Our research in plasma physics has two directions of focus 1) fusion plasmas, which aims to develop an alternative and clean source of energy based on nuclear fusion and 2) materials processing plasmas, directed towards development of plasma processes to produce new materials with tailored properties or modify surfaces with ion implantation. Plasma diagnostics such as laser induced fluorescence (LIF) and electrostatic energy analysis are used to study the properties of plasmas.

> Plasma confinement

Material to be supplied.

> Fusion Plasmas

The unlimited supply of energy promised by the fusion program is yet to be realized, but the first commercial plant will almost certainly be demonstrated this century. We are collaborating with ANU in the Heliac project. This project is trialling a new magnetic field environment for plasma confinement which is a practical alternative to the well-known Tokamak. Work is also underway to develop a small fusion reactor in the Desktop Fusion project.

Contact: A/Prof. Brian James, b.james@physics.usyd.edu.au.

> Desktop Fusion

Another route to fusion which can be demonstrated on a much smaller scale is the so-called "desktop" fusion process. A plasma is generated and the ions are attracted into a central point by an electric field. Because of the spherical symmetry the ions meet at the center of the device, as shown in the figure. Fusion occurs releasing neutrons from the central region.

Contact: Dr Joe Khachan, j.khachan@physics.usyd.edu.au.

> Dielectric barrier discharges

A Dielectric Barrier Discharge (DBD) is a gas discharge between two electrodes separated by one or more dielectric layers and a gas-filled gap. A typical DBD in which the electrodes are both covered with a dielectric layer is shown in the figure. When a high voltage is applied to the electrodes the electric field in the gap ionises the gas. The ions and electrons produced by this electric discharge are attracted towards the electrodes of opposite polarity and form a charge layer on the dielectric surface. These charges cancel the charge on the electrodes so that the electric field in the gap falls to zero and the discharge stops. Devices based on this process have applications in areas as diverse as plasma displays, photo-chemistry and broad area surface treatment in industry such as sterilisation and surface etching.

DBD research program: The Plasma Physics Team is investigating DBDs designed for two applications: DBDs for Plasma Display Panels The application of DBDs with the most commercial potential is the plasma display panel (PDP), a flat, high-resolution TV visual display unit which can be scaled up to produce large pictures. PDPs of >100 cm diagonal for domestic use are currently on the market. We are investigating the growth of the discharge in a small DBD similar to that in a PDP. The picture shows a series of images of the discharge in argon.

Need picture

Efficient high-power ultraviolet lamps DBDs in xenon gas, when driven by very short voltage pulses are efficient sources of UV radiation. We are collaborating with Macquarie University on developing large area xenon DBD lamps for industrial applications.

> Materials processing plasmas

The ions produced in plasmas can be used to modify surfaces and to create new layers or films on surfaces. The effect depends on the ion flux, impact energy and the nature of the ion-surface interaction. The production of diamond is currently under investigation. Previous work has used microwave plasmas but current work is directed towards diamond formation by directing ion beams at the growth surface.

Contact: Prof. Marcela Bilek, mmmb@physics.usyd.edu.au.

> Fuse spectroscopy

Brian James and Ian Falconer are rounding off work on a spectroscopic measurement of the electron temperature and density of the plasma in high-voltage, high current fuses. This work is in conjunction with Tony Stokes from Electrical Engineering at the University of Sydney.

> Laser Induced Fluorescence

The ion energy and electric fields present in a plasma determine the effects which can be achieved in plasma-surface interactions. It is important to investigate these parameters without disturbing the conditions in the plasma. Crossed laser beams can be used to define a localized region in the plasma and generate fluorescent light from the atom-photon interactions. This light has a Doppler shift dependent on the velocity in the line of sight and so can be used to measure the velocities and hence energies of the atoms or ions. A sheath always surrounds an electrode or work-piece being treated in a plasma and determines the ion implantation dose and process stability in Plasma Immersion Ion Implantation (PIII). LIF can reveal the conditions in the sheath without disturbance.