Speaker
In Je Kang
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1033.pdf
Generation of supersonic plasma flow in DiPS-2
I.J. Kang, M.-K. Bae, I.S. Park, S.H. Lee, S.J. Jeong, K.-S. Chung,
Department of Electrical Engineering, Hanyang University, Seoul, South of Korea
Flow measurements near X-points including E × B shear velocity and supersonic flow are
still under debate [1, 2] in fusion devices, although the progress of edge plasma physics has
been advanced in recent years. Various kinetic and fluid models have been developed on plasma
flow phenomena at fields of fusion plasmas. However, subsonic plasma flow has been mostly
studied for verification of models, which requires further verification for supersonic plasmas.
Also, the generation and measurements of supersonic plasma flow have been studied at pulsed
plasma system or transient phenomena, which are still insufficient in steady state plasma
conditions, even.
In this experiments, a concept of ion extraction system [3] has been adopted to generate
supersonic plasma flows (M∞ > 1) at weakly magnetized plasma in steady state condition. A
cylindrical ion extraction electrode of stainless steel, which has a diameter = 5 cm and an axial
length = 4 cm, was used. In test for generation of supersonic plasma flow, the first result on the
ion velocity distribution with supersonic plasma flow ( M∞ = ~ 1.2) was obtained in a
capacitively coupled plasma with electron temperature (Te) ~ 2 eV and plasma density (ne) ~
1010 cm-3 by using Mach probe.
Ion extraction system was applied to a linear plasma device called DiPS-2 (Divertor Plasma
Simulator - 2: length = 3560 cm, diameter = 20 cm, source = LaB6 cathode, average density ~
1011 - 1013 cm-3, Te ~ 1 - 20 eV for Ar plasmas) [4]. To analyze drift velocity in supersonic
plasma flow in terms of discharge currents and biased voltages to ion extraction electrode, a
laser induced fluorescence (LIF) system was adopted with measurement of Mach probe. The
LIF system composes of a tunable diode laser with a master oscillator power amplifier (MOPA),
which has typical ouput power = 10 - 100 mW, line width = 1 MHz, coarse tuning range = 665
- 675 nm with a rotating grating, fine tuning range = 0.45 nm with piezo-electric actuator control
from 0 to 100 Volt, and a mode-hop free tuning region > 16 GHz, with current coupling method,
to pump Ar II transition 3d4F7/2 metastable level to the 4p4D5/2 level at 668.43 nm. The 442.60
nm fluorescence light emitted from 4p4D5/2 level to 4s4P3/2 level was collected to determine drift
velocity in supersonic plasma flow. For validity of experimental results on supersonic plasma
flow, LIF data was compared with Mach probe results with various calibration factors
introduced from Mach probe theory.
[1] Y. Nishimura et al., Contrib. Plasma Phys. 44 (2004) 194.
[2] N. Asakura et al., J. Nucl. Mater. 363 (2007) 41.
[3] Y. Nambu, J. Plasma Fusion Res. SERIES 8 (2009) 920.
[4] I. J. Kang et al., Curr. Appl. Phys. 17 (2017) 358.
