Revisited global drift fluid model for linear devices

Abstract

The problem of energy conserving global drift fluid simulations is revisited. It is found that for the case of cylindrical plasmas in a homogenous magnetic field, a straightforward reformulation is possible avoiding simplifications leading to energetic inconsistencies. The particular new feature is the rigorous treatment of the polarisation drift by a generalization of the vorticity equation. The resulting set of model equations contains previous formulations as limiting cases and is suitable for efficient numerical techniques. Examples of applications on studies of plasma blobs and its impact on plasma target interaction are presented. The numerical studies focus on the appearance of plasma blobs and intermittent transport and its consequences on the release of sputtered target materials in the plasma. Intermittent expulsion of particles in radial direction can be observed and it is found that although the neutrals released from the target show strong fluctuations in their propagation into the plasma column, the overall effect on time averaged profiles is negligible for the conditions considered. In addition, the numerical simulations are utilised to perform an a-posteriori assessment of the magnitude of energetic inconsistencies in previously used simplified models. It is found that certain popular approximations, in particular by the use of simplified vorticity equations, do not significantly affect energetics. However, popular model simplifications with respect to parallel advection are found to provide significant deterioration of the model consistency. [http://dx

A plasma source driven predator-prey like mechanism as a potential cause of spiraling intermittencies in linear plasma devices

“…15. The equations of continuity, parallel momentum, and electron temperature describing the global profiles temporal evolution of particle density n, parallel electron velocity v jj , parallel ion velocity u jj , and electron temperature T e read @n @t…”

“…4,5 The numerical approach is based on an electrostatic drift fluid model for electrons and ions in a cylindrical geometry with ions assumed to be cold, T i ( T e , and electromagnetic effects assumed to be negligible, b ( 1. Drift fluid models and variants thereof (sometimes denoted as drift-reduced Braginskii models, reduced MHD models, or resistive drift wave models) are widely used for theoretical studies of plasmas in linear devices [6][7][8][9][10][11][12][13][14][15][16] and have been proven successful in the analysis and interpretation of experimental findings on statistical properties, plasma structures, instability drive, and the sensitivity of plasma dynamics on plasma sources, device dimensions, ion-neutral collisions. The particular approaches differ, e.g., in their dimensionality (2D or 3D in space), their use of scale separation (local or global approach), the treatment of axial boundary conditions (sheath conditions or periodic boundary conditions), the inclusion of non-linear dynamics (linear or non-linear models), the inclusion of electron temperature evolution (constant temperature or timedependent profiles), and the details of plasma sources (uniform in axial direction or localized).…”

“…For the axial end of the cylinder, Bohm sheath boundary conditions are imposed. 15,16 The simulations focus on the formation of spiraling intermittencies and their underlying dynamics. It is found that an imbalance of the electron pressure gradient and the parallel electric field in the plasma source region is the origin of the coherent structures observed.…”

Hermes: global plasma edge fluid turbulence simulations

“…This is an ambitious undertaking, as it requires the combination of neutral gas and atomic physics, plasma-wall interaction, turbulent transport, and neoclassical effects [11]. As a first step towards this, we present in section 2 a drift-reduced model [12,13,14,15] which has been constructed based on the derivation of Simakov and Catto [16], and similar to that derived in [17] but with several modifications to make it more suitable for numerical solution in global geometry. This model has good conservation properties, described in section 2.1, and has been implemented using the BOUT++ framework [18,19] using conservative numerical methods described in section 3.…”

Mode Structure Analysis of Detached Plasmas with 2D Images

“…In the linear plasma device NAGDIS-II (NAGoya DIvertor plasma Simulator II), fast framing camera observations have revealed that a spiral structure ejected from the plasma column was rotated in E × B direction in the peripheral region of the plasma column, where the electric field was in the radial direction [4,10]. Recent three dimensional simulation aiming at linear plasma devices predicted that resistive drift instability leads to generation of blob-like structures [11]. From the simulation, it was also suggested that the instability with m = 0 mode in the core region of the cylindrical plasma was important for the spiral structure formation in linear devices in addition to the instability with m = 1 author's e-mail: kajita.shin@nagoya-u.jp mode [12].…”