Kinetic Ballooning Mode Under Steep Gradient: High Order Eigenstates and Mode Structure Parity Transition

TL;DR

This paper demonstrates the existence of high order eigenstates of kinetic ballooning modes in tokamak plasmas with steep gradients, revealing intrinsic mode parity transitions and their implications for edge plasma physics.

Contribution

It introduces the concept of high order eigenstates of KBM, showing their coexistence with the ground state and their distinct mode structures and driving mechanisms.

Findings

High order KBM eigenstates coexist with the ground state.

Mode parity transition is an intrinsic property of electromagnetic plasmas.

High order KBMs can be driven by pressure gradient without collisions.

Abstract

The existence of kinetic ballooning mode (KBM) high order (non-ground) eigenstates for tokamak plasmas with steep gradient is demonstrated via gyrokinetic electromagnetic eigenvalue solutions, which reveals that eigenmode parity transition is an intrinsic property of electromagnetic plasmas. The eigenstates with quantum number $l=0$ for ground state and $l=1,2,3\ldots$ for non-ground states are found to coexist and the most unstable one can be the high order states ($l\neq0$). The conventional KBM is the $l=0$ state. It is shown that the $l=1$ KBM has the same mode structure parity as the micro-tearing mode (MTM). In contrast to the MTM, the $l=1$ KBM can be driven by pressure gradient even without collisions and electron temperature gradient. The relevance between various eigenstates of KBM under steep gradient and edge plasma physics is discussed.