Henning wrote: As far I understood Eric, the effect of the axial coil in FF1 is to get the plasma sheath into filaments as early as possible.
That’s what the tungsten “crown” at the base of the anode is meant to do… encourage the start of filamentation in the sheath.
The axial field is meant to impart a small rotational component to the sheath/filaments as they travel down the electrodes so that when the pinch comes the filaments more readily swirl into a vortex rather than clashing together and thus losing energy.
