Cameron Samuell

Plasma parameters and electron energy distribution functions in a magnetically focused plasma

Spatially resolved measurements of ion density, electron temperature, floating potential, and the electron energy distribution function (EEDF) are presented for a magnetically focused plasma. The measurements identify a central plasma column displaying Maxwellian EEDFs at an electron temperature of about 5 eV indicating the presence of a significant fraction of electrons in the inelastic energy range (energies above 15 eV). It is observed that the EEDF remains Maxwellian along the axis of the discharge with an increase in density, at constant electron temperature, observed in the region of highest magnetic field strength. Both electron density and temperature decrease at the plasma radial edge. Electron temperature isotherms measured in the downstream region are found to coincide with the magnetic field lines.

Spatiotemporal Pattern Formation in an Atmospheric Plasma Discharge

We have developed a radio-frequency-powered non-equilibrium argon gas discharge consisting of two parallel electrodes, with at least one being covered with a thin dielectric layer. The atmospheric discharges that take place in such an experimental device are of different types, depending on the experimental conditions, particularly on the product pd of gas pressure p and discharge width d. Spatiotemporal pattern formations and microdischarge phenomena occurring in this atmospheric plasma discharge have been studied by using a high-resolution video camera. In particular, we observe moving fingerlike structures, occurring as the argon plasma expands radially across the electrodes, which are indicative of fluidlike behavior. Other spatiotemporal phenomena include traveling localized and starlike discharges. All of the observed phenomena can be controlled by varying the RF input power, gas flow, and discharge gap size.

Atomic and molecular hydrogen gas temperatures in a low-pressure helicon plasma

Neutral gas temperatures in hydrogen plasmas are important for experimental and modelling efforts in fusion technology, plasma processing, and surface modification applications. To provide values relevant to these application areas, neutral gas temperatures were measured in a low pressure (10 mTorr) radiofrequency helicon discharge using spectroscopic techniques. The atomic and molecular species were not found to be in thermal equilibrium with the atomic temperature being mostly larger then the molecular temperature. In low power operation (1 kW), the molecular hydrogen temperature was observed to be linearly proportional to the pressure while the atomic hydrogen temperature was inversely proportional. Both temperatures were observed to rise linearly with input power. For high power operation (5–20 kW), the molecular temperature was found to rise with both power and pressure up to a maximum of approximately 1200 K. Spatially resolved measurements near a graphite target demonstrated localised cooling near the sample surface. The temporal evolution of the molecular gas temperature during a high power 1.1 ms plasma pulse was also investigated and found to vary considerably as a function of pressure.