skip to main content

SciTech ConnectSciTech Connect

Title: Fluid model of the sheath in front of a floating electrode immersed in a magnetized plasma with oblique magnetic field: Some comments on ion source terms and ion temperature effects

A one-dimensional fluid model of the magnetized plasma-wall transition region in front of a floating electrode immersed in a magnetized plasma with oblique magnetic field is presented. The Boltzmann relation is assumed for the electrons, while the positive ions obey the ion continuity and momentum exchange equation. The ions are assumed to be isothermal. By comparison with a two-fluid model, it is shown that assuming the Boltzmann relation for the electrons implies that there is no creation or annihilation of the electrons. Consequently, there should not be any creation and annihilation of the positive ions either. The models that assume the Boltzmann relation for the electrons and a non-zero ion source term at the same time are therefore inconsistent, but such models have nevertheless been used extensively by many authors. So, in this work, an extensive comparison of the results obtained using the zero source term on one hand and three different non-zero source terms on the other hand is made. Four different ion source terms are considered in total: the zero source term and three different non-zero ion source terms. When the zero source term is used, the model becomes very sensitive to the boundary conditions, and in somemore » cases, the solutions exhibit large amplitude oscillations. If any of the three non-zero ion source terms is used, those problems are eliminated, but also the consistency of the model is broken. The model equations are solved numerically in the entire magnetized plasma-wall transition region. For zero ion temperature, the model can be solved even if a very small ion velocity is selected as a boundary condition. For finite ion temperature, the system of equations becomes stiff, unless the ion velocity at the boundary is increased slightly above the ion thermal velocity. A simple method how to find a solution with a very small ion velocity at the boundary also for finite ion temperature in the entire magnetized plasma-wall transition region is proposed.« less
Authors:
 [1] ;  [2] ;  [3]
  1. University of Ljubljana, Faculty of Electrical Engineering, Tržaška 25, 1000 Ljubljana (Slovenia)
  2. (Slovenia)
  3. Jožef Stefan Institute, Jamova 39, POB 100, 1000 Ljubljana (Slovenia)
Publication Date:
OSTI Identifier:
22408363
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 4; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AMPLITUDES; ANNIHILATION; BOLTZMANN EQUATION; BOUNDARY CONDITIONS; CATIONS; ELECTRODES; ELECTRONS; FIRST WALL; FLOW MODELS; ION SOURCES; ION TEMPERATURE; MAGNETIC FIELDS; MATHEMATICAL SOLUTIONS; ONE-DIMENSIONAL CALCULATIONS; OSCILLATIONS; PLASMA; PLASMA SHEATH; SOURCE TERMS; TEMPERATURE DEPENDENCE