Speaker
Seo Jin Jeong
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1022.pdf
Experimental study of sheath heat transmission factors by thermocouples
and triple probe in DiPS-2
S.J. Jeong1, M.-K. Bae1, I.J. Kang1, H.T. Oh1, I.S. Park1, S.H. Lee1, K.-S. Chung1
1
Department of Electrical Engineering, Hanyang University, Seoul, South of Korea
Accurate prediction of heat flux is important because the lifetime of fusion reactor could be
determined by the damage of various PFC’s due to the high heat flux. The measurement of heat
flux relies on determination of sheath heat transmission factor ( 𝛾𝑠 ). Besides infrared
measurement, thermocouple have provided reliable data for heat flux measurements [1, 2].
Plasma was generated in a linear device, called Divertor Plasma Simulator-2 (DiPS-2), with the
following conditions: plasma density (ne) ~ 1017 cm-3 and electron temperature (Te) ~ 1 - 15 eV
with argon, where plasma is flowing into a chamber, called DiSC (Dust interaction with
Surfaces Chamber). Thermocouples and a triple probe were used to measure the heat flux
toward the tungsten target in DiSC, which was operated with discharge current = 10 – 40 A,
plasma density (ne) ~ 1016 – 1017 cm-3 and electron temperature (Te) ~ 1 – 15 eV. Based upon a
simple sheath theory, a theoretical sheath heat transmission coefficient can be estimated as
approximately 6-7 in pure argon plasma [3, 4]. To deduce the sheath heat transmission factor
experimentally, three thermocouples were embedded directly into the tungsten target with
thickness of 20 mm. Each thermocouple is located at 18 mm, 13 mm, and 3 mm from target
surface, respectively. Theoretical heat flux estimated at DiSC center is about 30.76 kW/m2.
Heat flux have been deduced by thermocouples in utilizing a simple heat conduction equation,
𝑞𝑇𝐶 = −𝑘(𝑇1 − 𝑇0 )/(𝑥1 − 𝑥0 ) , where T, 𝑥 are thermocouple temperature and position of
thermocouple. Triple probe measured the electron temperature and ion saturation current. From
these measurements, sheath heat transmission factor is obtained from 𝛾𝑠 = 𝑞𝑇𝐶 ⁄𝑘𝑇𝑒 Γ .
Experimental values of sheath heat transmission factors in argon plasma have been compared
with theoretical values. To expand the case of pure plasma to the impure plasma, we have
generated He + Ar/N2 plasmas. By varying the pressure ratio of additional gas (Ar, N2), effect
of impurity in sheath heat transmission factor was also investigated.
[1] H. Matssura et al, Contrib. Plasma Phys. 54 (2014) 285.
[2] D. Donovan et al, J. Nucl. Mater. 438 (2013) S467.
[3] S. Marsen et al, J. Nucl. Mater. 438 (2013) S393.
[4] J. Marki et al, J. Nucl. Mater. 363 (2007) 382.
