Experimental investigation of kinetic instabilities driven by runaway electrons in the EXL-50 spherical torus

In this study, the first observation of high-frequency instabilities driven by runaway electrons has been reported in the EXL-50 spherical torus using a high-frequency magnetic pickup coil. The central frequency of these instabilities is found to be exponentially dependent on the plasma density, similar to the dispersion relation of the whistler wave. The instability frequency displays chirping characteristics consistent with the Berk-Breizman model of beam instability. Theoretically, the excitation threshold of the instability driven by runaway electrons is related to the ratio of the runaway electron density to the background plasma density, and such a relationship is first demonstrated experimentally in this study. The instability can be stabilized by increasing the plasma density, consistent with the wave-particle resonance mechanism. This investigation demonstrates the controlled excitation of chirping instabilities in a tokamak plasma and reveals new features of these instabilities, thereby advancing the understanding of the mechanisms for controlling and mitigating runaway electrons

Observation of whistler wave instability driven by temperature anisotropy of energetic electrons on EXL-50 spherical torus

Electromagnetic modes in the frequency range of 30-120MHz were observed in electron cyclotron wave (ECW) steady state plasmas on the ENN XuanLong-50 (EXL-50) spherical torus. These modes were found to have multiple bands of frequencies proportional to the Alfv\'en velocity. This indicates that the observed mode frequencies satisfy the dispersion relation of whistler waves. In addition, suppression of the whistler waves by the synergistic effect of Lower Hybrid Wave (LHW) and ECW was also observed. This suggests that the whistler waves were driven by temperature anisotropy of energetic electrons. These are the first such observations (not runaway discharge) made in magnetically confined toroidal plasmas and may have important implications for studying wave-particle interactions, RF wave current driver, and runaway electron control in future fusion devices

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors without a central solenoid. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to improve current drive effectiveness. Copious energetic electrons are produced and measured with hard X-ray detectors, carry the bulk of the plasma current ranging from 50kA to 150kA, which is maintained for more than 1s duration. It is observed that over one Ampere current can be maintained per Watt of ECRH power issued from the 28-GHz gyrotrons. The plasma current reaches Ip>80kA for high density (>5e18me-2) discharge with 150kW ECHR heating. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits of energetic electrons, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates smaller closed magnetic-flux surfaces of low aspect ratio that in turn confine the thermal plasma electrons and ions and participate in maintaining the equilibrium force-balance

Design and Research of Electron Cyclotron Resonance Heating and Current Dive System on HL-2M Tokamak

A research has been conducted to develop an 8MW electron cyclotron resonance heating and current drive (ECRH/ECCD) system on HL-2M tokamak. The ECRH system compromise eight 1MW gyrotrons, eight evacuated transmission lines and three launchers. The main purpose of the ECRH system was to suppress the neo-classical tearing modes and control the plasma profile. This paper presents an overview of the design and studies performed in this framework. Some primary test results of the critical components have been released in this paper, e.g. polarizers, power monitor and fast steering launchers

Protocol for a Single-Center Randomized Controlled Trial of Percutaneous Coronary Intervention Via Distal Transradial Access Versus Transradial Access

Background: Although transradial access (TRA) has become the main vascular access for coronary intervention, its high radial artery occlusion rate limits its application in some patients. Studies have shown that compared with TRA, distal transradial access (dTRA) with the snuffbox area or the Hegu acupoint area as the puncture point significantly decreases the incidence of radial artery occlusion. However, no randomized controlled study has confirmed the safety and efficacy of coronary artery intervention via dTRA in China. Methods and analyses: This single-center, prospective, randomized controlled, superiority open-label study will enroll 428 consecutive patients with coronary heart disease undergoing percutaneous coronary intervention as the study population. After preoperative evaluation, the participants will be randomly divided into a study group (dTRA) and control group (TRA) in a 1:1 ratio. The primary endpoint (radial artery occlusion at 24 hours after operation) and secondary endpoint events will be evaluated and recorded. Study registration: This study has been registered in the Chinese Clinical Trial Registry (registration number: ChiCTR2300073902)

Etude du transport de la chaleur et des particules dans les tokamaks Tore Supra et HL-2A

