This thesis presents the experimental and theoretical studies of nonthermal and
stable atmospheric-pressure glow discharges. With the excitation frequency in the
kilohertz range, a uniform and stable glow discharge has been successfully produced
in atmospheric helium without the usually indispensable dielectric barrier. For this
barrier-free cold atmospheric discharge, there are two discharge events occurring,
respectively, in the voltage-rising and the voltage-falling phases, and in general they
compete with each other. This distinct feature is illustrated through a detailed fluid
simulation. For direct current atmospheric glow discharges, their cathode fall region
is shown to depend critically on the discharge current density. For atmospheric glow
discharges excited at 13.56 MHz on the other hand, we present observations that
after gas breakdown, the discharge evolves from the normal glow mode to the
abnormal glow mode and then through the recovery mode back to the normal glow
mode. The operation modes, namely the a mode and the y mode, in radio-frequency
atmospheric glow discharges are investigated with a one-dimensional, self-consistent
continuum model. This model is evaluated by comparing our numerical results with
experimental data and other simulation results in literature. It is shown that gas
ionization is volumetric in the a mode and localized in the boundary region between
the sheath and the bulk plasma in the y mode. The stable operation regime in the a
mode is found to have a positive differential conductivity, and can be expanded to
higher discharge current density without compensating plasma reactivity by
increasing the excitation frequency. Furthermore this plasma stability-reactivity
balance is also studied for radio-frequency atmospheric glow microdischarges.
History
School
Mechanical, Electrical and Manufacturing Engineering