Modified calculation method using FFT filtering and reconstructing of an interferogram for monitoring a laser-plasma density

류우제,조재흥,Jeong Young Uk,Lee Kitae,Park Seong Hee 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.3

In a laser-plasma electron acceleration, the quality of electron beams is sensitive to the parameters of a laser and a plasma density. With a given laser, higher plasma density may be good for higher charge, while lower density is better for longer acceleration channel, generating higher peak energy at the expense of charge. The dependence of electron beam parameters on the plasma density is, therefore, crucial to find the operating condition for applications. After the target chamber is evacuated, the plasma density and the focal position of the laser beam in the plasma channel can be remotely controlled during the experiments. The plasma density can be obtained by extracting the phase information from captured interferogram, followed by numerically computing the integral derived using Abel inversion. We suggested the simple idea of FFT Filtering and Reconstructing (FR), to be processed prior to a typical computing process, which is the continuous wavelet transform (CWT) for phase shift and the Fourier–Hankel transform (FH) for the integral of Abel inversion here. The FFT filtering can suppress the errors due to the noise, while the reconstructing can select the different data points between the fringes to reduce the systematic error and improve the visibility in interferograms. We confirm the FR-CWT-FH method can provide the average plasma density in uniform region and the longitudinal channel structure with high accuracy, letting the in-situ monitoring possible. The fringe spacing in reconstruction and the wavelet frequency in CWT can be selected differently depending on the shape of plasma density, such as uniform or rising (or falling), and its length of each region to obtain the detailed structure of plasmas.

Analysis of Langmuir Probe Data in High Density Plasmas

김창구 한국화학공학회 2004 Korean Journal of Chemical Engineering Vol.21 No.3

Analysis of Langmuir probe data by using the parametrization of Laframboises numerical results wasperformed to characterize high density plasmas (argon or deuterium discharges) in terms of plasma parameters suchas plasma density and electron temperature. The use of parameterizing Laframboises results was found to readilyextract the plasma parameters for arbitrary ratios of probe radius to Debye length in high density plasmas. It wasobserved that the electron temperature increased with decreasing gas pressure, and was nearly constant with powerin both argon and deuterium plasmas. The plasma density increased with both power and pressure in both argon anddeuterium plasmas. Over the power and pressure ranges used in this work, the plasma density in deuterium plasmaswas found to be an order of magnitude lower than that in argon plasmas. A simulation study showed good agreementof predicted electron temperature and plasma density with experimental results for argon plasmas.

Optimum Conditions of the Plasma Density for the Generation of the Maximum Bunch Charge in a Laser Wakefield Accelerator

유승훈,신현수,김근주,김재훈 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.7

The plasma density effects on the bunch charge in the laser wakefield accelerator were investigated by experiments and simulations. We measured the energy and charge of the quasi-mono energetic electron bunch with energy spectrometer and ICT. Also the plasma density was measured using a biprism interferometer. The measured electron energy showed that the electron energy decreased with increasing plasma density due to the dephasing effect. The results of the bunch charge measurement showed that the effect of the plasma density on the bunch charge was separated into two different density regimes. In the low density regime (<i>cτ/λ_p</i> < 2), the bunch charge increased with the plasma density. In the high density regime (<i>cτ/λ_p</i> > 2), bunch charge decreased with increasing plasma density. There exists an optimum plasma density to generate a high bunch charge. Particle-In-Cell simulations show that the multi-cavitation of the plasma wake wave results in the maximum generation of the bunch charge in the laser wakefield accelerator.

레이저 유도 플라즈마에 대한 자기장 감금의 영향 연구

현은주,김용현 한국전기전자학회 2024 전기전자학회논문지 Vol.28 No.1

"간단한 자기장 감금이 레이저 유도 플라즈마의 전하 입자들에 미치는 영향이 논의 되었다. 자기장 영향에 대한 이전 연구들은 주로 플라즈마 방전 세기의 향상이나 수명시간 연장에 집중되었다. 이와 대조적으로, 본 개발은 과거에 거의 다뤄지지 않았던, 플라즈마 소멸에 대해 연구하였다. 이는 플라즈마를 활용한 기술개발에 혁신적인 도움이 될 것으로 기대한다. Nd:YAG 레이저 (1064 nm, 6 ns) 가 3가지 타입의 금속 물질 (Al, Ti, STS)과 공기 중에 집광되었다.   자석으로 0.4T 크기의 자기장을 만들었고, 이를 레이저 유도 플라즈마에 관통시켰다. 플라즈마 스펙트럼은 레이저 파워와 분광기의 딜레이 타임을 조정해 가면서 자기장 여부에따른 수치가 측정되었다. OⅠ(777.42 nm), FeⅠ(520.447 nm), TiⅠ(503.649 nm), AlⅠ(396.147 nm) 스펙트럼 분석을 통해 자기장에 의한 플라즈마의 소멸이 특정 조건에 상관없이 항상 촉진됨을 독점적으로 발견하였다." "Most previous works about magnetic effect on plasma emission were interested in emission enhancement which was useful to various fields of plasma application. On the contrary, the following work is interested in plasma dissipation rarely reported in prior researches and expected to help advance plasma-controlling technique. Nd:YAG laser (1064 nm, 6 ns) was focused on three kinds of metals (Al, Ti and STS) and air. The permanent magnetic field (0.4 T) of   magnet was provided passing throughout laser-induced plasma. The spectra of plasma in both the presence and absence of the magnetic field were observed with varying laser power and delay time of the spectrograph. In this work it was uniquely discovered that the plasma always dissipated easily in the presence of magnetic field irrespective of the laser power. With the OⅠ(777.42 nm)-line shape function fitted to Lorentz profile, its half width at half maximum (HWHM) was evaluated to verify that the magnetic field increased the plasma density. It is concluded that magnetic field facilitates not only plasma emission enhancement but also plasma dissipation, increasing recombination rate which is proportional to plasma density."

