Simulations of negative ion plasma sheaths.
The need to accurately model beams of negative ions in high current sources makes reasonable to refine the simulation mesh up to fractions of the Debye length lambda(D), which is typically 0.01 mm. Even if simulations were finally possible in two space dimensions, still the role of one-dimensional (1D) model to clarify the physics of sheath and presheath structure and the stability of numerical solvers is fundamental. Here a 1D model with negative ion production from the extraction wall/grid is considered, coupled to a driver plasma which acts as an electron and proton reservoir at a variable plasma potential. A bias voltage between lateral walls and the extraction wall is also included. Particle motion is modeled with diffusion equations, also for protons; electrons are magnetized and Poisson equation is solved everywhere. The inverted sheath formation and the H(-) forward current result sensitive to bias voltage.
Cavenago
M
M
INFN-LNL, viale dell'Universita n. 2, 35020 Legnaro (PD), Italy. cavenago@lnl.infn.it