22P171-B
Transition processes of recombining plasma with pulse plasma flow
パルスプラズマ流入時における再結合プラズマの遷移過程
Takaaki Iijima, Naoki Mine, Akira Tonegawa, Kazutaka Kawamura and Kohnosuke Sato
飯島貴朗, 嶺直樹，利根川昭，河村和孝, 佐藤浩之助
Department of Physics, School of Science, Tokai University
411 Kitakaname, Hiratsuka, Kanagawa, 259-1292, Japan
東海大学 〒259-1292 神奈川県平塚市北金目411

The time evolution of electron density ne, electron temperature Te, electron velocity distribution function
ƒe()and hydrogen Balmer series spectra is found to depend on gas pressure in the recombination plasma
with pulse plasma flow. The pulse plasma flux is generated by controlling the electric circuits ofelectrodes of plasma source. The negative spikes were appeared in the time evolution of the Balmer
series spectra, which indicate on the transition from ionizing to recombining plasma.

1. Introduction
The research on the dynamic behaviors of plasma
against the pulse plasma flow with bursts of heat andparticles is a topic in space plasma, and fusion relatededge
plasmaphysics.
In
particular,
thetime-dependence of recombination processes with pulse
plasma flow has become important for characteristics ofplasma detachment, in which the transitions fromrecombination to ionization plasma have been identified
in divertor region of fusion device.
The transient behavior of the recombination plasma
with pulse plasma flow has been studied by observing
the short double minimum (negative) spike in Demission from the plasma[1]. This response in Demission is explained by the electron temperature
increase associated with pulse plasma flow with bursts ofheat and particles along the magnetic field. However, it
is required that experiments which will aid theunderstanding of the role of the high energy electronwith pulse plasma flow are carried out.
In this study, we have carried out the experimental
observation of the time evolution of electron density ne,electron temperature Te, electron velocity distributionfunction ƒe()and hydrogen Balmer series spectra inhydrogen recombination plasma in a liner plasma device,
TPD-SheetIV[2].

2. Experimental Apparatus and Method
Figure 1 show the schematic view of the TPD-SheetIV
device and measuring system[2].
The plasma in
TPD-SheetIV was divided into two regions: the sheet
plasma source region and the experimental region.
TTen rectangular magnetic coils formed a uniform
magnetic field of 0.8 kG in the experimental region. The
hydrogen plasma was generated at a hydrogen gas flowof 75 sccm, with a discharge current of 30-100 A. The
neutral pressure P in the experimental region was

Target plate
Langmuir probe

Magnetic field
Water coolingPlasmaLends
Gas feeder

Fig.1 Schematic view of the TPD-SheetIV device
and measuring system.
controlled between 0.01 and 2.0 Pa with a secondary gas
feed. Electron density and electron temperature were
measured using a planar Langmuir probe and double
probe, which were located 3 cm in front of the obliqueendplate.
The recombination plasma with pulse plasma flow wasgenerated by controlling the electric potential of the next
floating electrode of the anode in TPD-type plasma
source. Pulse plasma flow generated by controlling theplasma source were introduced into hydrogen
recombination plasma in the experimental region. The
duration of the pulse plasma was 0.3ms and thefrequency of cycle of the plasma was 50Hz.
The time
evolution of the emission intensity of the Balmer series
spectra was observed with a spectroscope and aphotomultiplier. The time evolution of electron density
ne, electron temperature Te, electron velocity distributionfunction ƒe() and hydrogen Balmer series spectra inhydrogen recombination plasma were measured using
Langmuir probe, which were located 3cm in front of theendplate.
3. Experimental results
Figure 2 shows the typical time evolution of theelectron temperature Te and electron density ne at aneutral gas pressure of 1.1 Pa (recombination plasma).
The discharge current is 70 A in hydrogen plasma.
Both Te and ne increase and peak after the pulse plasma
flow is introduced. Figure 3 shows the time evolutionof the electron velocity distribution function ƒe()at aneutral gas pressure of 1.1 Pa. ƒe()were obtained byderivative of the probe Ip-Vp curve. It is found that thehigh energy electrons around 40 eV appear inrecombination plasma after the pulse plasma flow isintroduced. Figure 4 shows the typical time evolutionof the line emission intensities of H and Hε at aneutral gas pressure of 0.3 1.0 Pa. The H emission

intensity in recombination plasma is found to drop intime, indicating that recombination becomes weak.
After the appearance of double minimum negative spikes
at around 0.5 ms, the emission intensity starts to increase
gradually. The ionization and recombination events are

discussed by Collisional-Radiative (CR) model, taking
into account of high energy electrons as shown in
Fig.5. It is indicated that the recombination plasma
decay for increase of ionization plasma during thepulse plasma flow.
4. Conclusions
The time evolution of electron density ne, electron
temperature Te, electron velocity distribution function
ƒe(), and hydrogen Balmer series spectra is found todepend on gas pressure in the recombination plasma withpulse plasma flow. The high energy electrons in thepulse plasma flow are influenced by the time evolutionof the Balmer series spectra, which indicate on thetransition from ionizing to recombining plasma.
References[1] N.Ohno, et al. ,Nucl. Fusion 41(2001)1055.

[2] A.Tonegawa, J.Nucl.Mater.,313-316 (2003)1046.
Hα emission intensity[×1013 phm-3 s-1]

4.5
4.0
3.5
3.0
2.5
3.5
3.0
2.5
2.0
1.5

-0.5

0.0

0.5

1.01.5Time [ms]

1.8

Hα

1.6
1.4
1.2
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2

Hε-0.5

0.0

0.5

1.0

1.5

Time [ms]Fig.4 typical time evolution of the line emission
intensities of H and Hε at a neutral gas pressureof 0.3 1.0 Pa.

Recombination events[×1013]ionization events[×1014]

Fig.2 Typical tiame ebolution of the electron
temperature and electron densityat a neutral
gas pressure of 1.1 Pa.

Hε emission intensity[ ×10 11 phm-3 s-1 ]Electron temperature Electron density
Te [eV]Ne [1018 m-3]

intensity increase and peak after the pulse plasma flow

is introduced. On the other hand, the Hv5 emission

1.8
1.6
1.4
1.2
1.0
4.2
4.0
3.8
3.6
3.4
3.2
3.0
-0.5

0.0

0.5

1.0

1.5

Time [ms]Fig.3 the time evolution of the electron velocity
distribution function ƒe()at a neutral gas pressureof 1.0 Pa.

Fig.5

The ionization and recombination eventsare discussed by CR model, taking into account ofhigh energy electrons.