One-dimensional particle-in-cell simulation of a current-free double layer in an expanding plasma

A one-dimensional particle-in-cell code using Monte Carlo collision techniques (MCC/PIC) for both ions and electrons is used to simulate our earlier experimental results which showed that a current-free electric double layer (DL) can form in a plasma expanding along a diverging magnetic field. These results differ from previous experimental or simulation systems where the double layers are driven by a current or by imposed potential differences. Both experiment and simulation show accelerated ions with energies up to about 60 eV on the low potential side of the plasma. A new numerical method is added to the conventional PIC scheme to simulate inductive electron heating, as distinct from the more common capacitively driven simulations. A loss process is introduced along the axis of the simulation to mimic the density decrease along the axis of an expanding plasma in a diverging magnetic field. The results from the MCC/PIC presented here suggest that the expansion rate compared to the ionization frequency i...