Double layers (DLs) have been observed in a plasma reactor composed of a source chamber attached to a larger expanding chamber. Positive ion beams generated across the DL were characterized in the low plasma potential region using retarding field energy analyzers. In electropositive gases, DLs were formed at very low pressures (between 0.1 and 1 mTorr) with the plasma expansion forced by a strongly diverging magnetic field. The DL remains static, robust to changes in boundary conditions, and its position is related to the magnetic field lines. The voltage drop across the DL increases with decreasing pressure, i.e. with increasing electron temperature (around 20 V at 0.17 mTorr). DLs were also observed in electronegative gases without a magnetic field over a greater range of pressure (0.5 to 10 mTorr). The actual profile of the electronegative DL is very sensitive to external parameters and intrusive elements, and they propagate at high negative ion fraction. Electrostatic probes measurements and laser induced photodetachment show discontinuities in all plasma parameters (electron density, electron temperature, negative ion fraction) at the DL position. The voltage drop across the electronegative DL is about 8 V, is independent of the gas pressure and therefore of the electron temperature.

The Magnetized Plasma Interaction Experiment (MAGPIE) is a versatile helicon source plasma device operating in a magnetic hill configuration designed to support a broad range of research activity and is the first stage of the Materials Diagnostic Facility at the Australian National University. Various material targets can be introduced to study a range of plasma-material interaction phenomena.Initially, with up to 2.1 kW of RF at 13.56 MHz, argon (10 18 -10 19 m −3 ) and hydrogen (up to 10 19 m −3 at 20 kW) plasma with electron temperature ∼3-5 eV was produced in magnetic fields up to ∼0.19 T. For high mirror ratio we observe the formation of a bright blue core in argon above a threshold RF power of 0.8 kW. Magnetic probe measurements show a clear m = +1 wave field, with wavelength smaller than or comparable to the antenna length above and below this threshold, respectively. Spectroscopic studies indicate ion temperatures <1 eV, azimuthal flow speeds of ∼1 km s −1 and axial flow near the ion sound speed.

A reproducible instability, which appears similar to those reported previously, has been observed and studied in a low-pressure 13.56 MHz inductively coupled gaseous electronics conference rf cell operating in oxygen. The instability has been observed in the form of periodic modulations in the light output, floating potential, electron and positive and negative ion densities. The magnitude and frequency of the modulations is sensitive to the plasma operating conditions and the modulation amplitude has been observed to be as high as 40%. The instability is observed in a pressure and power regime where both the capacitive and inductive modes can exist. The frequency of the oscillations increases with increase in gas pressure from 3 to 21 kHz. This pressure window coincides with the pressure regime where there exists a significant fraction of negative ions in both modes. Time-resolved measurements of the electron energy distribution functions and charged particle densities indicate that at all phases of the instability, the plasma parameters remain close to those of the inductive mode. A global model has been modified for an oxygen discharge and this provides a qualitative description of the instability. The global model predicts a smaller power and pressure window for the instability but it can provide a framework for the discussion of instabilities in weakly electronegative discharges.

Double-layers (DLs) were observed in the expanding region of an inductively coupled plasma with Ar/SF 6 gas mixtures. No DL was observed in pure argon or SF 6 fractions below few percent. They exist over a wide range of power and pressure although they are only stable for a small window of electronegativity (typically between 8% and 13% of SF 6 at 1mTorr), becoming unstable at higher electronegativity. They seem to be formed at the boundary between the source tube and the diffusion chamber and act as an internal boundary (the amplitude being roughly 1.5 kTe e )between a high electron density, high electron temperature, low electronegativity plasma upstream (in the source), and a low electron density, low electron temperature, high electronegativity plasma downstream.