CATHODE-FALL DEVELOPMENT IN LOW-PRESSURE, PARALLEL-PLANE HYDROGEN DISCHARGES

The temporal and spatial development of the cathode fall in pulsed, lo w-pressure hydrogen discharges is investigated using correlated measur ements of the current, voltage, and optical emission. The results incl ude the variation of relative emission probabilities versus time and p osition for the H(n = 3) and H-2(alpha(3) Sigma) states. The behavior of the higher-energy electrons is inferred from the first negative ban d emission of N-2(+) in mixtures of 2-3% N-2 in H-2. Measurements are reported for final, i.e., quasi-steady-state, discharge currents of 10 -100 mA for pressure times electrode spacing (pd) values of 1 and 3 To rr cm, where 1 Torr = 133 Pa. The breakdown electric field E to gas de nsity values vary from 1 kTd to 400 Td, where 1 Td = 1x10(-21) V m(2). The H-alpha and the near-uv continuum emission data show the importan ce of heavy-particle excitation in the cathode-fall region. Representa tive transient current and voltage wave forms during the development o f the cathode sheath are analyzed in terms of discharge and circuit pa rameters. During the period of rapid current growth at 3 Torr cm, tran sient emission wave forms for the uv continuum near the anode show a s udden drop that results from the collapse of the electric field.