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Stability Analysis of a C-band 500-kW Klystron with a Multi-Cell Output Cavity
Jihyun Hwang,Sung-Ju Park,Won Namkung,Moohyun Cho 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.6
A prototype 5-GHz 500-kW CW klystron (model E3762 provided by Toshiba Electron Tubes & Devices Co. Ltd.) has been operating as the RF source for the lower hybrid current drive (LHCD) system in the KSTAR tokamak. A cavity design study is being carried out with a simulation code based on the main klystron’s operation parameters in order to investigate how the efficiency of the 5-GHz 500-kW CW klystron prototype can be enhanced. This is being done by simulating the klystron’s performances for various cavity parameters, including the number of cavities, the inter-cavity distance, and the cavity’s tuning frequencies. The simulation has been done with the FCI (field charge interaction) code aided by a matlab script for scanning input parameters. The initial set of scan parameters was obtained by benchmarking the E3762 klystron, and we are able to obtain optimized design parameters for a cavity system with better efficiency by adopting a multi-cell output cavity. However, the multi-cell output cavity is prone to self-oscillations due to the prolonged (several half RF periods) beam-field interaction along its multiple gaps. We have checked the feasibility of the optimization by evaluating the stability of the output cavity system. The stability is given by the ratio of a beam-loading conductance to the circuit conductance.
Jihyun Hwang,Eunji Choi,Sohee Lee,Hyang Sook Chun,Sangdoo Ahn,Byung Hee Kim 한국식품영양과학회 2021 한국식품영양과학회 학술대회발표집 Vol.2021 No.10
This study sought to identify adulterated red pepper powder (RPP) containing undeclared ingredients, such as salts, glucose, Monascus red pigments, and other plant ingredients(e.g., wheat flour, garlic powder, onion powder) using element and sugar analysis methods. Analytical data were obtained for 66 samples of authentic RPP and 12 samples of artificially manufactured RPP. The variables selected to best identify the authenticity of RPP include Na, Cl, K, maltohexaose, and maltoheptaose, which partly or totally originate from RPP, salts, or Monascus red pigments. Collectively, our findings suggest that combined analyses of the above five constituents could be used to identify adulterated RPP containing undeclared ingredients.
Design of a High-Eciency S-band Klystron with a Multi-cell Output Cavity
Jihyun Hwang,Sung-Ju Park,Won Namkung,Moohyun Cho 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.8
As large-scale scientific facilities develop, the klystron eciency becomes an important issue to reduce high operating costs. We are developing high-eciency klystrons for the Pohang Light Source-II (PLS-II) and the Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL) at the Pohang Accelerator Laboratory (PAL). The newly developed klystrons should have the same specifications, including perveance and overall length, to replace existing ones. Under these limited conditions, we designed the klystrons based on a multi-cell output cavity to improve the power-conversion eciency significatly. We simulated the beam-dynamics using the Field Charge Interaction (FCI) code with a MATLAB script to find the optimum design parameters for high eciency. We have determined the design parameters, such as cell tuning frequencies, inter-cell distances, couplings between cells and the Qe of the last cell, of the multi-cell output cavity .
Compact Hexagonal Liquid Core PCF Package Using a Hollow Optical Fiber
Hwang, Jihyun,Park, Jiyoung,Nazari Baresari, Tavakol,Han, Seung-Ryong,Jhon, Young Min,Oh, Kyunghwan IEEE 2018 Photonics Technology Letters Vol.30 No.8
<P>We proposed and demonstrated a novel method to package liquid-core hexagonal photonic crystal fibers (PCFs) by utilizing a hollow optical fiber (HOF) not only as a liquid delivery tube but also as a light launching pedestal. Compact all-fiber packaging with single mode fiber input and output was experimentally achieved. Various configurations of liquid core PCFs were demonstrated by controlling the inner diameter of HOF and offsets. Based on numerical analyses and light launching experiments, we confirmed that this method could substantially enhance the light–liquid interaction efficiency, structurally prevent liquid evaporation within PCF, and providing a new versatile liquid core PCF device platform.</P>
Teaching the Intermediate Value Theorem with Non-Existing Examples
( Jihyun Hwang ),( Dae S. Hong ) 한국수학교육학회 2020 수학교육연구 Vol.23 No.1
In this case study, a professor was observed to investigate use of instructional examples when teaching the Intermediate Value Theorem in a calculus course. Video-recorded lessons were analyzed with constant comparison to video-stimulated recall interviews and field notes. The professor employed multiple instructional examples, which was initiated by students and modified by the professor. The professor asked students to build non-existing examples as an informal proof of the Intermediate Value Theorem and assessment of students’ previous knowledge. Use of incorrect examples on instructional purpose can be an appropriate way for formative assessment as well as a bridge between informal and formal proofs in college mathematics.
Jihyun Hwang,Heeju Jun,Seoye Roh,Seong Jae Lee,Jeong Min Mun,Seung Wook Kim,Min-Yu Chung,In-Hwan Kim,Byung Hee Kim 한국식품영양과학회 2021 한국식품영양과학회 학술대회발표집 Vol.2021 No.10
We prepared 1,3-dipalmitoyl-2-oleoyl glycerol (POP)-rich fats with reduced levels of diacylglycerols (DAGs), adversely affecting the tempering of chocolate, via two-step hexane fractionation of palm stearin. Cocoa butter equivalents (CBEs) were fabricated by blending the as-prepared fats with 1,3-distearoyl-2-oleoyl glycerol (SOS)-rich fats obtained by hexane fractionation of degummed shea butter. POP-rich fats achieved under the best conditions for the fractionation of palm stearin had a significantly lower DAG content (1.6 w/w%) than that in the counterpart (4.6 w/w%) prepared by the previously reported method. The CBEs fabricated by blending the POP- and SOS-rich fats in a weight ratio of 40:60 contained 63.7 w/w% total symmetric monounsaturated triacylglycerols, and 1.3 w/w% DAGs, which was not substantially different from the DAG content in cocoa butter (1.1 w/w%). Based on the solid-fat content results, it was concluded that, when these CBEs were used for chocolate manufacture, they blended with cocoa butter at levels up to 40 w/w%, without distinctively altering the hardness and melting behavior of cocoa butter.