Philippe Leprince

A Small Microwave Plasma Source for Long Column Production without Magnetic Field

A new HF device is described. It allows the production, without the use of a magnetic field, of long plasma columns from a small HF coupling structure situated at one end of the column. Its operation is based on the propagation of a cold plasma surface wave. This device can work (in argon for example) at pressures from 2 mTorr to 20 Torr with electron densities from 1010 cm-3 to 1013 cm-3, depending on plasma diameter and HF power. Typically, 80W of 500 MHz HF will produce a 25 mn diameter column of 1.8 m length. The plasma is quiescent (low electron density fluctuations), efficient (~ 100% absorbed power), and perfectly reproducible. It can be used as a substitute for a positive column, and some practical applications are foreseen in ion production, laser excitation, gas preionization and spectroscopic sources.

Design of a Microwave Microplasma Source at Atmospheric Pressure

This paper studies two linear resonator sources, which use a continuous 2.45-GHz microwave excitation to produce stable microplasmas, in air and in argon, at atmospheric pressure. The discharges are produced and sustained within the 50-200-mum gap created between two metal electrodes with either 6 or 14 mm in length. Particular attention is given to the design and optimization of the sources (in terms of frequency tuning and power coupling), following a complementary approach based on simulations and experiments. Optical-emission-spectroscopy diagnostics allow one to deduce the rotational, vibrational, and excitation gas temperatures and the electron density (using Stark broadening measurements of the Hbeta line-emission profile).

Images of Atmospheric-Pressure Microplasmas Produced by Continuous 2.45-GHz Excitation

This paper presents an imaging analysis of stable microplasmas produced in air, argon, and helium at atmospheric pressure, using a continuous microwave (2.45-GHz) excitation. The source is a linear-type resonator similar to a microstrip line. The microplasma develops within the 50-200-μm gap created between two metal electrodes (6 mm in length), placed at the open end of the transmission line. Images allow visualizing some of the plasma features and estimating the plasma volumes and, hence, the maximum power density coupled to the plasma.