Analysis of the tokamak sheath region with in-sheath ionization and transport of surface emitted particles

Journal Article · Tue Nov 01 04:00:00 EST 1994 · Physics of Plasmas; (United States)

DOI:https://doi.org/10.1063/1.870896· OSTI ID:6958871

Hua, T Q; Brooks, J N ^[1]

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1. Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)

A self-consistent numerical analysis has been performed of the oblique incidence magnetic field tokamak sheath, with in-sheath ionization and transport of surface desorbed and reflected hydrogen molecules and atoms, and sputtered and evaporated surface atoms. The analysis uses the newly developed BPHI Monte Carlo/cloud-in-cell kinetic code together with particle--surface interaction models. For typical plasma boundary conditions ([ital T][sub [ital e]]=100 eV, [ital n][sub [ital e]]=1[times]10[sup 20] m[sup [minus]3]), nearly all desorbed hydrogen molecules are ionized in the sheath; this lowers sheath potential by up to 30% and increases heat transmission by up to 150%. Backscattered hydrogen, and elastic collisions between primary ions and hydrogen molecules, in contrast, have a negligible effect on sheath parameters. The magnetic sheath region has a significant effect on sputtered tungsten atoms, resulting in high local redeposition, but is not itself changed by the sputtering. Ionization of thermally evaporated surface atoms (from overheating) can increase sheath heat transmission significantly, a process which may contribute to surface hot-spot formation.

• OSTI ID: 6958871
• Journal Information: Physics of Plasmas; (United States), Journal Name: Physics of Plasmas; (United States) Vol. 1:11; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700330 -- Plasma Kinetics
Transport
& Impurities-- (1992-)
700350* -- Plasma Production
Heating
Current Drive
& Interactions-- (1992-)
CALCULATION METHODS
CLOSED PLASMA DEVICES
ELEMENTS
EQUATIONS
HOT SPOTS
HYDROGEN
IMPURITIES
IONIZATION
KINETIC EQUATIONS
METALS
MONTE CARLO METHOD
NONMETALS
NUMERICAL SOLUTION
PLASMA IMPURITIES
PLASMA SHEATH
SPUTTERING
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TRANSITION ELEMENTS
TRANSPORT THEORY
TUNGSTEN