Le transport de la chaleur et des particules est un des sujets de recherche fondamentaux de la physique des plasmas chauds confinés par des champs magnétiques, systèmes physiques qui sont étudiés dans le cadre des recherches sur la fusion thermonucléaire contrôlée. Ces phénomènes de transport sont essentiellement liés à la turbulence électromagnétique et ils sont donc extrêmement difficiles à modéliser par la théorie. Des expériences spécifiques sont alors réalisées sur des machines expérimentales, telles que les tokamaks ou les stellarators, afin d'améliorer la connaissance de ces phénomènes. Cette thèse décrit des études expérimentales de ce type réalisées sur deux tokamaks de grande dimension: Tore Supra (machine basée au CEA/Cadarache) et HL-2A (basée au South-Western Institute of Physics, Chengdu, Chine). La technique utilisée consiste à injecter, de façon modulée dans le temps, des ondes de forte puissance afin de perturber la température électronique du plasma, et des faisceaux supersoniques de particules pour en perturber la densité. La température est mesurée par l'Emission Cyclotronique Electronique et la densité par Réflectométrie micro-onde. Ces expériences on mis en évidence une convection de la chaleur vers l'intérieur du plasma (un phénomène dont l'existence est toujours controversée), et des effets dus aux termes non-diagonaux de la matrice de transport. Ces résultats ont été comparés aux modèles de transport existants.Heat and particle transport is one of the fundamental subjects of research in the physics of hot plasmas confined by magnetic fields, a class of physical systems that are studied in the framework of research on controlled thermonuclear fusion. These transport phenomena are mainly related to electromagnetic turbulence and are therefore extremely difficult to model at a first-principle level. Specific experiments in this area, on plasma devices such as tokamaks or stellarators, are widely used to improve understanding of these phenomena. This thesis reports on experimental studies performed on two large tokamaks : Tore Supra (based at CEA/Cadarache, France) and HL-2A (based at the South-Western Institute of Physics, Chengdu, China). The technique used consists in modulated injection of wave power to perturb the electron temperature and/or of Supersonic Molecular Beams to perturb the plasma density. Temperature is then measured by Electron Cyclotron Emission and density by Reflectometry, and Fourier analysis is used to determine the transport properties. Evidence has been found of inward heat convection (a phenomenon whose existence is still controversial) as well as of peculiar effects due to the non-diagonal terms of the transport matrix. Comparison with transport models has been carried out

Oscillation Analysis Algorithm for Nonlinear Second-Order Neutral Differential Equations

Differential equations are useful mathematical tools for solving complex problems. Differential equations include ordinary and partial differential equations. Nonlinear equations can express the nonlinear relationship between dependent and independent variables. The nonlinear second-order neutral differential equations studied in this paper are a class of quadratic differentiable equations that include delay terms. According to the t-value interval in the differential equation function, a basis is needed for selecting the initial values of the differential equations. The initial value of the differential equation is calculated with the initial value calculation formula, and the existence of the solution of the nonlinear second-order neutral differential equation is determined using the condensation mapping fixed-point theorem. Thus, the oscillation analysis of nonlinear differential equations is realized. The experimental results indicate that the nonlinear neutral differential equation can analyze the oscillation behavior of the circuit in the Colpitts oscillator by constructing a solution equation for the oscillation frequency and optimizing the circuit design. It provides a more accurate control for practical applications

Designated-Tailoring on {100} Facets of Cu2O Nanostructures: From Octahedral to Its Different Truncated Forms

A facile template-free controlled synthesis of Cu2O architectures from octahedral to its different truncated forms is successfully achieved. It is found that the precursor formation temperature is crucial to the designated-tailoring on the {100} facets of Cu2O crystals, which can modify the ratio (R) between the growth rates along the 〈100〉 and 〈111〉 directions, leading to the formation of the initial structures with different shapes. The multiple morphologies can be evolved from these varied initial structures via the synergic effect of oriented attachment and ripening mechanism. This template-free complex precursor-based solution route has provided an innovative approach to design the {100} facets with different sizes to further enrich the current morphologies of Cu2O crystals

Using CNN with Multi-Level Information Fusion for Image Denoising

Deep convolutional neural networks (CNN) with hierarchical architectures have obtained good results for image denoising. However, in some cases where the noise level is unknown and the image background is complex, it is challenging to obtain robust information through CNN. In this paper, we present a multi-level information fusion CNN (MLIFCNN) in image denoising containing a fine information extraction block (FIEB), a multi-level information interaction block (MIIB), a coarse information refinement block (CIRB), and a reconstruction block (RB). In order to adapt to more complex image backgrounds, FIEB uses parallel group convolution to extract wide-channel information. To enhance the robustness of the obtained information, a MIIB uses residual operations to act in two sub-networks for implementing the interaction of wide and deep information to adapt to the distribution of different noise levels. To enhance the stability of the training denoiser, CIRB stacks common and group convolutions to refine the obtained information. Finally, RB uses a residual operation to act in a single convolution in order to obtain the resultant clean image. Experimental results show that our method is better than many other excellent methods, both in terms of quantitative and qualitative aspects