Asymptotically correct collisional presheaths. Report for 1 September 1985-19 August 1987

Technical Report · Mon Jun 01 04:00:00 EDT 1987

OSTI ID:5264841

Main, G L

Few exact solutions for collisional presheaths exist because of the difficulty of simultaneously satisfying both the collisional Boltzmann equation and the Poisson equation. The exact solutions that do exist are for very specialized collision terms such as constant cross-section charge exchange with cold neutrals. This paper presents an asymptotic method which is applicable to a variety of collision terms and is applied in particular to constant collision-frequency charge exchange with noncold neutrals. Constant collision frequency and constant cross-section collision with cold-neutral results are also presented. The first order terms for the presheath potential rise and ion distribution functions are calculated and it is shown that second- and higher-order terms can be calculated using a multiexponential expansion for presheath potential rise. The first-order cold-neutral constant cross-section results correspond well to the exact solution. The calculated presheath potential rises are of the order expected from the Bohm criterion, and in some of the specialized cold-neutral cases, exactly k/sub e/2. The presheath potential rise is reduced by a neutral-plasma potential gradient that accelerates ions toward the presheath. In all cases the collisional presheath is asymptotically matched to both the neutral plasma and the collisionless sheath

• Research Organization: Georgia Inst. of Tech., Atlanta (USA). School of Mechanical Engineering
• OSTI ID: 5264841
• Report Number(s): AD-A-189531/7/XAB
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700103 -- Fusion Energy-- Plasma Research-- Kinetics
74 ATOMIC AND MOLECULAR PHYSICS
BOHM CRITERION
BOLTZMANN EQUATION
CHARGED PARTICLES
COLLISIONS
CROSS SECTIONS
DIFFERENTIAL EQUATIONS
DISTRIBUTION FUNCTIONS
EQUATIONS
FUNCTIONS
IONS
LOW TEMPERATURE
PARTIAL DIFFERENTIAL EQUATIONS
POISSON EQUATION