When electrodes are biased above the plasma potential, electrons accelerated through the
associated electron sheath can dramatically increase the ionization rate of neutrals near the
electrode surface. It has previously been observed that if the ionization rate is great enough,
a double layer separates a luminous high-potential plasma attached to the electrode surface
(called an anode spot or fireball) from the bulk plasma. Here, results of the first 2D particle-in-
cell simulations of anode spot formation are presented along with a theoretical model …