Soon-Gook Cho

Analysis of Electron Temperature in DC Ar/SF6 Plasma Using Cylindrical and Planar Probes

Electronegative plasmas are generated by adding SF6 gas to a background argon (Ar) DC plasma with parameters of n0 = 1×1010 cm3 and Te = 2 eV. The heating current of the thoriated filament was in the range of 20.5–21.5 A and the plasmas were generated under a discharge condition of 100 V/0.4 A. The amount of negative ions was controlled by adjusting the ratio of flow rate of SF6 = 0–10% to that of Ar. Plasma parameters were measured using cylindrical and planar electric probes. The behavior of electrons, which means the change in a parameter due to negative ion production, is characterized by measuring the floating and plasma potentials, and electron temperature. Electron temperature seems to increase and the potentials decrease with SF6 flow rate.

Plasma-Wall Interaction Facilities in Korea

Although the research of plasma-material interaction (PMI) is rather immature comparing the recent success of Korean fusion program, there are several facilities and programs of PMI research in Korea. DiPS (Divertor Plasma Simulator)-2 is a linear device with a four-inch-LaB6 cathode at the Center for Edge Plasma Science (cEps), concentrating on the development of various diagnostics for divertor and scrape-off plasmas, and for PMI research such as tungsten and graphite related phenomena. This is modified from DiPS-1, which were for the simulations of divertor, space and processing plasmas using LaB6 and helicon plasma sources. MP2 (Multi-Purpose Plasma) is a linear device with an eight-inch-LaB6 cathode for PMI in National Fusion Research Institute (NFRI), and will be merged with molten salt (FLiNaK) experiment by using an Electron Cyclotron Resonance (ECR) plasma source. High power plasma torch facilities have been developed at the High-Enthalpy Plasma Research Center in ChonBuk National University, aiming for the development of new materials of the aerospace-, nano-, and automobile-industries, yet recently they have interest in fusion materials. Plasma Immersion Ion Implantation & Deposition (PIIID) facility has been utilized for the research of processing materials in Korean Institute of Science and Technology (KIST), and is to be used for fusion material researches with high energy ions (~70 keV). Electron beam irradiation has been tried for the research of graphite and tungsten at DanKook university. These facilities are to be utilized for the application to KSTAR, ITER and/or Korean DEMO fusion devices. Dust as the by-product of PMI in fusion device is to be characterized and removed in TReD (Transport & Removal experiment of Dust) device in Hanyang University. Plasma sources, diagnostics, and surface analyses of these programs will be explained with design philosophies and basic parameters of plasmas.

Development of a Laser Induced Fluorescence (LIF) system on the Plasma Material Interaction System (PLAMIS-II) device

A laser induced fluorescence (LIF) system has been developed for the plasma material interaction system (PLAMIS-II) device, which is equipped with a unique plasma gun composed of a LaB6 cathode and two anodes with electromagnets to generate a focused dense plasma. PLAMIS-II simulates the interactions of plasma with different materials and is to be used for the test of plasma facing components of fusion devices. The LIF system is composed of a seed laser with Littmann/Metcalf cavity and a master oscillator power amplifier to pump 3d4F7/2 metastable argon ion to 4p4D5/2 level at the wavelength of 668.61 nm, which has the following input parameters: laser power = 20 mW, line width 70 GHz. For in-situ measurement of laser wavelength, the wavelength spectrum of an iodine cell was measured by a photo-transistor during LIF measurement. To measure argon ion temperature (Ti) and drift velocity (vd) in PLAMIS-II, the fluorescence light with the wavelength of 442.72 nm, emitted from 4p4D5/2 level to 4s4P3/2 level and passing through 1 nm band-width filter, was collected by the photomultiplier tube combined with a lock-in amplifier and a chopper with frequency of 3 kHz. Initial data of Ti and vd were analysed in terms of gas flow rate and applied power.

Measurement of Negatively Charged Dust by Using an Electric Probe in Large RF Helium Plasmas

Abstract We investigated charged dust and its effect on RF plasma by using a planar electric probe in a large-scale device. In background plasmas, the particle density is 108 to 109 cm−3 and the electron temperature is 2 to 4 eV. When dust is contained in plasma, it is negatively charged by electrons attached to the dust. The charged dust density and the charge were calculated by comparing dusty helium plasma to pure helium plasma. Depending on the increase in the amount of dust, the charged dust density increases with the decrease in the charge due to depletion of the electrons in the background plasma. The results show that the charge changes the interactions between the dust and particles in the background plasma.