Kyoung-Jae Chung

A new spherical torus called VEST (Versatile Experiment Spherical Torus) is designed, constructed and successfully commissioned at Seoul National University. A unique design feature of the VEST is two partial solenoid coils installed at both vertical ends of a center stack, which can provide sufficient magnetic fluxes to initiate tokamak plasmas while keeping a low aspect ratio configuration in the central region. According to initial double null merging start-up scenario using the partial solen

This paper presents a simple but quite accurate numerical model for analyzing electrical explosion of copper wires in water. The numerical model solves a circuit equation coupled with one-dimensional magneto-hydrodynamic (MHD) equations with the help of appropriate wide-range equation of state (EOS) and electrical conductivity for copper. The MHD equations are formulated in a Lagrangian form to identify the interface between the wire and surrounding water clearly. A quotidian EOS (QEOS) that is

Thermodynamics of a magnetically expanding plasma (magnetic nozzle (MN)) has been investigated considering the existence of confined electrons bouncing back and forth inside a potential well formed by a combination of external magnetic field and self-generating ambipolar electrostatic potential. The properties of confined electrons are distinguished from that of the adiabatically expanding electrons with gamma(e) approximate to 5/3 by the separate measurement of each species using a double-sided

In order to describe the Bauschinger and transient behavior of orthotropic fiber-reinforced composite solids, a combined isotropic-kinematic hardening law based on the non-linear kinematic hardening rule was considered here, in particular, based on the Chaboche type law. In this modified constitutive law, the anisotropic evolution of the back-stress was properly accounted for. Also, to represent the orthotropy of composite materials, Hill's 1948 quadratic yield function and the orthotropic elast

In a volume-produced negative hydrogen ion source, control of electron temperature is essential due to its close correlation with the generation of highly vibrationally excited hydrogen molecules in the heating region as well as the generation of negative hydrogen ions by dissociative attachment in the extraction region. In this study, geometric effects of the cylindrical discharge chamber on negative ion generation via electron temperature changes are investigated in two discharge chambers with

This paper presents a method for enhancement of shock waves generated from underwater pulsed spark discharges with negative (anode-directed) subsonic streamers, for which the pre-breakdown process is accelerated by preconditioning a gap with water electrolysis. Hydrogen microbubbles are produced at the cathode by the electrolysis and move towards the anode during the preconditioning phase. The numbers and spatial distributions of the microbubbles vary with the amplitude and duration of each prec

Abstract Composition, thermodynamic properties, and electrical conductivity of water plasma are calculated under the assumption of thermodynamic equilibrium. The plasma composition is calculated by stoichiometric approach in which chemical reactions and multiple ionizations are formulated by following mass action law and Saha's equation, respectively. Correction for weakly non‐ideal behavior at high density regime is conducted using the Debye‐Hückel theory. Based on the calculated composition, t

The fast (right-handed) hydromagnetic wave is generated by a Stix coil installed on the Model C stellarator. Maximum wave generation and heating occurs, as expected, under conditions such that the wavelength of the propagating wave equals the wavelength of the coil structure. Measurements of diamagnetic pressure determine the efficiency for conversion of rf power into thermal energy. Theoretical calculations of heating rates shows that plasma resistivity and Landau damping are insufficient to ac

This paper presents a simulation model for the generation of strong pressure wave by means of pulsed spark discharge in water and its application to well cleaning. In the simulation model, one-dimensional time-dependent magnetohydrodynamic equations are coupled to a capacitive discharge circuit equation. A cylindrical conducting spark channel formed by electrical breakdown of water gap between a pair of electrodes is treated as a load of which resistance and inductance are allowed to change with

This paper presents the electrical conductivity data of copper along the gas branch of the binodal curve in the warm dense matter (WDM) regime as a function of mass density and temperature. All data are obtained using the underwater wire explosion technique, in which vaporized copper cools along the gas branch of the binodal curve during the period of current dwell after the wire explodes. Mass density and temperature are measured by fast imaging and optical spectroscopy, respectively. Combining

In volume production H -ion sources, control of electron temperature is essential due to its close correlation with the generation of vibrationally-excited hydrogen molecules in the driver region as well as the generation of H -ions by dissociative attachment in the extraction region.In the ion source group at Seoul National University (SNU) in Korea, a lot of research effort has been made to the development of a volume production H -ion source based on radio-frequency (RF) transformercoupled pl

We estimate the parameters of a Cu plasma generated by an X-pinch by comparing experimentally measured x-rays with synthetic data. A filtered absolute extreme ultraviolet diode array is used to measure time-resolved x-ray spectra with a spectral resolution of ∼1 keV in the energy range of 1–10 keV. The synthetic spectra of Cu plasmas with different electron temperatures, electron densities, and fast electron fractions are calculated using the FLYCHK code. For quantitative comparison with the mea