Review of laser-plasma physics research and applications in Korea

Bang W.,Cho B. I.,Cho M. H.,Cho M. S.,Chung M.,Hur M.S.,Kang G.,Kang K.,Kang T.,Kim C.,Kim H. N.,Kim J.,Kim K. B.,Kim K. N.,Kim M.,Kim M. S.,Kumar M.,Lee H.,Lee H. W.,Lee K.,Nam I.,Park S. H.,Phung V. 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.8

Laser plasmas can be produced when high-power laser beams are focused in matter. A focused laser beam of TW(terawatt)- level high power has an extremely strong electric field, so neutral atoms are immediately ionized by the laser electric field, leading to a laser-produced plasma. The laser plasma can be produced by small table-top TW lasers based on the CPA (chirped-pulse amplification) technique, and now they are rather easily available even in university laboratories. In Korea, there are several CPA-based TW (or even petawatt) lasers in a few institutions, and they have been used for diverse laser plasma physics research and applications, including the laser acceleration for electrons and ions, high-power THz (tera-hertz) generation, advanced light sources, high-energy-density plasmas, plasma optics, etc. This paper reviews some of the laser plasma physics research and applications that have been performed in several universities and research institutes.

The application of magnetic field at low pressure for optimal laser-induced plasma spectroscopy

Kim, Dae-Hyoung,Kihm, Yong H.,Choi, Soo-Jin,Choi, Jae-Jun,Yoh, Jack J. Elsevier 2015 Spectrochimica acta. Part B, Atomic spectroscopy Vol.110 No.-

<P><B>Abstract</B></P> <P>The application of magnetic field in controlling the charged particles of the laser induced plasma is considered. The chara\cteristics of the plasma depend on the electron density and its recombination. The magnetic field effects as well as the ambient pressure are the key factors for determining the electron density of the plasma. Two different laser energies (Low: 30mJ/pulse, High: 140mJ/pulse) and the pressure range between 760Torr and 10Torr are used when focusing a Nd:YAG laser beam (1064nm, 6ns) onto the metal samples where the applied magnetic field varied between 0.1 and 0.5Tesla. At 760Torr, the plasma signal enhancement was obtained in the presence of magnetic field when the laser energy was low. With a lowered pressure however, the signal enhancement due to a magnetic field was achieved regardless of the laser energy. The enhancement of the signal in the presence of magnetic field is related to the electron density and the high frequency instability which are controlled by the ambient pressure and magnetic field intensity. In this paper, the optimal conditions for the laser-induced plasma spectroscopy in the magnetic field at various low pressures are discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> With magnetic field, LIBS signal enhancement is sensitive to the laser energy </LI> <LI> At low pressure, signal enhancement with magnetic field is insensitive to the laser energy </LI> <LI> The electron density is analyzed to explain the observed signal intensity variation </LI> </UL> </P>

Dosimetric Properties of Plasma Density Effects on Laser-Accelerated VHEE Beams Using a Sharp Density-Transition Scheme

류승훈,민병준,조성호,김은호,박정훈,정원균,김근범,김금배,김재훈,정호진,이기태,박성용 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.1

In this paper, the effects of the plasma density on laser-accelerated electron beams for radiation therapy with a sharp density transition are investigated. In the sharp density-transition scheme for electron injection, the crucial issue is finding the optimum density conditions under which electrons injected only during the first period of the laser wake wave are accelerated further. In this paper, we report particle-in-cell simulation results for the effects of both the scale length and the densitytransition ratio on the generation of a quasi-mono-energetic electron bunch. The effects of both the transverse parabolic channel and the plasma length on the electron-beam’s quality are investigated. Also, we show the experimental results for the feasibility of a sharp density-transition structure. The dosimetric properties of these very high-energy electron beams are calculated using Monte Carlo simulations.

