Editorial Material
Optics
Andreas Doepp
Summary: Plasma accelerators driven by high-power lasers can produce high-energy electron beams in a smaller scale compared to traditional RF accelerators. However, the performance of these accelerators is limited by laser diffraction. Laser-generated plasma waveguides and controlled electron injection methods can address this issue and demonstrate the potential of novel laser-plasma optics.
LIGHT-SCIENCE & APPLICATIONS
(2022)
Article
Nuclear Science & Technology
H. Frerichs, J. Van Blarcum, S. M. Yang, J-k. Park, N. C. Logan, Y. Feng, O. Schmitz
Summary: The striation pattern of heat loads on divertor targets depends on the plasma response to external resonant magnetic perturbations applied for ELM suppression. Analysis shows that the extent of this pattern is sensitive to the radial location of equilibrium truncation, and a smaller extent is found if the truncation is closer to the separatrix. Simulations demonstrate that by adjusting RMP coil parameters, the peak heat load can be reduced within the range of ELM suppression.
NUCLEAR MATERIALS AND ENERGY
(2023)
Article
Engineering, Aerospace
Smitha V. Thampi, Vrinda Mukundan
Summary: This paper investigates an ionospheric storm initiated by successive CME eruptions, which caused a G3 space weather event on December 19-21, 2015. Observations and measurements from SWARM-A satellite and TIMED/GUVI reveal longitudinal and hemispherical differences in the ionospheric response to the storm, with positive and negative storms observed over different regions. The net effect of disturbance dynamo electric field and composition differences plays an important role in explaining the observed variability in topside ionospheric densities, along with Te variations as a consequence of the space weather event.
ADVANCES IN SPACE RESEARCH
(2023)
Article
Computer Science, Artificial Intelligence
Azarakhsh Jalalvand, Joseph Abbate, Rory Conlin, Geert Verdoolaege, Egemen Kolemen
Summary: Researchers demonstrated through experiments that reservoir computing (RC) in the DIII-D tokamak achieves comparable predictive results to state-of-the-art deep learning models, such as CNNs and LSTMs, with a simpler and quicker training process. This efficient approach allows for rapid adaptation to different scenarios.
IEEE TRANSACTIONS ON NEURAL NETWORKS AND LEARNING SYSTEMS
(2022)
Article
Nuclear Science & Technology
Seung-Ju Lee, Giil Kwon, Sang-won Yun, Taegu Lee, Sang-hee Hahn, Hyunsun Han, Hyunsik Ahn, Jongkook Jin, Dongkeun Lee, Young-jin Kim, Jaesic Hong, Woong-Ryol Lee, Taehyun Tak
Summary: The ITER Real-Time Framework (RTF) is a middleware used for developing fast real-time control applications like the plasma control system (PCS). It allows applications to be built using Function Blocks (FBs) and configured to operate in real-time mode with multi-threading, multi-processing, or multi-node processing. This paper demonstrates the capabilities of RTF in controlling the Poloidal Field (PF) coil Magnetic Power Supply (MPS) system of KSTAR. The RTF application successfully implemented the control logic for 11 PF coils with a 20 KHz execution cycle and integrated real-time network interfaces.
FUSION ENGINEERING AND DESIGN
(2023)
Article
Engineering, Chemical
Yun-peng He, Wei Jin, Yi-bo Wang, Shao-bo Lv, Rui-sheng Wang, Jun-qi Liu, Hai-cheng Liu
Summary: The mechanism of how a magnetic field and a grid affect the electron density and temperature has been studied through simulations and experiments. The results show that the magnetic field constrains electron mass, leading to an increase in collision chances with gas and an increase in ionization rate. This, in turn, reduces the electron temperature. On the other hand, the grid has a more significant influence, causing a sharp decrease in electron density and temperature.
PLASMA CHEMISTRY AND PLASMA PROCESSING
(2023)
Article
Physics, Multidisciplinary
Koji Kikuchi, Hiroshi Akatsuka
Summary: In this study, Tsallis statistics were applied to non-equilibrium plasmas to determine excited-state population distribution and temperature. The results showed that Tsallis statistics well captured the non-equilibrium characteristics in the high-energy region, which differed significantly from the Boltzmann distribution.
Article
Physics, Fluids & Plasmas
Sean M. Donnelly, Nicolas A. Lopez, I. Y. Dodin
Summary: The newly proposed metaplectic geometrical optics (MGO) framework restores the accuracy of geometrical optics near caustics, evaluates wave behavior through numerical methods, and enhances the precision of previously derived analytical approximations.
