• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.22-24
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• 1998

The current distribution in the source coil region is analyzed using the two dimensional finite element method. The variables in the FEM are the magnetic vector potentials and the source current density. The boundary condition for the source current density is that the total current is the sum of the eddy current and the source current and is known quantity from measurement. The simulation results are compared with the analytical solution. It is found that the method can analyze the current distribution in the source conductors very accurately.

• Nuclear Engineering and Technology
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• v.35 no.3
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• pp.226-233
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• 2003

The discharge characteristics of a prototype ion source was investigated, which was developed and upgraded for the NBI (Neutral Beam Injection) heating system of KSTAR (Korea Superconducting Tokamak Advanced Research). The ion source was designed for the arc discharge of magnetic bucket chamber with multi-pole cusp fields. The ion source was discharged by the emission-limited mode with the control of filament heating voltage. The maximum ion density was 4 times larger than the previous discharge controlled by a space-charge-limited mode with fully heated filament. The plasma (ion) density and arc current were proportional to the filament voltage, but the discharge efficiency was inversely proportional to the operating pressure of hydrogen gas. The maximum ion density and arc current were obtained with constant arc voltage ($80{\sim}100V$), as $8{\times}10^{11}cm^{-3}$ and 1200 A, respectively. The estimated maximum beam current was about 35 A, extracted by the accelerating voltage of 80kV.

• Journal of Biomedical Engineering Research
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• v.27 no.1
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• pp.30-37
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• 2006

Injecting currents into an electrically conducting subject, we may measure the induced magnetic flux density distributions using an MRI scanner. The measured data are utilized to reconstruct cross-sectional images of internal conductivity and current density distributions in Magnetic Resonance Electrical Impedance Tomography (MREIT). Injection currents are usually provided in a form of mono-polar or bi-polar pulses synchronized with an MR pulse sequence. Given an MRI scanner performing the MR phase imaging to extract the induced magnetic flux density data, the current source becomes one of the key parts determining the signal-to-noise ratio (SNR) of the measured data. Since this SNR is crucial in determining the quality of reconstructed MREIT images, special care must be given in the design and implementation of the current source. This paper describes a current source design for MREIT with features including interleaved current injection, arbitrary current waveform, electrode switching to discharge any stored charge from previous current injections, optical isolation from an MR spectrometer and PC, precise current injection timing control synchronized with any MR pulse sequence, and versatile PC control program. The performance of the current source was verified using a 3T MRI scanner and saline phantoms.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.1
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• pp.9-14
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• 2000

When current flows through a thick conductor such, most of the current flows along outside of the conductor, which is called skin effect. This paper represents a method calculating such a current distribution in the conductor region. The conductor region is divided into some pieces and each piece has its own unknown variable, i.e. current density. The governing equation which expresses Maxwell's equation is combined with the circuit equation with voltage source. The combined equation is solved to obtain current distribution in the conductor. This algorithm is applied to EMC(Electromagnetic Casting) to calculate current density with voltage source.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1609-1611
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• 1994

In ECR and helicon reactors for plasma processing, a high density plasma is generated in a source region which is connected to a diffusion region where the processing takes place. Large density and potential gradients can develop at the orifice of the source which drive ion currents into the diffusion region. The average ion velocity may become the order of the sound velocity. Measurements of the ion saturation current to a Langmuir probe are used as a standard method of determining the plasma density in laboratory discharges. However, the analysis becomes difficult in a steaming plasma. We have used the HAMLET plasma simulator to simulate the ion flow to a large langmuir probe in an ECR plasma. The collection surface was aligned with the Held upstream, normal to the field, and downstream. ion trajectories through the electric and magnetic fields were calculated including ion-neutral collisions. We examines the ratio of ion current density to plasma density as a function of magnetic field and pressure.

