24B01
Theoretical analysis on reaction process of active species in atmosphericpressure streamer discharge
シミュレーションによる大気圧ストリーマ放電の活性種生成機構解明
Atsushi Komuro, Ryo Ono, and Tetsuji Oda
1
小室 淳史, 1小野 亮，2小田 哲治
1

1

Advanced Energy, The University of Tokyo. 2Electrical engineering, The University of Tokyo.
5-1-5 Kashiwanoha, Kashiwa, Chiba, 227-8568, Japan. 27-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
1〒227-8658 千葉県柏市柏の葉5-1-5，2〒113-8656 東京都文京区本郷7-3-1
A practical streamer discharge model is developed to analyze the characteristic of pulsed streamerdischarge in a positive point-to-plane electrodes filled with air at room temperature and atmosphericpressure. The calculated primary and secondary streamer development shows good agreement with anexperimentally obtained streak photograph. The experimentally obtained axial distribution of oxygen andnitrogen radical productions by streamer discharge can be successfully reproduced in our simulation

1. Introduction
Streamer like discharges is widely used in many
applications such as decomposition of gaseous
pollutant, water treatment, ozone production,
surface treatment and medical application.
However, the understanding of the phenomena isstill poor. The complete simulation of thestreamer discharge can lead to a better
understanding of the physico-chemical activity
and help us to choose the best operating
conditions (such as reactor geometry, the flue gas
resident time, the applied voltage shape andmagnitude) in order to improve the process
efficiency. To perform quantitative analysis of
the efficiency of various applications, an insightis needed into the physics of streamer propagation
processes. For one of the important factors instreamer discharge phenomenon, it is known thatthe vibrationally excited molecules have large
influence on the discharge phenomenon.
2. Kinetic model
The propagation of a streamer discharge isconsidered in a point to plane electrodeconfiguration with a gap distance of 13mm. In order
to simulate the discharge development, we chose acylinder domain of 18cm height and 8.0cm radius.
The total number of grid is Nz×Nr = 1972×256
with spatial steps from dz = 1 m (near point andplane) to 10 m (inter-electrode gap) for z-axis andfrom dr = 2.5 m up to 200 m for r-axis. Thepoint electrode has a revolutionary hyperboloid
shape with a radius of 40m. The simulation
conditions are summarized in Table.1.
To compute the streamer propagation in air, we
use first-order electro-hydrodynamic model forelectrons, positive and negative ions in theframework of the drift-diffusion approximation.

Table.1. Simulation condition

Temperature
Pressure
Gas components
Gap length
Point curvature radiusTime step
Initial electron density

300 K
101 kPa
Dry Air
13 mm
40 mm
2.5×10-13 s
103cm-3Thus, the equations involved in this model arefollowingn(r , t )   r [n(r , t )v(r , t )]  S (r , t ) (1)t 2 1   2q 2  (n p  ne  nn ) (2)2r r z0
rwhere, n(r,t) is the charged particle density，S(r,t)
is the particle chemical source term, v(r,t) is theparticle velocity， is electric potential，0 is thepermittivity of free space，q is the absolute value ofthe electronic charge. The subscripts of e, p and nstand for electron, positive and negative ions,respectively. The transport and source parameters(such as particle mobilities and reaction
coefficients) are calculated using Bolsig+ [1] withpublished e-V cross sections [2].
Photoionization is taken into account through thethree-exponential Helmholtz models derived by
Luque et al. [3]. The charged species transport
equations are solved with the MUSCL superbee
algorithm. To solve the Poisson's equations andphotoionization term, we use Red&Black Multigrid
method and calculate it on GPU (Graphics
Processing Unit). Due to this powerful GPU
computing method, the performance of solving

Figure.2. Axial
distribution of oxygen radical
radicalFigure.2.
Axial distribution
density at t = 100
100 nsns andand streamer
streamer luminous
luminous
densityintensity for
intensity
forVV==32,32,24
24andand1616kV.
kV.

already obtained from out experimental results [5].
For N radical production, it is generally
considered that N radicals are produced byfollowing reactions [6]
N 2 (X1 g )  e  N *2  eFigure.1. Two(a) (a)reducedelectric
field
Figure.1.
Twodimensional
dimensional
reducedelectric-3
E/NTd)
electrondensitydensity(in cm-3) forfield(inE/N(inandTd)(b)and(b) electron(incm13)mmgapmmdischargeat time tat= time
20 ns.t = 20 ns.
for 13gap discharge

Poisson's equation achieves 40 times speed upcompared with 1 core CPU calculation.
3. Results
Figures.1 shows the 2-D structure of the absolutevalue of the reduced electric field and the electron
density for 13 mm gap point to plane discharge.
Figure.1(a) indicates that the streamer headpropagates with a high electric field toward thecathode and streamer channel corresponds to ahighly conductive channel connecting the streamer
head to the anode. The reduced electric field isequal to 20 Td in the streamer channel and around
800 Td in the streamer head. Figure.1(b) shows thatthe electron density in the streamer channel ishigher than 1014cm-3. From both figures, thestreamer channel radius, which is defined as theradial extension of low reduced electric field area inthe streamer channel, is estimated at 300 m andthe mean streamer velocity is around 4.3×105
m/s. These results show good agreement with ourexperimental results [4].
Figures.2 show the axial distribution of O radicaldensities at t = 100 ns and streamer luminous
intensities for V = 32, 24 and 16 kV. In figures.2,
the axial distribution of oxygen radical densities
and streamer luminous intensities are roughly ingood agreement. This characteristic has been N(S)  N(D)  e
N *2  (sum of thesingret states)
However, these reactions alone cannot explain therelatively high dissociation degrees observed
experimentally [7]. Therefore, many otherprocesses for nitrogen dissociation have beensuggested. The following mechanism is known as
one of these processes [8]N 2 (X1 g , v)  e  N 2 (B3 g , v'  12)  e

N 2 (a1 g , v'  6)  e
 N(S) N(S, D) e
These reactions closely related to thevibrationally excited molecules of nitrogen and are
efficient in low energy region. We can successfullyreproduce our experimental data by these processes.
In atmospheric pressure streamer discharge,
vibrationally excited molecules have great influenceon the production of N radicals.
References[1] Hagelaar G et al., Plasma Sources Sci. Technol., 14,722.
[2] PHELPS database, www.lxcat.laplace.univ-tlse.fr[3] Luque A et al., Appl. Phys. Lett., 90, 081501[4] Ono R et al., J. Phys. D: Appl. Phys., 36, 1952[5] Ono R et al., J. Appl. Phys., 106, 043302[6] Popov NA et al., J. Phys. D: Appl. Phys., 44, 285201[7] Guerra V et al., Eur. Phys. J. Appl. Phys., 28, 125[8] Cacciatore M et al., Chem. Phys., 66, 141