• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.47.2-47.2
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• 2016

The protons and helium ions in the solar wind are observed to possess anisotropic temperature profiles. The anisotropy appears to be limited by various marginal instability conditions. One of the efficient methods to investigate the global dynamics and distribution of various temperature anisotropies in the large-scale solar wind models may be that based upon the macroscopic quasi-linear approach. The present paper investigates the proton and helium ion anisotropy instabilities on the basis of comparison between the quasi-linear theory versus particle-in-cell simulation. It is found that the overall dynamical development of the particle temperatures is quite accurately reproduced by the macroscopic quasi-linear scheme. The wave energy development in time, however, shows somewhat less restrictive comparisons, indicating that while the quasi-linear method is acceptable for the particle dynamics, the wave analysis probably requires higher-order physics, such as wave-wave coupling or nonlinear wave-particle interaction. We carried out comparative studies of proton firehose instability, aperiodic ordinary mode instability, and helium ion anisotropy instability. It was found that the agreement between QL theory and PIC simulation is rather good. It means that the quasilinear approximation enjoys only a limited range of validity, especially for the wave dynamics and for the relatively high-beta regime.

• Geophysics and Geophysical Exploration
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• v.24 no.2
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• pp.35-44
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• 2021

As the execution speed of Python is slower than those of other programming languages (e.g., C, C++, and FORTRAN), Python is not considered to be efficient for writing numerical geodynamic code that requires numerous iterations. Recently, many computational techniques, such as the Just-In-Time (JIT) compiler, have been developed to enhance the calculation speed of Python. Here, we developed two-dimensional (2D) numerical geodynamic code that was optimized for the JIT compiler, based on Python. Our code simulates mantle convection by combining the Particle-In-Cell (PIC) scheme and the finite element method (FEM), which are both commonly used in geodynamic modeling. We benchmarked well-known mantle convection problems to evaluate the reliability of our code, which confirmed that the root mean square velocity and Nusselt number obtained from our numerical modeling were consistent with those of the mantle convection problems. The matrix assembly and PIC processes in our code, when run with the JIT compiler, successfully achieved a speed-up 30× and 258× faster than without the JIT compiler, respectively. Our Python-based FEM-PIC code shows the high potential of Python for geodynamic modeling cases that require complex computations.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.602-605
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• 2008

The anode sheath structure in the hollow anode of an anode-layer type Hall thruster was numerically computed using a fully kinetic 2D3V Particle-in-Cell and Direct Simulation Monte Carlo(PIC-DSMC) code. By treating both ions and electrons as particles, anode surface region, which is electrically non-neutral, was analyzed. In order to analyze in detail, the calculation code was parallelized using Message Passing Interface (MPI). The code successfully simulated the discharge current oscillation. In the low magnetic induction case, ion sheath appears in the anode surface because ionization is enough to maintain the plasma occurs in the anode hollow. As the magnetic induction increases, main ionization region move to outside of the anode. At the same time, anode sheath voltage decreases. In the high magnetic induction case, electron sheath appears on the anode surface periodically because the ionization occurs mainly in the discharge channel. This anode sheath condition shift can be explained using the simple sheath model.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.118.2-118.2
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• 2012

In particle-in-cell (PIC) simulation studies related to ion-ion two-stream instability, a reduced ion-to-electron mass ratio is often employed to save computation time. But it was not clearly verified how electrons dynamics are coupled with the slower evolution of ion-ion interactions under the external electric field. We have studied the ion beam driven instability using a 1D electrostatic PIC code by comparing different rescaling of parameter with real ion mass from the reference simulation with reduced ion mass. As the external electric field is stronger, the excited unstable mode range was more sensitively affected by the system size with the real mass ratio than the reduced ion mass. The results show that the reduced mass ratio should be used cautiously in PIC code as the electron dynamics can modify the ion instabilities. Additionally we found the formation of electron flat-top distribution in the final saturation stage. Simulation results show that in the early phase electrostatic solitary waves are quasi-periodically formed, but later they are fully dissipated resulting in heated, flat-top distributions. New electron beam components are occasionally formed. These are a consequence of the interaction with solitary wave structures. We parametrically investigate the development of electron phase space distributions for various drift speeds of ion beams and temperature ratios between ions and electrons

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.454-454
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• 2012

