Microstructured Electrode Arrays: Optical Analysis of the Glow Discharge in a Magnified Electrode Gap

The characterisation of a discharge requires the knowledge about few parameters. The most important are the electron density, the debye-length λd and the voltage/current characteristic. Normally the electron density is obtained using a Langmuir Probe. This method delivers reliable results if the influence on the electric field can be neglected. In the analysis of microdischarges, this assumption is not fulfilled. J. Park et al. (J. Appl. Phys.2001, 89, 15), developed a model which allows to calculate the electron density using the plasma current, the area of the discharge and the electric field strength. The debye-length can be estimated using the dimensions of the dark space of the discharge. With this information it is possible to calculate the electron temperature. To measure the dimension of the dark space, it is crucial to take a close look at the discharge. We used an ocular of a microscope (40× magnification) to project an image of one electrode gap onto the sensor of an ICCD-Camera. The electrical parameters were obtained using an ENI V/I-Probe®. The experiments were conducted in helium and argon at atmospheric pressure. In order to cover the whole glow-discharge regime, the applied power was raised in steps of 1 W from the point of ignition to the glow-to-arc transition. Electron densities and temperatures as well as the debye-length could be obtained.