The development of high-density plasmas is important to a range of application such as rapid material processing for plasma material interaction studies, negative ion sources, neutral beam injections, fundamental plasma studies and space thruster propulsion research. In this thesis, a high-power large volume helicon plasma device, MAGPIE2, is developed and studied. Building on the program established on its smaller predecessor MAGPIE1 device (Magnetized Plasma Interaction Experiment), the high-power plasma capability of MAGPIE2 will provide extreme conditions that wall materials will be exposed to in the next-generation nuclear fusion devices such as ITER (ne=1020 m-3-1021 m-3, Te= 1-10 eV). 

The plasma source of MAGPIE2 is a 200 mm diameter tube manufactured from the highly thermally conductive material aluminium nitride (AlN). The plasma is created by supplying radio frequency power up to 40 kW to specially designed water-cooled antennas that surrounds the AlN source tube. There are three key aspects to this research: (1) Optimisation of the helicon source under different conditions; (2) Investigate helicon wave excitations effects on the plasma productions; (3) Investigate the characteristics of plasma generation with heavy and light ions. In this project, a single loop antenna and a right-hand half helical antenna are studied and compared. The plasma production and electromagnetic wavefields due to helicon wave excitation are studied for both antennas for light ion (hydrogen) and heavy ion (argon) plasmas using a range of diagnostic systems including Langmuir probes, Bdot probes and optical emission imaging. A global model is developed and used to compare the power dependence on the density measurements while the measured wavefields of the plasma are compared with an electromagnetic wavefield model.

It is found that high densities of ~1019 m-3 in argon and ~1018 m-3 in hydrogen can be obtained in the source region with both antennas. In the source region, the densities saturate at high RF powers and at high divergent magnetic fields. However, the half helical antenna shows better plasma production in the downstream compared to the loop antenna. The density in the target region for the half helical antenna continues to increase with increasing power even though the magnetic field strength is low in the downstream region and is shown to be due to enhanced helicon wave activity. Besides that, the discharges also display mode transitions while varying RF power, pressure and the external magnetic field, which is characterized by a significant increase in the on-axis electron density and the plasma emission, as well as the formation of helicon waves. Excellent agreement is found between experiment and modelling. The underlying physics of plasma production and transport is discussed for both light and heavy ion plasmas.

Join the Zoom Meeting
Meeting ID: 847 259 0817
Password: 874 357