• Nuclear Engineering and Technology
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• v.51 no.8
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• pp.1978-1982
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• 2019

The paper presents the electrical performance measurements of a prototype nuclear battery and two types of betavoltaic cells. The electrical performance was assessed by measuring current-voltage properties (I-V) and determining the short-circuit current and the open-circuit voltage. With ⁶³Ni as an irradiation source, the open-circuit voltage and the short-circuit current were determined as 1 V and 64 nA, respectively. The prototype consisted of 10 betavoltaic cells that were prepared using radioactive ⁶³Ni. Electroplating of the radioactive ⁶³Ni on an ohmic contact (Ti-Ni) was carried out at a current density of 20 mA/㎠. Two types of betavoltaic cells were studied: with an external ⁶³Ni source and a ⁶³Ni-covered source. Under irradiation of the ⁶³Ni source with an activity of 10 mCi, the open-circuit voltage V_oc of the fabricated cells reached 151 mV and 109 mV; the short-circuit current density J_sc was measured to be 72.9 nA/cm2 and 64.6 nA/㎠, respectively. The betavoltaic cells had the fill factor of 55% and 50%, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.271-271
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• 2012

Many studies have been investigated on high density plasma source (Electron Cyclotron Resonance, Inductively Coupled Plasma, Helicon plasma) for large area source after It is announced that productivity of plasma process depends on plasma density. In this presentation, we will propose the new concept of the multiple source, which consists of a parallel connection of ICP sources and helicon plasma sources. For plasma uniformity, equivalent power (especially, equivalent current in ICP & Helicon) should distribute on each source. We design power feeding line as coaxial transmission line with same length of ground line in each source for equivalent power distribution. And we confirm the equivalent power distribution with simulation and experimental result. Based on basic study, we develop the plasma source for oxidation in semiconductor process. we will discuss the relationship between the processing parameters (With or WithOut magnet, operating pressure, input power ). In ICP, plasma density uniformity is uniform. In ICP with magnet (or Helicon) plasma density is not uniform. As a result, new design (magnet arrangement and gas distributor and etc..) are needed for uniform plasma density in ICP with magnet and Helicon.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.3
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• pp.383-388
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• 2011

The cold hollow cathode gas ion source is under development for multi aperture focused ion beam (FIB) system. In this paper, we describe the cold hollow cathode ion source design and the general ion source performance using Ar gas. The glow discharge characteristics and the ion beam current density at various operation conditions are investigated. This ion source can generate maximum ion beam current density of approximately 120 mA/$cm^2$ at ion beam potential of 10 kV. In order to effectively transport the energetic ions generated from the ion source to the multi-aperture focused ion beam(FIB) system, the einzel lens system for ion beam focusing is designed and evaluated. The ions ejected from the ion source can be forced to move near parallel to the beam axis by adjusting the potentials of the einzel lenses.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.105-109
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• 2012

The current status of the AKARI-FIS Point Source Catalogue is reported. The first version of the Bright Source Catalogue has been in public since March 2010 and used extensively in the various fields in astronomy. The second version of the Bright Source Catalogue and the first version of the Faint Source Catalogue are currently under development. The revised Bright Source Catalogue is expected to have improved completeness, reliability, and accuracy compared to the current version. The Faint Source Catalogue will have a scan-density dependent detection limit and will enable much deeper exploration of the sky especially in the high-ecliptic latitude regions. Both catalogues will be available in a year time scale.

• Journal of Biomedical Engineering Research
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• v.25 no.3
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• pp.165-169
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• 2004

In Magnetic Resonance Electrical Impedance Tomography (MREIT), we inject current through electrodes placed on the surface of a subject and measure the induced magnetic flux density distribution using an MRI scanner. This requires a constant current source whose output pulses are synchronized with MR pulse sequences. In this paper, we present a design and performance analysis of a current source used in a 3.0T MREIT system. The developed current source was tested using a saline phantom. We found that its performance is satisfactory for the current MREIT system. We suggest future improvements for better SNR(signal-to-noise ratio).