Ignition of a nanosecond-pulsed near atmospheric pressure discharge in a narrow gap

Sarah Müller (1) , Dirk Luggenhölscher (1) , Uwe Czarnetzki (1)

1 Institute for Plasma and Atomic Physics

The ignition phase and the transition to quasi DC glow operation of a narrow-gap near atmospheric pressure discharge in hydrogen are investigated experimentally . The discharge is ignited by a short 10 ns voltage pulse with a peak voltage of 1.3 kV followed by a 150 ns plateau of about 350 V. Pulsing is at 12 kHz which leaves a significant amount of residual charge between the individual pulses. Temporally resolved laser electric field measurement in the centre of the discharge employing a non-linear four-wave mixing scheme, ultra-high speed optical imaging by an ICCD camera at Balmer-alpha and Fulcher lines as well as the undispersed emission, and current and voltage measurements are performed. Special emphasis is put on a detailed analysis of the measured data by combining the results from the various diagnostics. This allows in addition to the directly measured quantities determination of the absolute evolution of the electron density, the development of space charge shielding, and the observation of the local electron dynamics. Pressure variations in a limited range indicate reasonable agreement with the Paschen law but raise also questions on the definition of the break down voltage under highly transient conditions. 2 Atmospheric pressure discharges under small spatial dimensions, so called microplasmas , have attracted large attention in recent years. On one hand large expectations on industrial applications exists while on the other hand the physics is often complex and difficult to investigate. In particular diagnostics is a challenge since most of the tools and techniques developed over decades for low-pressure, large scale discharges can not be applied here. Many types of microplasmas operate in pulsed mode and the transient phase of their ignition is even more difficult to access by adding to the already microscopic dimensions also fast temporal changes on ns or sub-ns timescales. Here an experimental investigation of the rapid ignition phase and the subsequent transition to quasi-DC operation in a molecular gas (hydrogen) is reported. The geometry is one-dimensional to allow a simple interpretation. The main parameters determined directly are the discharge voltage, the current density, the electric field in the centre of the discharge, and the spatially and temporally resolved emission. First successful application of these diagnostics to a similar setup was reported in [ 1-3 ]. Here we go beyond by more detailed studies and in particular a careful analysis and interpretation of the data. From the combination of the directly measured quantities with simple and robust models further insight in the ignition dynamics is provided. The temporal evolution of absolute electron densities is obtained and spatial and temporal development of different groups of low and highly energetic electrons is observed.

Mots clés: Physical Sciences

Sarah Müller, Dirk Luggenhölscher, Uwe Czarnetzki. Ignition of a nanosecond-pulsed near atmospheric pressure discharge in a narrow gap. Journal of Physics D: Applied Physics, 2011, 44 (16), pp.165202. ⟨10.1088/0022-3727/44/16/165202⟩. ⟨hal-00613268⟩