Study of striations in a spherically symmetric hydrogen discharge

Experiments on a high power spherically symmetric positive corona discharge in molecular hydrogen are reported upon. These are collisional plasmas in the H2 pressure range of about 0.75 Torr to 3 Torr. Applied voltages ranged up to 600 V on the anode with currents ranging up to 3 A. As others have observed in prior published experiments going back to 1997, we have observed spherically symmetric striations or double layers. Others have observed such striations in O2, CO2, and in mixtures of N2 and acetone or methanol, or benzene. Like H2 all these gases, except N2 itself, readily dissociate and form negative ions by dissociative attachment with electrons. We propose that the striations are instabilities arising from copious formation of negative ions that modify the radial space charge and electric field distributions in such high aspect ratio spherical discharges.