Article
Physics, Fluids & Plasmas
J. Ortiz, J. Varela, D. A. Spong, L. Garcia, Y. Ghai
Summary: The aim of this study is to analyze the linear stability of Alfven eigenmodes (AE) in the QPS device heated by a tangential neutral beam injector (NBI). The analysis is performed for different operational regimes of the NBI, including EP beta, EP energy, and radial location of the beam. The stability of AE is improved in simulations with finite beta equilibria and three period configurations.
Article
Physics, Fluids & Plasmas
J. Varela, D. A. Spong, Y. Todo, L. Garcia, Y. Ghai, J. Ortiz, R. Seki
Summary: The aim of this study is to analyze the saturation regime of the toroidal Alfven eigenmodes (TAE) in the Large Helical Device plasma, especially the MHD burst. The study uses numerical simulations to show that different modes of TAE can interact and become unstable, leading to MHD burst and significant effects on plasma properties.
Article
Physics, Fluids & Plasmas
J. Varela, A. Shimizu, D. A. Spong, L. Garcia, Y. Ghai
Summary: This study aims to analyze the stability of Alfven eigenmodes in the Chinese First Quasi-axisymmetric Stellarator. Simulation results show that different types of AEs become unstable due to the slowing down process of EP, with the energy level of EP affecting the stability. Increase in thermal plasma density improves AE stability in the plasma.
Article
Physics, Fluids & Plasmas
J. Varela, D. A. Spong, L. Garcia, S. Ohdachi, K. Y. Watanabe, R. Seki, Y. Ghai
Summary: The study aimed to analyze the saturation regime of the energetic ion-driven resistive interchange mode in LHD plasma. Nonlinear simulations were conducted to reproduce the experimental observations of 1/1 EIC saturation phases, showing enhancement of the resistive interchange modes as EP beta increases and triggering burst events. The study also revealed inward propagation and stabilization phases of the 1/1 EIC due to the nonlinear destabilization of energetic particle modes.
Article
Physics, Fluids & Plasmas
Hao Wang, Yasushi Todo, Jie Huang, Yasuhiro Suzuki, Akihiro Shimizu, Kunihiro Ogawa, Xianqu Wang, Panith Adulsiriswad
Summary: A nonlinear simulation of energetic particle driven instabilities in the Chinese First Quasi-axisymmetric Stellarator (CFQS) was conducted for the first time. The study found energetic-particle modes and toroidal Alfven eigenmodes, and confirmed resonance conditions and nonlinear frequency chirping.
Article
Physics, Fluids & Plasmas
Samuel A. Lazerson, David Pfefferle, Michael Drevlak, Hakan Smith, Joachim Geiger, Simppa Akaslompolo, Pavlos Xanthopoulos, Andreas Dinklage, Oliver Ford, Paul McNeely, Norbert Rust, Sergey Bozhenkov, Dirk Hartmann, Kian Rahbarnia, Tamara Andreeva, Jonathan Schilling, Christian Brandt, Ulrich Neuner, Henning Thomsen, Robert C. Wolf
Summary: The study compares an energetic particle slowing down model in the BEAMS3D stellarator neutral beam code with analytic models and experimental data from the Wendelstein 7-X experiment. Validation of neutral beam deposition codes was achieved through recent neutral beam experiments in W7-X. The research demonstrates that neutral beam current drive dominates over bootstrap current, resulting in a reversal of the toroidal current, and density peaking can destabilize electron turbulence in the discharge.
Article
Physics, Fluids & Plasmas
J. Varela, D. A. Spong, L. Garcia, Y. Ghai, D. Zarzoso, D. del-Castillo-Negrete, H. Betar, J. Ortiz, D. C. Pace, M. A. Van Zeeland, X. Du, R. Sanchez, V Tribaldos, J. M. Reynolds-Barredo
Summary: This study analyzes the effect of the neutral beam injector (NBI) operation regime on the saturation phase of the Alfven Eigenmodes (AEs) in DIII-D plasma. The analysis suggests a transition from the soft MHD to the hard MHD limit if the simulation EP beta > 0.02, leading to bursting MHD activity caused by radial AEs overlapping. Simulations in the hard MHD regime show a decrease of the AE frequency in the saturation phase.
