Current balance at an end plate of the GAMMA 10 tandem mirror

A recent mesh bias experiment suggests breaking down of a simple balance between an end-loss electron current and an end-loss ion current. We have found a new current flowing into the endplate from the back side of the endplate. A numerical model is constructed which takes account of this current and mirror reflection of secondary electrons emitted from the endplate off an outer mirror throat. The model self consistently solves the current balance and the endplate potential. The current balance at the endplate is well explained by this model. (author)