Experiments are reported where a collisionfree plasma cloud penetrates a magnetic barrier by self-polarization. We here focus on the resulting anomalous magnetic field diffusion into the plasma cloud, two orders of magnitude faster than classical, which is one important aspect of the plasma cloud penetration mechanism. Without such fast magnetic diffusion, clouds with kinetic beta below unity would not be able to penetrate magnetic barriers at all. Tailor-made diagnostics has been used for measurements in the parameter range with the kinetic beta ? 0.5 to 10, and with normalized width w/r(gi) of the order of unity. Experimental data on hf fluctuations in density and in electric field has been combined to yield the effective anomalous transverse resistivity eta(EFF). It is concluded that they are both dominated by highly nonlinear oscillations in the lower hybrid range, driven by a strong diamagnetic current loop that is set up in the plasma in the penetration process. The anomalous magnetic diffusion rate, calculated from the resistivity eta(EFF), is consistent with single-shot multi-probe array measurements of the diamagnetic cavity and the associated quasi-dc electric structure. An interpretation of the instability measurements in terms of the resistive term in the generalized (low frequency) Ohm's law is given.
It is shown that the penetration of an oscillating electric field in a semi-infinite classical plasma obeys the standard exponential attenuation law $e^{-x/λ_{e}}$ (besides oscillations), where $x$ is the distance from the wall and $λ_{e}$ is the extinction length (penetration depth, attenuation length). The penetration depth is computed here explicitly; it is shown that it is of the order $λ_e \simeq [\mid\varepsilon \mid/(1-\varepsilon)]^{1/3}v_{th} / ω$, where $\varepsilon$ is the dielectric function, $ω$ is the frequency of the field and $v_{th}=\sqrt{T/m}$ is the thermal velocity ($T$ bei…
The penetration of a supersonic particle at the interface was studied in a binary complex plasma. Inspired by the experiments performed in the PK-3 Plus Laboratory on board the International Space Station, Langevin dynamics simulations were carried out. The evolution of Mach cone at the interface was observed, where a kink of the lateral wake front was observed at the interface. By comparing the evolution of axial and radial velocity, we show that the interface solitary wave is non-linear. The dependence of the background particle dynamics in the vicinity of the interface on the penetration di…
Recent observations of the successive formations of the 4=1; 3=1, and 2=1 magnetic islands as well as the subsequent braking of the 2=1 mode during a low-Z impurity penetration process in EAST experiments are well reproduced in our 3D resistive MHD simulations. The enhanced parallel current perturbation induced by impurity radiation predominately contributes to the tearing mode growth, and the 2=1 island rotation is mainly damped by the impurity accumulation as results of the influence from high n modes.
Improved n=1 Empirical Error Field Penetration Threshold Scaling with Ohmic and L-Mode Conventional Tokamak Plasma Discharges
Columbia University（哥伦比亚大学）；Seoul National University（首尔大学）；Institute of Plasma Physics Chinese Academy of Sciences（中国科学院等离子体物理研究所）；Huazhong University of Science and Technology（华中科技大学）；General Atomics（通用原子公司）；Consorzio RFX (CNR, ENEA, INFN, Universitá di Padova, Acciaierie Venete SpA)（RFX联合体（意大利国家研究委员会、国家新能源与可再生能源署、意大利国家核物理研究所、帕多瓦大学、威尼斯钢铁公司））；University of Padova（帕多瓦大学）；UKAEA, Culham Campus（英国原子能管理局，库姆校区）
Screening effect of plasma flow on the resonant magnetic perturbation penetration in tokamak based on two-fluid model
Key Laboratory of Materials Modification by Laser, Ion, and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology（大连理工大学物理学院激光、离子和电子束材料改性教育部重点实验室）；Key Laboratory of Geospace Environment, University of Science and Technology of China（中国科学技术大学空间环境重点实验室）；Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology（大连理工大学电子信息与电气工程学部）
Penetration Deep into Tissues of Reactive Oxygen Species Generated in Floating-Electrode Dielectric Barrier Discharge (FE-DBD): in Vitro Agarose Gel Model Mimicking an Open Wound
Edge-Localized-Mode (ELM) suppression by resonant magnetic perturbations (RMPs) generally occurs over very narrow ranges of the plasma current (or magnetic safety factor q95) in the DIII-D tokamak. However, wide q95 ranges of ELM suppression are needed for the safety and operational flexibility of ITER and future reactors. In DIII-D ITER Similar Shape (ISS) plasmas with n=3 RMPs, the range of q95 for ELM suppression is found to increase with decreasing electron density. Nonlinear two-fluid MHD simulations reproduce the observed q95 windows of ELM suppression and the dependence on plasma densit…
For the first time the pellet cycle of a multiple-isotope plasma is successfully reproduced with reduced turbulent transport modelling, within an integrated simulation framework. Future nuclear fusion reactors are likely to be fuelled by cryogenic pellet injection, due to higher penetration and faster response times. Accurate pellet cycle modelling is crucial to assess fuelling efficiency and burn control. In recent JET tokamak experiments, deuterium pellets with reactor-relevant deposition characteristics were injected into a pure hydrogen plasma. Measurements of the isotope ratio profile inf…
We study the penetration of ultraintense circularly polarized laser pulses into a thick subcritical plasma layer with accounting for radiation friction. We show that radiation pressure is enhanced by radiation friction in the direction transverse to the laser pulse propagation, and that for stronger and longer laser pulses this mechanism dominates over the ordinary ponderomotive pressure, thus resulting in a stronger charge separation than anticipated previously. We give estimates of the effect and compare them with the results of 1D and 2D PIC simulations.