PLASMA PHYSICS AND CONTROLLED FUSION
(2023)
Article
Physics, Fluids & Plasmas
Yueyan Li, Matteo Valerio Falessi, Philipp Lauber, Yang Li, Zhiyong Qiu, Guangyu Wei, Fulvio Zonca
Summary: Shear Alfven wave (SAW)/drift Alfven wave (DAW) fluctuations can be destabilized by energetic particles (EPs) and thermal plasma components, influencing energy and momentum transport in fusion plasmas. The drift Alfven energetic particle stability (DAEPS) code is a finite element eigenvalue code used to analyze EP-excited Alfven instabilities. The code provides frequency, growth/damping rate, parallel mode structure, and asymptotic behavior, describing fluid and kinetic spectra as well as stable and unstable modes. The model equations have been extended to include general axisymmetric geometry and the response of circulating and trapped particles. This work discusses the linear dispersion relation and parallel mode structure of DAEPS-computed drift Alfven instabilities, and uses the Dyson-Schrodinger model to analyze EP energy and momentum flux.
PLASMA PHYSICS AND CONTROLLED FUSION
(2023)
Article
Physics, Fluids & Plasmas
Alexandra LeViness, John C. C. Schmitt, Samuel A. A. Lazerson, Aaron Bader, Benjamin J. J. Faber, Kenneth C. C. Hammond, David A. A. Gates
Summary: The goal of this work was to optimize stellarator equilibrium for good confinement of energetic particles. This was achieved by minimizing deviations from quasi-axisymmetry and reducing the angle between magnetic flux surfaces and contours of the second adiabatic invariant. Multiple optimizations resulted in equilibria with significantly reduced energetic particle losses, as evaluated by Monte Carlo simulations.
Article
Physics, Fluids & Plasmas
P. Adulsiriswad, Y. Todo, S. Kado, S. Yamamoto, S. Kobayashi, S. Ohshima, H. Okada, T. Minami, Y. Nakamura, A. Ishizawa, S. Konoshima, T. Mizuuchi, K. Nagasaki
Summary: The study investigates the interaction between energetic particles and EP-driven MHD instabilities in Heliotron J using the MEGA simulation code with free boundary conditions. It is found that the free boundary conditions affect the spatial profile of modes, while under fixed boundary conditions, the linear growth rate of EP-driven MHD modes with low mode numbers is underestimated. The strongest interactions between EP and experimentally-observed modes occur in the high-velocity region.
Article
Physics, Fluids & Plasmas
Baofeng Gao, Huishan Cai, Feng Wang, Xiang Gao, Yuanxi Wan
Summary: The study found that trapped energetic ions can stabilize the double tearing mode for low energetic-ion beta, but excite the fishbone-like mode when the beta exceeds a certain threshold. The threshold increases with resistivity, and the presence of resistivity reduces the growth rate of the fishbone-like mode.
PHYSICS OF PLASMAS
(2021)
Article
Physics, Fluids & Plasmas
Baofeng Gao, Huishan Cai, Xiang Gao, Yuanxi Wan
Summary: The influence of circulating energetic ions (CEIs) on double tearing mode (DTM) was studied using a global kinetic-MHD hybrid simulation. It was found that CEIs with small orbit width destabilize the DTM, but their destabilizing effect decreases as the orbit width increases. When the orbit width is large enough, the DTM transitions to single tearing modes, making the mode more stable.
Article
Physics, Fluids & Plasmas
Haifeng Liu, Akihiro Shimizu, Yuhong Xu, Shoichi Okamura, Shigeyoshi Kinoshita, Mitsutaka Isobe, Yangbo Li, Guozheng Xiong, Xianqu Wang, Jie Huang, Jun Cheng, Hai Liu, Xin Zhang, Dapeng Yin, Y. Wang, Takanori Murase, Sho Nakagawa, Changjian Tang
Summary: CFQS is the first operational quasi-axially symmetric stellarator in the world, aiming to achieve the canonical quasi-axisymmetric configuration experimentally. It has advanced features, compact design, and high pressure stability.
