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Benchmarks of the new 1D2V kinetic code KIPP (KInetic code for Plasma Periphery) for parallel plasma transport in the scrape-off layer (SOL) and divertor of magnetic confinement fusion devices are presented. The code is based on the continuum discretisation scheme for the Vlasov-Fokker-Planck equation. It assumes plasma quasi-neutrality, maintained by the electron parallel momentum balance, and uses a logical sheath boundary condition for the Debye potential drop at material surfaces. The code is parallelized under the MPI environment, with the most time consuming part, Coulomb collisions, being calculated simultaneously for all spatial locations by separate processors using a sparse matrix solver for the full non-linear collision operator in two velocity variables: parallel and gyro-averaged perpendicular velocities. KIPP is being developed with the aim of integrating it into SOLPS (B2-Eirene), to replace fluid treatment of parallel plasma transport with the kinetic one. Benchmark results for parallel electron heat conduction and electron-ion thermoforce for highly collisional plasmas are presented, as well as some results for less collisional plasmas. This paper focuses on the 1d2v features of the code, with the 0d2v features presented earlier in [1, 2].

A new kinetic code is presently being developed at IPP Garching to describe parallel (along magnetic field lines) plasma transport in the SOL and divertor of tokamaks. The development of the code is aimed at replacing parallel transport equations used in the present day fluid codes such as SOLPS(B2), EDGE2D, UEDGE. The code is based on the continuum discretisation scheme for the Fokker-Planck equation for parallel plasma transport. In the physical space (along B-lines) the fine spatial structure on the scale of the Debye length is not resolved, instead, plasma quasi-neutrality on a much longer scale, controlled by the parallel electron momentum balance equation, is assumed. At the interface with a material surface, the logical sheath condition is used. The code initially is 1D2V, with parallel and gyro-averaged perpendicular velocities being independent velocity variables. In the future, extension of the kinetic treatment on ions, and extension of the code dimensionality to 2D2V to cover also radial (across magnetic field lines) dimension is envisaged. Details of the code, together with its benchmarking by comparing code results with analytical theory in the limit of highly collisional plasmas, are presented in the paper (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

As part of a general effort in validating SOL fluid Monte Carlo codes, well diagnosed ohmic discharges have been done in ASDEX Upgrade reaching from the lowest accessible density up to densities at which both targets were at least partially detached. The numerical code B2.5-EIRENE has been used to simulate these experiments with a particular focus on detachment. Whilst it is possible to qualitatively reproduce the general experimental observations when transiting from attached to detached plasmas, the simulations do not reproduce the detachment threshold observed in experiment quantitatively. The strong asymmetry of the ion flux density between the inner and the outer target with increasing density and in particular the vanishing ion flux, defined as full detachment, at the inner target cannot be reproduced. The influence of various parameters such as chemical sputtering yields and the effect of the activation of drift terms on the results is analyzed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The plasma turbulence in the boundary of fusion relevant experiments is known to have a quasi two-dimensional nature: the scale lengths perpendicular to the magnetic field are in the order of mm to cm, but parallel to the magnetic field, the correlation lengths are in the order of several meters. Recent parallel correlation studies with Langmuir probes at the JET tokamak over very long connection lengths (23 m and 66 m probe tip separation along the magnetic field) showed a correlation of less than 50 %, in contrast to the finding of 80-90 % correlation in other devices at measurements with smaller probe tip separations. However, it was not clear if this is a genuine physical property of the electrostatic turbulence in the scrape-off layer or whether perturbations in the magnetic configuration had caused an additional decorrelation by a time-dependent misalignment of the two probe tips along the connecting field line. In this contribution we analyze the effect of such perturbations in the magnetic configuration on the parallel correlation measurements in a simple model and compare the results with those of the measurements at JET.

Magnetic induction becomes important when the skin-depth equals the wavelength of the electrostatic drift turbulence: . It is predicted that this suppresses the longwave perturbations responsible for the bulk of the turbulent transport, providing an explanation for the L-H transition. Since k⟂ρs ≪ 1 at the edge (ρs - ion Larmor radius), this may occur at rather low β, typical of the separatrix parameters. The above equality is used to derive thresholds for the L-H transition: β ≈ (k⟂ρs)2(me/mi)in the collisionless skin-depth limit of very low density plasmas and (L⟂-perpendicular decay length) in the collisional skin-depth limit of medium to high density plasmas. The latter is in a broad agreement with experiment, pointing to a possible role of low temperature collisional plasma (which is in the SOL) in the physics of the L-H transition.

The various particle and energy drift fluxes are presented, and it is shown that the divergence-free part of the diamagnetic terms do not contribute to the fluid equations. In particular, it is shown that the ⊇TxB heat flux (the so-called Hinton-Staebler term) cancels exactly from the energy equation. The implementation of the drift fluxes into the EDGE2D code is described and some results of preliminary code runs indicated.

In this paper, results from the array of fixed Langmuir probes in the JET Mark I divertor are presented. During low density discharges there is good agreement between single and triple probes. At higher density, near the onset of divertor detachment, very low values of the electron to ion saturation current (even < 1) are observed which results in an overestimation of the electron temperature, particularly by the triple probe. Alternative methods of probe interpretation are applied and comparisons carried out with independent measurements. The consistency of probe measurements during H-mode discharges are also briefly discussed.