hybrid discharges. While parallel velocity gradient destabilization is important for the inner core, at outer radii the hybrid plasmas may benefit from a strong quench of the turbulence transport by $\mathbf{E}\times\mathbf{B}$ rotation shear.