Numerical simulation of electric double layers in a helicon plasma device

We have studied formation of Current Free Double Layers (CFDLs) in a highly diverging magnetic field by means of two-dimensional electrostatic particle in cell simulations. This study is motivated by laboratory experiments on CFDLs in Helicon Plasma Device. Since CFDLs accelerate ions, the experimental work has led to design of a new generation of plasma thrusters known as Helicon Double Layer Thrusters. CFDL structure consists of U-shaped equipotentials and a conical plasma density structures. The physical processes leading to these structures are critically studied. We found that the difference in the magnetization of electrons and ions in the plasma plays key role in the generation of the density and potential structures. Features of ion acceleration responsible for thrust generation are studied. The potential and the density structures and the electric field strengths in the CFDL are in good agreements with the laboratory experiments.