Kinetic theory of a transition layer in a diamagnetic bubble at a finite electron temperature

Plasma equilibrium with a pressure close to the magnetic field pressure ( β ~ 1 ) are actively studied both in relation to various cosmic phenomena and in the context of more efficient plasma confinement in the magnetic traps. In particular, one of the most promising paths in the development of mirror traps is the transition to the diamagnetic confinement regime. In such a regime, a powerful neutral injection should create an extremely high-pressure plasma with a completely displaced magnetic field (a diamagnetic bubble) in the centre of the trap. The width of the transition layer in this bubble is an important parameter controlling the rate of longitudinal plasma losses. Previously, a model describing the structure of the transition layer in a bubble (Kotelnikov 2020 Plasma Phys. Control Fusion vol. 67, p. 075002) was built on the basis of the collisionless kinetic theory and, using the cold electron approximation, predicted the layer width at the level of ten ion gyroradii. In this paper, the model is generalised to the case of finite electron temperature, requiring us to take into account the electric potential in a self-consistent manner. It is found that, given the comparable temperatures of the ion and electron components, the plasma boundary has a two-scale structure similar to the recently discovered sub-ion magnetic holes. In the inner part of the transition layer, a noticeable jump in the magnetic field is provided exclusively by the electron current on a scale of less than ten electron gyroradii, the remaining part of the jump is created by the diamagnetic ion current on a much longer ion gyroradius scale.