AVS 52nd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS+MS-ThM

Paper PS+MS-ThM8
Computational Model for Ion Beam Extraction from a Pulsed Plasma Through a Grid

Thursday, November 3, 2005, 10:40 am, Room 302

Session: Process Equipment Modeling
Presenter: S.-K. Nam, University of Houston
Authors: S.-K. Nam, University of Houston
V.M. Donnelly, University of Houston
D.J. Economou, University of Houston
Correspondent: Click to Email
A computational model was developed to study the energy and directionality of an ion beam extracted from a pulsed plasma through a grid. First, a fluid model was used to obtain the space and time resolved profiles (at the periodic steady state) of the active glow (power ON) of the 13.56 MHz plasma. Then, the plasma evolution in the afterglow (power OFF) was followed with the fluid model. A positive DC bias voltage (acceleration voltage) was applied at a specific time in the afterglow to raise the plasma potential and expel positive ions out of the plasma and through the grounded extraction grid. The electric potential profiles found by the fluid model were in turn used as a boundary condition in a Particle-in Cell (PIC) simulation of ion flow through the holes of the grid. The output of the PIC simulation was the energy and angular distributions of the extracted ion beam. Fractional beam neutralization by ion contact with the metal grid was also determined. Beam directionality improved by extracting ions in the afterglow as the electron temperature dropped precipitously. A smaller diameter of the grid holes and a greater DC acceleration voltage also improved beam directionality. The energy distribution of the beam was very sharp (assuming ideal step accelerating voltage) except at higher pressures when ion-neutral collisions played a role. Work supported by NSF-NIRT and the Texas Advanced Technology Program.