Article
Instruments & Instrumentation
A. Iwata, S. Kado, M. Murakumo, T. Shikama, G. Motojima, A. Mori, C. Feng, H. Okada, T. Minami, S. Ohshima, S. Kobayashi, A. Ishizawa, Y. Nakamura, S. Konoshima, T. Mizuuchi, K. Nagasaki
Summary: This study evaluated the application of the Pa-alpha line in the near-infrared region for measuring the electron density of small-pellet ablation cloud in Heliotron J. The results showed that the Pa-alpha line is three-to-four times broader than the visible H-beta line for the same electron density. Preliminary experiments using a portable NIR spectrometer determined the marginal density below which the broadening was undetectable, and suggested methods to decrease the lower detection density limit.
REVIEW OF SCIENTIFIC INSTRUMENTS
(2022)
Article
Physics, Fluids & Plasmas
Y. Yamamoto, S. Murakami, C. C. Chang, S. T. A. Kumar, J. N. Talmadge, K. M. Likin, D. T. Anderson
Summary: This study observes the spontaneous plasma flows in electron cyclotron heating plasmas and evaluates the parallel flow driven by ECH force. The obtained results show reasonable agreement with experiments, indicating that the radial electron current generated by ECH could drive the parallel flow.
Article
Physics, Fluids & Plasmas
B. Ph van Milligen, I Voldiner, B. A. Carreras, L. Garcia, M. A. Ochando
Summary: In this study, we measured turbulent quantities inside the plasma edge in the TJ-II stellarator using a Langmuir probe during rotational transform scans. We found that the poloidal plasma velocity and radial electric field have a radial structure that relates to the rotational transform profile and lowest order rational surfaces. The particle flux and flow shear suppression term also exhibit a radial pattern, but their relation to the low-order rational surfaces is less clear. The results suggest the presence of an unknown term, the instability growth rate, in the turbulence evolution equation.
Article
Astronomy & Astrophysics
J. Varela, F. Pantellini
Summary: The aim of this study was to identify the solar wind conditions required for the formation of slow-mode structures (SMS) in the Mercury magnetosphere by comparing MESSENGER magnetometer data and magnetohydrodynamics simulations. The results showed that optimal wind conditions for SMS formation require that the interplanetary magnetic field is oriented in the northward or radial directions. MESSENGER magnetometer data provided indirect evidence of SMS by showing a significant decrease in the magnetic field module after the satellite crossed nearby the observed compression front in the simulation.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Physics, Fluids & Plasmas
S. Mulas, A. Cappa, J. Martinez-Fernandez, D. Lopez Bruna, J. L. Velasco, T. Estrada, J. M. Gomez-Manchon, M. Liniers, K. J. McCarthy, I. Pastor, F. Medina, E. Ascasibar
Summary: In this paper, the results of neutral-beam current drive (NBCD) experiments in the TJ-II stellarator are analyzed to validate the theoretical predictions. Both parallel and anti-parallel injection with respect to the magnetic field were explored using different injected beam power and plasma densities. The simulation and analysis show good agreement with the measured toroidal current in NBI2 plasmas, but the current driven by NBI1 is significantly lower than predicted, possibly due to increased lithium presence in the plasma.
Article
Physics, Fluids & Plasmas
Junli Zhang, Zhifeng Cheng, Yanli Peng, Zhoujun Yang, Kazunobu Nagasaki, Nengchao Wang, Hao Cai, Yonghua Ding, Zhipeng Chen, Zhongyong Chen, Wei Jiang, Donghui Xia, Zhijiang Wang, Yuan Pan
Summary: The EDI system has been developed and utilized for start-up studies on J-TEXT tokamak. The pre-ionization effect of EDI on start-up was verified through a breakdown experiment, and a 0D model was developed to quantitatively explain this effect. The comparison between experiment and simulation showed that EDI-assisted start-up resulted in improved ionization and smoother rise in energy.
