The electrical breakdown of plane parallel steel electrodes (10 cm dia
m) is studied in a Pyrex-walled vacuum chamber (minimum pressure less
than 8 x 10(-6) Torr). For clean gases, H-2 and D-2, and with electrod
e gaps from 0.5 to 8 cm, the breakdown at pressures from 0.3 to 0.5 To
rr is consistent with a secondary process of electron release by ion b
ombardment. The breakdown curves for the two gases, when scaled on bot
h axes, overlap to a considerable extent. (C) 1997 American Institute
of Physics.