BOOK OF ABSTRACTS 2012 International - Ness Engineering, Inc.

INITIATION MECHANISM OF NEGATIVE PULSED DISCHARGE IN
SUPERCRITICAL CARBON DIOXIDE
Tomohiro Furusato, Takeshi Ihara, Tsuyoshi Kiyan, Sunao Katsuki, Masanori
Hara, Hidenori Akiyama
Kumamoto University, Graduate School of Science and Technology, Kumamoto, Japan
11
2O3
The initiation mechanism of an electrical discharge in high density mediums is complex and has
been the subject of extensive research for many years. Studies have shown that the initiation
process is associated with the chemical composition and physical properties of the dielectric
medium, the medium state, electric field distribution, and the waveform of the applied voltage,
and that it involves very complex phenomena. Current theories of the discharge initiation
mechanism in non-uniform field gaps in high density medium can be divided into two categories:
(1) the so-called bubble triggered ionization mechanism; and (2) the direct ionization model. In
our preceding study [1], results were presented of positive streamer initiation mechanism in a
point-to-plane gap in compressed CO2 under ns pulsed voltage by using Schlieren and
photomultiplier techniques. The results showed that direct ionization by free electrons is the
dominant mechanism in positive streamer initiation. In the present study, the initiation process of
an electrical discharge in a negative point-to-plane gap in supercritical phase was investigated
experimentally with the same experimental setup, measurement, and observation techniques as
the previous study. Experimental results show that the structure and process of a negative
discharge at the initial stage are strikingly different from that of the positive one.
[1] T. Ihara, T. Furusato, S. Kameda, T. Kiyan, S. Katsuki, M. Hara and H. Akiyama, "Initiation
Mechanism of Positive Streamer in Pressurized Carbon Dioxide up to Liquid and Supercritical
Phases with Nanosecond Pulsed Voltages", J. Phys. D: Appl. Phys. (in Press)