A classical problem of plasma physics is the treatment of the plasma-wall transition. This can be reached in the presheath with a presheath scale, in the sheath with a sheath scale and between ...presheath and sheath with an “intermediate scale”. Riemann (J Tech Phys 41:89–121, 2000) published a derivation of the intermediate scale. In our calculation we take the non-quasineutral values for the ion density and the ion velocity at the point where the non-quasineutral solution of the potential is zero. This approach is consistent and valid also for small but finite values of the smallness parameter of the theory. An effect of taking the non-quasineutral values is that the potential is shifted, dependent on the magnitude of the smallness parameter. But this shifting has no consequences on the intermediate scale and so we get a similar result as K.-U. Riemann. Furthermore, we show that it is not necessary to take into account the temperature change in the vicinity of the sheath edge and that it is possible to work always strictly with the complete and normalized basic equations of the problem and not only with orders on the left or right hand side of these equations.
The magnetized plasma–wall transition (PWT) region typically exhibits three characteristic subregions: the “Debye sheath”, the “magnetic presheath”, and the “collisional presheath”. The fluid ...boundary conditions for transport codes (simulating, e.g., the scrape-off layer (SOL) of a tokamak) are usually applied at the “magnetic presheath entrance”, where in the simplest model the ion velocity parallel to the magnetic field equals the local sound velocity. After reviewing the basic time-independent and collisionless models of the magnetized PWT, various extensions will be discussed which are due to
E
×
B
, ∇
B and diamagnetic drifts, nonuniformity of the electric field parallel to the wall, and turbulence effects. In practically all cases considered, quantitative results can be obtained only by massive application of numerical methods of solution.
The structure of stationary electron–positive ion plasmas in spatially limited vessels is analysed with special emphasis on the plasma–wall transition using different physical models. Basic ...investigations are carried out in a two‐fluid model, which is supplemented by ionization and oblique magnetic fields. Collisions between the two particle species were taken into account, as well as the dependence of the collision frequency on the particle density. For the case of non‐vanishing magnetic fields, electrons are not assumed to be in Boltzmann equilibrium. The investigated one‐dimensional domain is limited by totally absorbing walls on each side. Stationary states are considered, in which ionization sources balance the wall losses. To also take into account kinetic effects, simulations in a quasi‐neutral hybrid model are performed. The hybrid model assumes the electrons as a fluid and treats the ions using a particle‐in‐cell (PIC) method. A new way of ensuring the Bohm criterion is used by removing those superparticles impeding the wall. When comparing the results, both models reveal differences, especially when ionization from a resting neutral gas or weakly magnetized plasmas is considered, causing a broadening of the ion distribution or anisotropy effects, respectively.
The boundary conditions (BCs) involving a plasma-wall transition (PWT) are crucial when estimating the particle and heat fluxes at the wall, and when simulating the edge plasma with fluid, ...gyro-kinetic and gyro-fluid codes. The aim of this work was to derive time-dependent BCs at the PWT for ELM-free, Type-I ELM and post-ELM states based on a kinetic test simulation in the ITER tokamak without neutrals, so as to obtain the steady state. This contribution describes the first results of attempts to address this issue for ITER simulations under high-performance conditions using the 1D3V electrostatic parallel Particle-in-Cell code BIT1 (Tskhakaya in Plasma Phys Control Fusion 59(11401):19pp, 2017). The burning plasma conditions correspond to the ITER Q = 10, 15 MA baseline at
q
95
= 3, for which the poloidal length of the 1D SOL is
∼
20 m from the inner to the outer target, assuming typical upstream separatrix parameters of
n
e
∼
3 to 5
·
10
19
m
-
3
,
T
e
∼
100 to 150 eV and
T
i
∼
200 to 300 eV. Inclined magnetic fields at targets of (
∼
5
∘
) are included, as are the particle collisions, with a total of 3.4
·
10
5
poloidal grid cells, giving shortening factors of 20. The results show that for the ELM-free state the BCs relate to the classic one; in the phase of the Type-I ELM, the BCs are increasing; and in the post-ELM, the BCs are decreasing, reaching the classic values. Taking into account this kind of BC dependence, we can provide realistic ITER plasma profiles for subsequent investigations. As this is a time-consuming process, the simulations are first conducted without neutrals, while in order to obtain realistic values for the BCs, the neutrals are added to the system. At a later stage, these will be used as BCs for the calculations of the ELM target heat loads using the SOLPS-ITER (Bonnin in Plasma Fusion Res 11:1403102, 2016; Wiesen in J Nucl Mater 463:480–484, 2015) code.
