Self-breakdown statistics of a high-pressure spark gap with a microarray graphite cathode

Abstract

Comparative measurements with high-pressure spark gaps (gas pressure: 0.2–0.9 MPa nitrogen, gap spacing 5 mm) are presented, one with a regular Bruce-profile polished graphite cathode (diameter 25 mm, thickness 8 mm) and the other with a microarray graphite cathode of equal dimensions. By microstructuring, a V-type graphite microarray is created by purpose-developed laser treatment of a plane graphite electrode. The microarray graphite cathode brings more initial plasma and then produces more initial electrons. It is beneficial for electron emission, which improves the stability of the switch breakdown. The experimental results are achieved at a gas pressure of 0.9 MPa and a 200-kV voltage pulse applied to the switch. With these parameters, the mean breakdown voltage is 91.7 kV, the minimum is 91.4 kV, and the mean relative standard deviation in breakdown voltage of the first 100 shots is 0.4%. Compared to a plane graphite cathode, the mean breakdown voltage is about 10% lower, and the mean relative standard deviation is reduced by more than 90%. The main result can be stated that microarray graphite cathodes are a suitable choice as electrodes for low-jitter high-pressure spark gaps.

Full text

Review of
Scientific Instruments ARTICLE pubs.aip.org/aip/rsi
Self-breakdown statistics of a high-pressure spark
gap with a microarray graphite cathode
Cite as: Rev. Sci. Instrum. 95, 074712 (2024); doi: 10.1063/5.0202398
Submitted: 4 February 2024 •Accepted: 8 July 2024 •
Published Online: 24 July 2024
Gang Wang, Jiancang Su, Wenyuan Liu, Sheng Liu, Yankun Huo, Yafeng Pan, Hongyan Fan,
and Shifei Liua)
AFFILIATIONS
Northwest Institute of Nuclear Technology, P.O. Box 69 Branch 13, Xi’an 710024, China
a)Author to whom correspondence should be addressed: gfkdlsf@163.com
ABSTRACT
Comparative measurements with high-pressure spark gaps (gas pressure: 0.2–0.9 MPa nitrogen, gap spacing 5 mm) are presented, one with a
regular Bruce-profile polished graphite cathode (diameter 25 mm, thickness 8 mm) and the other with a microarray graphite cathode of equal
dimensions. By microstructuring, a V-type graphite microarray is created by purpose-developed laser treatment of a plane graphite electrode.
The microarray graphite cathode brings more initial plasma and then produces more initial electrons. It is beneficial for electron emission,
which improves the stability of the switch breakdown. The experimental results are achieved at a gas pressure of 0.9 MPa and a 200-kV voltage
pulse applied to the switch. With these parameters, the mean breakdown voltage is 91.7 kV, the minimum is 91.4 kV, and the mean relative
standard deviation in breakdown voltage of the first 100 shots is 0.4%. Compared to a plane graphite cathode, the mean breakdown voltage
is about 10% lower, and the mean relative standard deviation is reduced by more than 90%. The main result can be stated that microarray
graphite cathodes are a suitable choice as electrodes for low-jitter high-pressure spark gaps.
Published under an exclusive license by AIP Publishing. https://doi.org/10.1063/5.0202398
I. INTRODUCTION
A spark gap switch is widely used in many pulsed-power
devices and high-voltage systems. Spark gap switches with low rel-
ative standard deviation (RSD) of the breakdown voltage and long
lifetime are becoming a research hotspot internationally.1–4 Recent
investigations of decreasing the RSD of self-breakdown voltage have
been undertaken, including optimizing electrode materials, electric
field distribution, and surface morphology.5–7
The influence of electrode materials on the static performance
of spark gap switch was studied, including stainless steel, brass,
tungsten-copper alloy, and graphite.5The experimental results show
that the RSD of the breakdown voltage of gas switches using graphite
electrodes is much lower than that with other electrode materi-
als. It is believed that the surface roughness of discharged graphite
electrodes is lower than that of other metal electrodes because the
sublimation temperature is high and most of the ablation production
for graphite electrodes is gas.
The stability of a 2-MV pulse gas switch was found to be influ-
enced by the shape of the switch electrodes.6According to the
breakdown mark on the smooth electrode, the breakdown char-
acteristic of the switch could be made more stable by making a
slot in one electrode. The initial electronics can be easier to build
by the partial field enhancement between electrodes, which will
improve the breakdown stability of the pulse gas switch.
A field distortion switch with carbon fiber and metal matrix
composite electrodes was developed.7Carbon fiber material has
a high melting point and strong ablation resistance, so the elec-
trodes using this material can conduct large currents. In addition,
the microstructure of carbon fiber with a high aspect ratio can
produce a high partial field enhancement, which can also obtain uni-
form distribution and sufficient concentration of initial electrons.
The experimental results show that the switch structure is in good
agreement and the breakdown characteristics of the switch are very
stable.
The microarray structure is also widely used in the aspects
of insulation materials. The surface flashover characteristics of
microstructure on the insulators were studied.8–10 The results
show that the microstructure can suppress secondary electron
multiplication and increase the flashover voltage.
According to the above research, combining the advantages of
graphite materials and multi-tip array structures on electron emis-
sion stability, a design and fine construction of microscopic features
on the surface of graphite is conducted. A self-breakdown spark
Rev. Sci. Instrum. 95, 074712 (2024); doi: 10.1063/5.0202398 95, 074712-1
Published under an exclusive license by AIP Publishing