Magnetron sputtering에서, 영구자석의 자속은 target 표면 가까이에 전자를 구속한다. 구속된 전자는 Ar중성기체와 충돌하여 Ar이온을 발생시킬 수 있으므로, target 근처에서의 플라즈마 밀도를 높여, 자석이 없을 때보다 낮은 압력 또는 낮은 전압에서 방전할 수 있다. 구속 전자가 밀집된 공간에서 sputtering 현상이 주로 발생하기 때문에, planar target을 사용할 경우에는 target이 불균일하게 식각되어 target의 사용효율이 좋지 못하다. 이에 대한 한 가지 대안은 target을 원통형으로 만들어 회전시키는 것이다. Cylindrical target 의 내부에 위치한 영구자석은 고정시키고, target만을 회전시키면 비교적 균일하게 식각되므로 target의 사용효율을 높일 수 있다. 본 연구에서는 기존의 planar target에 대한 Particle-In-Cell Simulation을 Cylindrical target 에 적용시키기 위한 방법을 알아본다. 또한, 개발된 Simulator를 이용하여, Sputtering 조건의 변화에 대한 I-V curve의 변화를 살펴본다.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.29.3-29.3
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• 2011

The turbulence in the nonlinear regime of the electromagnetic ion-cyclotron (EMIC) instability are investigated via a particle-in-cell (PIC) simulation. EMIC instability arises from anisotropic ion temperature and excites the Alfven ion-cyclotron (AIC) waves. The excited AIC waves undergo inverse-cascade via the nonlinear wave interaction of two AIC and one ion density modes. Induced ion density modes are the normal and second harmonic ion-acoustic (IA) waves. They have the same group velocity, but the second harmonic IA mode only generates the longitudinal electric field.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.98-98
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• 2010

대기압 상에서의 방전은 기존의 진공 장비를 요구하던 플라즈마 장비들에 비해 경제적이고 간편해서 물질의 표면 처리 및 바이오 응용 플라즈마 등에서 널리 사용되고 있다. 본 연구에서는 평판형 방전으로 발생되는 플라즈마의 물리적 성질을 확인하기 위해 1차원 Particle-In-Cell (PIC) 시뮬레이션을 이용하였다. PIC 시뮬레이션은 계산시간이 많이 걸리는 단점이 있으나 가정이 거의 없기 때문에 정확한 계산값을 얻을 수 있는 장점이 있다. 주파수를 13.56 MHz에서 100 MHz 까지 변화 시켰고, 입력신호는 정현파와 직류 펄스로 하였다. 정현파에 비해서 펄스형 신호를 인가했을 때 전자, 이온 밀도가 시간에 따라서 급격히 변하는 것이 관찰되었다. 또한 전극 앞에 유전체가 있을 경우, 입력 신호의 변화보다 플라즈마 밀도의 변화가 다소 지연되었다. 이 외에도 여기종 분포, 전자 온도 등의 시공간적 특성을 관찰하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.243.1-243.1
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• 2014

For two-dimensional grid electrodes immersed in plasmas, sheath expansion due to negative high-voltage pulse applied to the electrode generates high-energy pseudowave. The high-energy pseudowave can be used as ion beam for ion implantation. To estimate ion dose due to high-energy pseudowave, investigation on sheath expansion of grid electroes is necessary. To investigate sheath expansion, an analytic model was developed by Vlasov equation and applying the 1-D sheath expansion model to 2-D. Because of lack of generalized 2-D Child-Langmuir current, model cannot give solvable equation. Instead, for a given grid electrode geometry, the model found the relations between ion distribution functions, Child-Langmuir currents, and sheath expansions. With these relations and particle-in-cell (PIC) simulations, for given grid electrode geometry, computation time was greatly reduced for various conditions such as electrode voltages, plasma densities, and ion species. The model was examined by PIC simulations and experiments, and they well agreed.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1782-1784
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• 1997

Using particle-in-cell(PIC) and Monte Carlo collision(MCC), we investigate the trajectory of electrons and the characteristics of D.C. discharge In Wire Ion Plasma Source(WIPS).

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.529-529
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• 2013

플라즈마를 진단하는 데에는 장비적으로나 현실적으로 많은 제약이 따른다. 따라서 측정 할 수 있는 parameter가 적다. 그리고 진단 장비의 성능에 따라서 측정된 data의 신뢰도가 결정된다. 그래서 플라즈마에 레이저를 쏘아서 생성되는 솔리톤의 RADIATION을 이용하여 플라즈마의 특성을 파악하려고 한다. 본 시뮬레이션은 Particle-In-Cell (PIC) 시뮬레이션을 이용하여 Underdense 플라즈마에 Terahertz 레이저를 쏘았을 경우 발생되는 솔리톤의 특성을 파악하였다. 2D 시뮬레이션으로 수행하였으며 플라즈마는 Underdense 플라즈마를 이용하였다. 레이저 Focusing 점의 위치와 솔리톤의 주파수, 플라즈마의 밀도 gradient 에 따른 솔리톤의 이동 및 특징, 플라즈마 밀도에 따른 솔리톤의 특징을 살펴보았다.