Article
Chemistry, Physical
Inho Seong, Si-jun Kim, Youngseok Lee, Chulhee Cho, Wonnyoung Jeong, Yebin You, Minsu Choi, Byeongyeop Choi, Shinjae You
Summary: Investigating the quenching of electron temperature in plasma processing is crucial for controlling electron temperature and improving the efficiency of plasma material processing.
Article
Physics, Multidisciplinary
I. S. Tupitsyn, A. M. Tsvelik, R. M. Konik, N. Prokof'ev
Summary: This paper presents a diagrammatic Monte Carlo technique for computing finite-temperature response functions directly on the real-frequency axis, without limitations on the type and nature of the system's action or diagram classes. By eliminating the need for numerical analytic continuation, the scheme allows for the study of spectral densities in frequency-dependent effective interaction models with controlled accuracy.
PHYSICAL REVIEW LETTERS
(2021)
Article
Physics, Applied
Fan Wu, JiaYin Li, FengWu Liu, XinPei Lu
Summary: This paper investigates the ignition phase of a plasma scalpel by analyzing the electrical waveforms, vaporization dynamics, plasma production, and the plasma spectrum. Two types of vapor layers are formed during plasma production, one generated by Joule heating and the other by plasma heating. The study reveals that a thin vapor layer can sustain the plasma and the electron density is estimated at about 7.1 x 10(15) cm(-3) based on the broadening of the H-alpha line.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Physics, Multidisciplinary
Hiroshi Akatsuka, Yoshinori Tanaka
Summary: In this study, the electron temperature of weakly-ionized oxygen and nitrogen plasmas is reconsidered based on thermodynamics and statistical physics. The electron energy distribution function (EEDF) is calculated using the integro-differential Boltzmann equation, and the self-consistent electron mean energy U and entropy S are determined. The statistical electron temperature T-e(st) is then calculated using Gibbs's formula, and the difference between T-e(st) and the electron kinetic temperature T-e(kin) is discussed, along with the temperature corresponding to the slope of the EEDF for each value of E / N.
Article
Materials Science, Coatings & Films
M. Naeem, Madiha Qadeer, Zaka-ul-islam Mujahid, N. U. Rehman, J. C. Diaz-Guillen, R. R. M. Sousa, M. Shaftq
Summary: Cathodic cage plasma nitriding (CCPN) is an efficient technique to improve the surface properties of materials. Pulsed voltage sources are usually used to control the nitrided layer and the discharge transition. Time-resolved plasma diagnostics are important for monitoring plasma parameters, but their fundamental diagnostics are limited.
SURFACE & COATINGS TECHNOLOGY
(2023)
Article
Chemistry, Multidisciplinary
Sung Il Cho, Hyun Keun Park, Surin An, Sang Jeen Hong
Summary: Plasma is crucial in semiconductor processes, especially in the miniaturization and integration of devices. However, the increase in wafer surface temperature caused by the high RF power has posed challenges to the etching process. This study investigates the plasma characteristics using invasive and non-invasive diagnostic methods and proposes a real-time calculation of heat flux to anticipate wafer temperatures and address ion heating issues.
APPLIED SCIENCES-BASEL
(2023)
Article
Physics, Fluids & Plasmas
D. Eldon, H. Anand, J-G Bak, J. Barr, S-H Hahn, J. H. Jeong, H-S Kim, H. H. Lee, A. W. Leonard, B. Sammuli, G. W. Shin, H. Q. Wang
Summary: Detachment control based on ion saturation current I-sat measurements has been implemented in the KSTAR tokamak, allowing for accurate tracking of target trajectories and adaptability to changing scenarios.
PLASMA PHYSICS AND CONTROLLED FUSION
(2022)
Article
Physics, Fluids & Plasmas
J. Kim, J. Kang, T. Rhee, J. Jo, H. Han, M. Podesta, J. H. Lee, S. Lee, J. G. Bak, M. J. Choi, R. Nazikian, H. Jhang, J. Ko, M. Joung, Y-M Jeon, Y-S Na, K. Shinohara, C. Z. Cheng
Summary: Recent experiments have shown that electron cyclotron current drive (ECCD) can suppress Alfvenic activity, enhance the confinement of fast ions, and improve the performance of fusion plasmas.