Article
Physics, Fluids & Plasmas
Junli Zhang, Peter C. de Vries, Kazunobu Nagasaki, Donghui Xia, Wei Jiang, Zhoujun Yang, Zhifeng Cheng, Li Gao, Xin Xu, Zhijiang Wang, Nengchao Wang, Yonghua Ding, Zhipeng Chen, Zhongyong Chen, Yuan Pan, J-TEXT Team
Summary: The minimum ECH power requirements for second harmonic X-mode (X2 mode) electron cyclotron heating (ECH) assisted start-up were investigated on the J-TEXT device. It was found that injecting 300 kW of X2-mode ECH power can ensure robust breakdown, with a critical ECH power of approximately 200 kW for successful start-up. The effects of varying ECH power, pulse-width, and toroidal magnetic field on start-up were also studied, showing that higher ECH power leads to quicker and stronger ionization, and higher pre-plasma density can decrease the required toroidal electric field for breakdown, while enhanced CIII emission may not be beneficial for start-up. The transition from ECH plasma to ohmic plasma suggests a modification of the purely ohmic breakdown process.
Article
Physics, Fluids & Plasmas
J. Ortiz, J. Varela, D. A. Spong, L. Garcia, Y. Ghai
Summary: The aim of this study is to analyze the linear stability of Alfven eigenmodes (AE) in the QPS device heated by a tangential neutral beam injector (NBI). The analysis is performed for different operational regimes of the NBI, including EP beta, EP energy, and radial location of the beam. The stability of AE is improved in simulations with finite beta equilibria and three period configurations.
Article
Astronomy & Astrophysics
J. Varela, A. S. Brun, A. Strugarek, V Reville, P. Zarka, F. Pantellini
Summary: This study analyzes the Earth's habitability, taking into account the direct impact of the solar wind on the Earth's atmosphere. It finds that the solar wind can significantly affect the habitability of the Earth.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Physics, Fluids & Plasmas
L. Garcia, I. Garcia-Cortes, B. A. Carreras, K. J. Mccarthy, B. Ph. van Milligen
Summary: The improvement in confinement associated with the injection of pellets has been observed in TJ-II and other devices. A simple model is used to study the modification of turbulent transport by pellet injection and its effect on particle confinement time. The analysis of the results shows the relationship between the confinement improvement and the evolution of shear flow due to turbulence, particularly near low order rational surfaces.
PHYSICS OF PLASMAS
(2023)
Article
Physics, Fluids & Plasmas
J. Varela, D. A. Spong, L. Garcia, Y. Ghai, D. Zarzoso, D. del-Castillo-Negrete, H. Betar, J. Ortiz, D. C. Pace, M. A. Van Zeeland, X. Du, R. Sanchez, V Tribaldos, J. M. Reynolds-Barredo
Summary: This study analyzes the effect of the neutral beam injector (NBI) operation regime on the saturation phase of the Alfven Eigenmodes (AEs) in DIII-D plasma. The analysis suggests a transition from the soft MHD to the hard MHD limit if the simulation EP beta > 0.02, leading to bursting MHD activity caused by radial AEs overlapping. Simulations in the hard MHD regime show a decrease of the AE frequency in the saturation phase.
PLASMA PHYSICS AND CONTROLLED FUSION
(2023)
Article
Astronomy & Astrophysics
Ruchi Mishra, Miljenko Cemeljic, Jacobo Varela, Maurizio Falanga
Summary: The first extrasolar planets were accidentally discovered by detecting slight variations in the pulsar timing. Based on this, auroras on planets around millisecond pulsars are predicted. The radio emission from such planetary auroras could be observed using current instruments. In addition to studying extreme atmospheric conditions, the detection also provides an opportunity to probe the pulsar wind directly.
ASTROPHYSICAL JOURNAL LETTERS
(2023)
Article
Physics, Fluids & Plasmas
F. Kin, S. Inagaki, K. Nagasaki, M. Luo, T. Minami, S. Ohshima, S. Kobayashi, S. Kado, S. Konoshima, T. Mizuuchi, N. Marushchenko
Summary: This study observes avalanche-like electron thermal transport in Heliotron J and identifies the characteristics and propagation of temperature fluctuations associated with these avalanches.
PHYSICS OF PLASMAS
(2023)
