Transition to supersonic flows in the edge plasma

Abstract

With a proper choice of a single dimensionless control parameter one describes the transition between subsonic and supersonic flows as a bifurcation. The bifurcation point is characterized by specific properties of the control parameter: the control parameter has a vanishing derivative in space and takes the maximum possible value equal to 1. This method is then applied to the sheath plasma with constant temperatures, allowing one to recover the Bohm boundary condition as well as the location of the point where the bifurcation takes place. This analysis is extended to fronts, rarefaction waves and divertor plasmas. Two cases are found, those where departure from quasineutrality is mandatory to generate a maximum in the variation of the control parameter (sheath and fronts) and those where the physics of the quasineutral plasma can generate such a maximum (rarefaction waves and supersonic flow in divertors). The conditions that are required to recover the Bohm condition, when modelling the wall using the penalization technique, are also addressed and generalized.

Study of mirror effect on scrape‐off layer‐divertor plasma based on a generalized fluid model incorporating ion temperature anisotropy

“…The relation between ν * and the ion temperature anisotropy T i,∥ / T i,⊥ agreed well with the result of a kinetic particle simulation . Moreover, thanks to the virtual divertor (VD) model, which reproduces the effects of divertor plates and accompanying sheath regions by using artificial sinks for the plasma particle, momentum and energy just like the penalization technique, the Bohm condition was automatically satisfied, and a supersonic plasma flow in a radiative‐cooling divertor region was self‐consistently simulated.…”

Investigation of Edge and SOL Particle Flux Patterns in High Density Regimes using SOLEDGE2D‐EIRENE Code

“…Following the same strategy for www.cpp-journal.org energy boundary conditions, the heat flux are forced to the sheath transmission values: q wall = γ α k B nuT α with γ e = 4.5 for electrons and γ i = 2.5 for ions. More details on the physical basis and numerical investigations performed to validate this approach and veryfing that Bohm's boundary conditions are satisfied can be found in [1][2][3]7]. In order to take into account the impact of neutrals on plasma transport, SOLEDGE2D has been coupled to the Monte-Carlo code for neutrals EIRENE [8,9].…”

Kinetic theory of quasi-stationary collisionless axisymmetric plasmas in the presence of strong rotation phenomena

“…(30), while the functional dependences of the leading-order term K s vary for v Ãs and X Ãs according to Eqs. (29) and (30), respectively. In addition to this, we must introduce explicitly the condition of having a supersonic plasma.…”

“…(30). Given validity of these assumptions, we can preliminary evaluate separately the contribution Z s e c w Ãs X Ãs entering Eq.…”

“…The treatment of equilibrium collisionless plasmas subject to strong shear flows in the framework of kinetic theory can, therefore, represent the basis for subsequent analysis of the stability properties and turbulence mechanisms in these systems. Moreover, strong rotation phenomena are expected to arise in plasmas occurring in the solar environment [21][22][23] and they are subject of current theoretical [28][29][30] and experimental [31][32][33][34][35] studies. As far as laboratory plasmas are concerned, it is well-known that the appearance of shear-flows is ubiquitous in axisymmetric confinement devices.…”