Article
Physics, Fluids & Plasmas
Sang-Min Byun, Yong-Su Na, Sang-Jun Lee, Min-Ki Jung, Kyoung-Jae Chung, Y. S. Hwang, Deok-Kyu Kim, Sang June Hahn
Summary: This paper investigates the wire X-pinch (WXP) evolutions using the Eulerian resistive magneto-hydrodynamic code, STHENO, on 2D/3D geometry. It applies a single-fluid two-temperature model to describe pinch plasmas in local thermal equilibrium. The results show that the micrometer-size plasma column is elongated axially with the onset of the neck cascading structure. The radiation power calculated from simulations matches the measured x-ray power. Additionally, 3D analyses reveal that the current density, rather than the line density, determines the central pinching condition, and multiple plasma instabilities degrade the radiation performance on small cross-angle WXPs.
PHYSICS OF PLASMAS
(2022)
Article
Physics, Fluids & Plasmas
D. Eldon, H. Anand, J-G Bak, J. Barr, S-H Hahn, J. H. Jeong, H-S Kim, H. H. Lee, A. W. Leonard, B. Sammuli, G. W. Shin, H. Q. Wang
Summary: Detachment control based on ion saturation current I-sat measurements has been implemented in the KSTAR tokamak, allowing for accurate tracking of target trajectories and adaptability to changing scenarios.
PLASMA PHYSICS AND CONTROLLED FUSION
(2022)
Article
Physics, Multidisciplinary
Chan-Young Lee, SeongCheol Kim, Young-Gi Kim, YooSung Kim, Kihyun Lee, Y. S. Hwang, Yong-Su Na
Summary: The predictive modeling of the VEST device is presented in this paper. A integrated simulation tool was used for conducting 1D transport simulation considering neoclassical and turbulent transport, and pre-fill gas neutrals. A set of predictive simulations were conducted by varying pre-fill gas levels. The electron density, electron and ion temperatures were then compared with the simulation results.
JOURNAL OF THE KOREAN PHYSICAL SOCIETY
(2022)
Article
Multidisciplinary Sciences
H. Han, S. J. Park, C. Sung, J. Kang, Y. H. Lee, J. Chung, T. S. Hahm, B. Kim, J-K Park, J. G. Bak, M. S. Cha, G. J. Choi, M. J. Choi, J. Gwak, S. H. Hahn, J. Jang, K. C. Lee, J. H. Kim, S. K. Kim, W. C. Kim, J. Ko, W. H. Ko, C. Y. Lee, J. H. Lee, J. K. Lee, J. P. Lee, K. D. Lee, Y. S. Park, J. Seo, S. M. Yang, S. W. Yoon, Y-S Na
Summary: Nuclear fusion is a promising alternative energy source, but there are still many scientific challenges to harnessing fusion energy on a large scale. Researchers have achieved a plasma fusion regime at the Korea Superconducting Tokamak Advanced Research facility that meets most of the requirements for sustainable fusion. By stabilizing core plasma turbulence with abundant fast ions, they were able to generate plasma at a temperature of 100 million kelvin, lasting up to 20 seconds without instabilities or impurity accumulation. This regime, characterized by low plasma density and moderate input power, shows promise for reliable and disruption-free sustained operation, making it a potential path towards commercial fusion reactors.
Article
Physics, Fluids & Plasmas
J. Y. Kim, H. S. Han
Summary: High triangularity may lead to issues with access to the H-mode pedestal, potentially due to an increase in magnetic shear, which could also be the cause of triggering the wide pedestal quiescent-H mode with broadband fluctuations.
Article
Physics, Fluids & Plasmas
J. Y. Kim, H. S. Han, L. Jung
Summary: Based on a heuristic model of the SOL plasma dynamics, a new type of limit-cycle-oscillation (LCO) is shown to be possible in the SOL region. The positive feedback amplification of the SOL radial electric field through the SOL turbulence suppression and temperature profile steepening is the key trigger process. This SOL-LCO can cause oscillation motion in the edge plasma inside the separatrix, with features qualitatively similar to those observed in recent experiments.
Article
Nuclear Science & Technology
Jun-Gyo Bak, Heung-Su Kim, Sang-Hee Hahn, Jayhyun Kim, Jeong-Won Lee, KSTAR Team
Summary: This study investigates the toroidal eddy current during plasma disruptions in the KSTAR tokamak using discrete and continuous Rogowski coil measurements. The results show a linear correlation between the eddy current and plasma current, but a weak dependence on the current quench rate. The eddy current decays faster in the inner part compared to the outer part, and the outer part is verified by comparing it with direct measurements at the gap resistors. During vertical displacement events, a counter-Ip direction eddy current is always detected, and its maximum value correlates linearly with the vertical growth rate.
