Michael Pachuilo

Development of a gas-fed plasma source for pulsed high-density plasma/material interaction studies

A gas-fed capillary plasma source has been developed to study plasma-surface interactions under pulsed high pressure arc conditions, without the use of an exploding fuse wire or ablative liner. A nonintrusive preionization source has been developed to break down relatively large interelectrode gaps at low charge voltages of 2-6 kV. The preionization source comprises a nonequilibrium surface streamer discharge that forms a conducting channel through which the main thermal arc discharge is initiated. The arc electron temperature and number density are estimated to be Te ~ 1-2 eV and ne ~ 1023 m-3. Silicon and sapphire samples were exposed to the arc plasma and revealed deposition of electrode and wall materials. Substitution of Elkonite 50W3 for brass electrodes reduced plasma contamination to acceptable levels. The plasma-material interactions were examined and quantified using scanning electron microscopy and energy dispersive X-ray spectroscopy.

Population of vibrational levels of carbon dioxide by cylindrical fast ionization wave

The population of vibrational levels of carbon dioxide (CO2) by a cylindrical fast ionization wave is analyzed using a one-dimensional Particle-in-Cell Monte Carlo collisions model. The model takes into account the inelastic electron-neutral collisions as well as the super-elastic collisions between electrons and excited species. We observe an efficient population of only the first two levels of the symmetric and asymmetric vibrational modes of CO2 by means of a fast ionization wave. The excitation of other higher vibrational modes by the fast ionization wave is inefficient. Additionally, we observe a strong influence of the secondary electron emission on the population of vibrational states of CO2. This effect is associated with the kinetics of high energy electrons generated in the cathode sheath.

Arc breakdown in high-pressure large gap sources using surface streamer based initiation

A non-equilibrium atmospheric streamer discharge has been investigated as a means to seed a large gap arc breakdown. The dynamics of a surface streamer discharge has been analyzed with high speed imaging, voltage and current characterization as well as light intensity measurements. The temporal evolution of the discharge has been examined and a mechanism for the formation and propagation of the discharge presented. Thermodynamic properties of the atmospheric streamer discharge were determined from a time and spatially averaged spectra and a collisional-radiative model. The electron temperature and density were measured to be 1.25 eV and 10 m respectively. The velocity of the surface streamer was estimated to be ~110 km/s with a diameter of ~400 μm.

Development of a high-power capillary discharge for studying ablation at the micron scale

Summary form only given. The objective of this work is to develop a capillary discharge for studying (at a very fundamental level) the processes by which materials ablate when exposed to cold (1-3 eV) thermal plasmas. A key requirement is a high degree of control over the composition, power, and energy of the plasma so that small but measureable amounts of damage can be produced and in turn compared to ablation rates predicted by first-principles computation using molecular dynamics (MD) simulations. This paper describes the design and performance of a non-consumable capillary discharge that uses a quartz liner, to produce a 1 eV argon plasma. The argon feed-gas contains 2% hydrogen for permitting additional spectroscopic diagnostics of the plasma. Measurements of plasma temperature, plasma density, and power are provided for various configurations of the power supply and capillary which was operated at 4 kV, and which used a flash lamp type circuit for initiating the discharge.