In magnetized plasma situations where magnetic fields intersect massive conducting boundaries, "line-tied" boundary conditions are often used, analytically and in numerical simulations. For ideal MHD plasmas, these conditions are arrived at given the relatively long time scales for magnetic fields penetrating resistively into good conductors. Under line-tied boundary conditions, numerical simulations often exhibit what could be construed as numerical "noise" emanating from the boundaries. We show here that this "noise" is real. By combining numerical and analytical methods, we highlight the ex…
A detailed understanding of island seeding is crucial to avoid (N)TMs and their negative consequences like confinement degradation and disruptions. In the present work, we investigate the growth of 2/1 islands in response to magnetic perturbations. Although we use externally applied perturbations produced by resonant magnetic perturbation (RMP) coils for this study, results are directly transferable to island seeding by other MHD instabilities creating a resonant magnetic field component at the rational surface. Experimental results for 2/1 island penetration from ASDEX Upgrade are presented e…
In-depth diffusion of oxygen into LDPE exposed to an Ar--O2 atmospheric post-discharge: a complementary approach between AR-XPS and Tof-SIMS techniques
Due to the complicated environment of the plasma sheath, it is difficult to experimentally measure plasma characteristics in the narrow geometry where sheaths from opposite boundaries overlap. Since such geometries are often found in industrial plasma applications, accurate measurements of this type are of significant interests. In this paper, we employ micron-sized dust grains as non-perturbative probes of the plasma environment. A particle-freefall technique is then used to measure the sheath profiles produced by a rf plasma within a glass box. The results show that this technique can identi…
We present that a statistical method known as the Complexity-Entropy analysis is useful to characterize a state of plasma turbulence and flux in the resonant magnetic perturbation (RMP) edge localized mode (ELM) control experiment. The RMP ELM suppression phase with the stochastic pedestal top temperature fluctuation can be distinguished from the natural ELM free phase with the chaotic fluctuation. It is discussed that the stochastic temperature fluctuation localized near the pedestal top can be originated from the narrow layer of the field penetration near the pedestal top. The forced magneti…
We demonstrate by computer simulations, laser plasma experiments, and analytic theory that a hitherto unknown instability is excited in the beam plasma system with finite transverse size. This instability is responsible for the generation of magnetic fields at scales comparable to the transverse beam dimension which can be much longer than the electron skin depth scale. This counterintuitive result arises due to radiative leakage associated with finite beam boundaries which are absent in conventional infinite periodic systems considered in earlier simulations as well as theoretical analyses an…
Turbulent plasmas notably self-organize to higher energy states upon application of additional free energy sources or modification of edge operating conditions. Mechanisms whereby such bifurcations occur have been actively debated for decades. Enhanced confinement occurs at the plasma edge, where a shortfall of predicted turbulence intensity has been puzzling scientists for decades. We show, from the primitive kinetic equations that both problems are connected and that interplay of confined plasma turbulence with its material boundaries is essential to curing the shortfall of predicted turbule…
Plasma response to resonant magnetic perturbations (RMPs) near the pedestal top is crucial for accessing edge localized modes (ELMs) suppression in tokamaks. Since radial location of rotation zero-crossing plays a key role in determining the threshold for field penetration of RMP, plasma response may be different in low input torque plasmas. In this work, the linear MHD code MARS-F is applied to reveal the dependence of plasma response to RMP on rotation zero-crossing by a scan of rotation profiles based on an EAST equilibrium. It is shown that the plasma response is enhanced when zero-crossin…
The Role of Phase and Spatial Modes in Wave-Induced Plasma Transport
Institute of Physics, University of São Paulo（圣保罗大学物理研究所）；Aix-Marseille Université, CNRS, UMR 7345 PIIM（艾克斯-马赛大学，法国国家科学研究中心，UMR 7345 PIIM）；Department of Statistics, Applied Mathematics and Computer Science, São Paulo State University（圣保罗州立大学统计、应用数学与计算机科学系）
This paper presents the plasma potential distribution across magnetic field lines in an argon/oxygen plasma created by 13.56 MHz CCRF discharge consisting of a pair of ring electrodes. It is found that the radial plasma density, electron temperature, and plasma potential shows unusual trends as the magnetic field strength and gas pressure increase. An analytical model has been formulated to explain the radial plasma potential profile when the short-circuiting effect due to conducting boundaries can be neglected. It is found that with certain approximations, the plasma potential distribution ca…
