28pC09
Studies of Pulsed Filament Discharges Using Laser Thomson Scattering
Diagnostics
Nima Bolouki, Kentaro Tomita, Yukihiko Yamagata, Kiichiro UchinoInterdisciplinary Graduate School of Engineering Sciences, Kyushu University

Non-thermal plasmas produced at atmosphericpressure have been paid much attention for theirgreat possibility to expand application fields ofplasmas, such as plasma nano science, plasma
biomedicine, and plasma chemistry. We present anexperimental study in non-thermal plasmas andstreamer phase at around atmospheric pressure.
Generally, such plasmas occur in the form of very
rapid pulse in order of nano second. So, the direct
measurement of electron density and electron
temperature are very difficult. In order to measuresuch plasmas parameters, we have been developing
laser Thomson scattering (LTS) as a diagnosticsystem. Figure 1 shows the experimental setup of
LTS system. The light source of LTS is the second
harmonics Nd:YAG laser having a wavelength of532nm, a repetition rate 10 Hz, and a pulse width of
6 ns which is injected in pulsed filament discharge.
The laser is controlled using an external trigger tosynchronize the laser timing with the discharge.
Also a triple grating spectrometer (TGS) having
high rejection rate is used to measure LTS spectra.
Finally, the scattered spectrums are detected by an
ICCD camera (Princeton, PI-MAX UNIGENII). In
order to observe a clear spectrum, the signals areaveraged over a number of 2000 shots. As a plasma
source, we have selected capacity coupleddischarge (CCD) and dielectric barrier discharge(DBD) separately, which are a type of thenon-thermal plasma. The pulsed filamentary
discharge in both plasma sources are generated inneon gas at a pressure of 400 Torr by applying therepetitive voltage pulses at a frequency of 10 Hz
with a peak value of 3.0 kV. The electrode set isconsisted of a needle electrode and a hemisphericalelectrode with a gap of 0.5 mm. Moreover, in DBD
micro plasma, Teflon as a dielectric layer is coatedon the hemispherical electrode. In this study, wemeasured temporal evolution of electron densityand electron temperature as well as spatiotemporal

evolution. In both plasma sources, the value ofelectron density remains almost constant for thefirst 30 ns, and then decreases monotonously. On
the other hand, the electron temperature is 1.5 eV ormore for the early time, then decreases rapidly
down to about 0.8 eV at 50 ns by the elastic
collision with the neutral particle and the ion. The
error ranges for these values were estimated to beabout ± 15%. Also the total electric charges thatflow through the discharge channel vary from 20nC to 800 nC by changing the capacitance inelectrical circuit. We could show that the totalcharge variation leads to increase in electron
density from 1022 m-3 to 1023 m-3. However, theelectron temperature remains almost constant at themain discharge. In order to investigate the streamer
phase, we changed the gap up to 16mm. thebeginning of the discharge was controlled well intime and position. Then the LTS method wasperformed to measure the same procedures which
we had done in non-thermal discharge.

Triple Grating Spectrometer
ICCD Camera

Electrode Set

f=250 mm
f=120 mm
Beam Dump

Nd:YAGLaser
f=200 mmElectricCircuit

DelayGenerator

Fig. 1 Schematic illustration of laser Thomson scattering setup