FUSION ENGINEERING AND DESIGN
(2023)
Article
Physics, Multidisciplinary
Jeongwon Lee, Hyun-Tae Kim, Jayhyun Kim, Sang-hee Hahn, June-Woo Juhn, JuHyuk Jang, Jun-Gyo Bak, SooHyun Son, Mi Jung, YoungHwa An, Yong-Su Na, Si-Woo Yoon
Summary: An electron cyclotron heating (ECH) power absorption model, DYON-EC, was developed and validated against KSTAR ECH-assist start-up experiments. The absorbed ECH power was calculated based on electron density, temperature, and hardware settings, with consideration of wave parameter changes due to wall reflection. The DYON-EC model successfully reproduced multiple KSTAR EC-assisted discharges using optimized simulation settings, confirming its validity.
Article
Physics, Fluids & Plasmas
J. Y. Kim, H. S. Han, S. K. Kim
Summary: In plasmas with strong shape and large pedestal width, the eigenvalue spectrum of the peeling ballooning mode (PBM) shifts to the low-n regime near one as the normalized beta (beta(N)) increases. This shift smoothly connects the PBM to the external kink mode (EKM) at n = 1. The mode stability becomes sensitive to both the local pedestal gradient and global beta, allowing for an anti-correlation between the two driving forces.
PHYSICS OF PLASMAS
(2023)
Article
Nuclear Science & Technology
Hyunsun Han, June-woo Juhn, Mi Joung, Yong Un Nam, Byungken Na, Jong-Gu Kwak, Jinseok Ko, Sang-Hee Hahn, Giwook Shin, Jeongwon Lee, Young-Mu Jeon, Kyu-Dong Lee, Jong-Ha Lee, Jinhyun Jeong, Hyunseok Kim, Min-ho Woo, Jayhyun Kim, Sonjong Wang, Won-Ha Ko, Woong Chae Kim, Si-Woo Yoon
Summary: At the beginning of every KSTAR campaign, a stable tokamak plasma operation condition is aimed to be established through confirming the plasma startup recipe and checking auxiliary devices. A robust plasma startup scenario is secured for all plasma experiments, followed by plasma shaping and testing of fueling and heating devices. The radial profile diagnostics are tested by moving the plasma boundary and varying the operating toroidal magnetic field. This paper explains the detailed routine process for plasma commissioning in the KSTAR campaign.
FUSION ENGINEERING AND DESIGN
(2023)
Article
Physics, Fluids & Plasmas
Minwoo Kim, G. Shin, J. Lee, W. H. Ko, H. Han, S. -H. Hahn, S. K. Kim, S. M. Yang, R. Shousha, H. S. Kim, J. -W. Juhn, G. Y. Park, E. Kolemen
Summary: The study introduces the integrated Resonant Magnetic Perturbation (RMP)-based Edge-Localized Mode (ELM)-crash-control process to enhance plasma performance and minimize confinement degradation caused by RMP. The process incorporates the latest achievements in RMP technique and uses real-time Machine Learning (ML) classifier to trigger the onset of Edge-localized RMP (ERMP) at the L-H transition timing. The integrated process achieves significant beta(N) enhancement during the suppression phase and demonstrates quicker restoration compared to the conventional RMP method.
Article
Physics, Fluids & Plasmas
Youngho Lee, S. K. Kim, J. W. Kim, B. Kim, M. S. Park, J. M. Kwon, M. J. Choi, S. H. Hahn, M. W. Lee, S. M. Yang, S. C. Hong, C. Y. Lee, S. J. Park, C. S. Byun, H. -s. Kim, J. Chung, Yong-Su Na
Summary: This paper investigates the origins and trigger mechanisms responsible for performance enhancements observed in hybrid scenario experiments conducted in KSTAR. The study finds that the broadening and increased density in the pedestal formation, as well as the increase in fast ion pressure, significantly contribute to the performance improvement. The presence of Coherent Edge-localized Mode (CEM) activity is also found to be related to performance enhancement.
Article
Physics, Fluids & Plasmas
T. S. Hahm, G. J. Choi, S. J. Park, Y. -S. Na
Summary: In this study, the effects of fast ions on turbulence-driven zonal flow generation were investigated using a simple reduced model based on the Hasegawa-Mima equation. The higher characteristic frequency of parallel motion of fast ions compared to the phase velocity of drift waves along the magnetic field allowed for derivation of the reduced model equations. Analysis of nonlinear mode coupling showed that the threshold amplitude of drift waves required for zonal flow modulational instability was significantly reduced, making its generation easier. This finding suggests a common nonlinear physics mechanism underlying recent results on tokamak plasma confinement enhancement caused by fast ions.
PHYSICS OF PLASMAS
(2023)