Inverse Bremsstrahlung 과정을 활용한 고밀도 플라즈마의 전자밀도 계측 기술

김견호(Kyun-Ho Kim),봉철우(Cheolwoo Bong),박문수(Moon Soo Bak) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11

An experimental study on a method to accurately measure the spatiotemporal evolution of electron density in a highdensity plasma using a diode laser based on the inverse Bremsstrahlung process was carried out in a laser-induced plasma (LIP) produced under atmospheric pressure in air. First, the radial absorption coefficients were obtained from the tomographic reconstruction based on the absorbance traces collected along multiple, different laser paths around the plasma. Then, the temporal profiles of electron density at different radial positions within the plasma were then derived from these radial absorption coefficients. The extent of absorption of laser energy by the plasma was significant, allowing for measurements of electron densities exceeding 10<SUP>18</SUP> ㎝<SUP>−3</SUP>, while also suggesting that the method can be employed as a diagnostic tool for monitoring high-density plasmas.

유기물 광전소자 제작을 위한 박스 캐소드 스퍼터 기술

김한기,Kim, Han-Ki 한국전기전자재료학회 2006 전기전자재료학회논문지 Vol.19 No.4

We report on plasma damage free-sputtering technologies for organic light emitting diodes (OLEDs), organic thin film transistor (OTFT) and flexible displays by using a box cathode sputtering (BCS) method. Specially designed BCS system has two facing targets generating high magnetic fields ideally entering and leaving the targets, perpendicularly. This target geometry allows the formation of high-density plasma between targets and enables us to realize plasma damage free sputtering on organic layer without protection layer against plasma. The OLED with Al cathode prepared by BCS shows electrical and optical characteristics comparable to OLED with thermally evaporated Mg-Ag cathode. It was found that OLED with Al cathode layer prepared by BCS has much lower leakage current density ($1{\times}10^{-5}\;mA/cm^2$ at -6 V) than that $(1{\times}10^{-2}{\sim}-10^0\;mA/cm^2)$ of OLED prepared by conventional DC sputtering system. This indicates that BCS technique is a promising electrode deposition method for substituting conventional thermal evaporation and DC/RF sputtering in fabrication process of organic based optoelectronics.

Low-temperature direct synthesis of high quality WS₂ thin films by plasma-enhanced atomic layer deposition for energy related applications

Yeo, Seungmin,Nandi, Dip K.,Rahul, R.,Kim, Tae Hyun,Shong, Bonggeun,Jang, Yujin,Bae, Jong-Seong,Han, Jeong Woo,Kim, Soo-Hyun,Kim, Hyungjun Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.459 No.-

<P><B>Abstract</B></P> <P>Tungsten disulfide (WS<SUB>2</SUB>) thin films are grown on several types of substrates by plasma-enhanced atomic layer deposition (PEALD) technique using tungsten hexacarbonyl [W(CO)<SUB>6</SUB>] and H<SUB>2</SUB>S plasma at a relatively low temperature of 350 °C. The method delivers polycrystalline WS<SUB>2</SUB> film with (0 0 2) preferential growth and the high quality films could be successfully grown with as low as 30 ALD cycles (corresponding to ∼3 nm of thickness). Density functional theory (DFT) calculation results reveal that both adsorption of W(CO)<SUB>6</SUB> and removal of CO ligand would be facilitated by usage of H<SUB>2</SUB>S plasma by generating the different defect sites on the basal plane. The typical self-limiting film growth (growth rate of ∼0.1 nm/cycle), characteristic of ideal ALD, is clearly observed with both the precursor and reactant pulsing time. X-ray diffractometry (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS) are performed in details to study the as-grown WS<SUB>2</SUB> film on Si/SiO<SUB>2</SUB> substrate. The analysis results confirm the formation of polycrystalline film, with high purity and well-defined stoichiometry. The as-deposited WS<SUB>2</SUB> films are then explored as an electrode in the field of energy generation as well as energy storage. The films are uniformly and conformally grown on high surface-area 3 dimensional Ni-foam that show excellent activity towards hydrogen evolution reaction (HER). Significantly low overpotential of ∼280 mV is observed at a high operational current density of 100 mA cm<SUP>−2</SUP> during HER in acid electrolyte. In addition, the as-grown films on stainless steel substrate also reveal the stable electrochemical performances in Na-ion battery as an anode with reasonably high areal capacity of ∼44.5 μAh cm<SUP>−2</SUP> at the end of 50 charge-discharge cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PEALD grown polycrystalline WS<SUB>2</SUB> using W(CO)<SUB>6</SUB> precursor and H<SUB>2</SUB>S plasma as a reactant. </LI> <LI> H<SUB>2</SUB>S plasma to facilitate ALD reaction elucidated from DFT calculation. </LI> <LI> Excellent uniformity and conformality of PEALD-WS<SUB>2</SUB> on 3 dimensional Ni-foam. </LI> <LI> Applications as a binder and carbon-free anode in SIBs and catalyst for HER. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>