Effects of Frequency on the Electrical Characteristic of Pulse Discharges in Atmospheric-Pressure Pure Helium

The effects of the frequency on the electrical characteristics in a dielectric barrier discharge in pure helium excited by repetitive voltage pulses with the frequency
f
from 5 to 500 kHz are systematically investigated by means of a 1-D fluid model under different operating conditions, including gap width
dg
, secondary electron emission coefficient γ, dielectric thickness
ds
, and dielectric constant ε
r
. The important characteristic quantities of describing the pulse discharge, i.e., discharge current density
Jg
, averaged electron density
N
_ave
, averaged dissipated power density
P
_ave
, and the axial distributions of both electron density
Ne
and electron temperature
Te
, are calculated and analyzed in detail. This paper gives the following significant results.
N
_ave
increases with increasing
f
and
P
_ave
is almost proportional to
f
. Especially, there is a characteristic frequency of ~ 50 kHz, namely, when
f
is lower than ~ 50 kHz,
Jm
1 (peak value of
Jg
in the first discharge) decreases evidently with increasing
f
, and then changes very slightly for
f
s larger than ~ 50 kHz. In addition, with the increase of
f
,
Jm
2 (peak value of
Jg
in the second discharge) increases very slightly for small
ds
and the reverse is true for large
ds
. The frequency dependence of
Jm
2 for different ε
rs
is similar to that by changing
ds
. For a fixed frequency, the change of
Jm
1 with γ is very small, which differs from that at low frequencies. In addition,
Jm
1 and
Jm
2 decrease with increasing
ds
and increase with increasing ε
r
, but there are almost constant Δ
Jm
1 and Δ
Jm
2 for high frequencies. When the frequency is larger than ~ 50 kHz, there will be the second peak of
Ne
outside the cathode sheath in the first discharge, and both large
ds
and small ε
r
can result in the formation of the evident peak of
Ne
nearby the momentary anode. It should be noted that the analysis in this paper pertains only to the incompressible motion of the plasma.