Fundamental Plasma Physics最新文献

We show how some different fundamental plasma processes - the ideal kink instability, magnetic reconnection and magnetohydrodynamic oscillations - can be causally linked. This is shown through reviewing a series of models of energy release in twisted magnetic flux ropes in the solar corona, representing confined solar flares. 3D magnetohydrodynamic simulations demonstrate that fragmented current sheets develop during the nonlinear phase of the ideal kink instability, leading to multiple magnetic reconnections and the release of stored magnetic energy. By coupling these simulations with a test particle code, we can predict the development of populations of non-thermal electrons and ions, as observed in solar flares, and produce synthetic observables for comparison with observations. We also show that magnetic oscillations arise in the reconnecting loop, although there is no oscillatory external driver, and these lead to pulsations in the microwave emission similar to observed flare quasi-periodic pulsations. Oscillations and propagating waves also arise from reconnection when two twisted flux ropes merge, which is modelled utilising 2D magnetohydrodynamic simulations.

A comprehensive overview is presented of recent theoretical advancements and observational manifestations of a relatively new type of electrostatic solitary wave (ESW), known as supersoliton or supersolitary wave (SSW). These nonlinear structures are characterized by a distorted pulse-shaped electrostatic potential excitations, deviating from the standard (“sech²”-like) form generally expected from solitonic pulses. In Space plasmas, in particular, e.g. in magnetospheric observations, SSWs may be associated with a characteristic wiggly bipolar electric field waveform. It has been shown that a three-component configuration is essential, as a minimum requirement for SSWs to occur in a plasma.

Various spacecraft missions have recorded evidence of “non-conventional” electrostatic solitary waves (pulses) such as wiggly bipolar pulses, offset bipolar pulses, and monopolar pairs. This review article aims to present the current state of the art in this fascinating new theme, first outlining the basic framework for the modeling of such “exotic” ESWs and then putting forward a correlation between SSW structures with certain non-standard bipolar electric field forms observed in planetary magnetospheres.

Superior lifetime stability for the microplasma device developed by decorating nanodiamonds (nDs) on laser induced graphene (LIG) is reported. Upon overwhelming the difficulty of poor stability in graphene, the nD-LIG displays exceptional lifetime stability of 1770s verified at an applied voltage of 340 V. But, the lifetime stability of LIG is only 718 s at the same applied voltage. Therefore, the nD-LIG with enhanced lifetime stability have pronounced prospective as cathodes in microplasma device applications.

We report on the first implementation of a miniature laser-driven shock tube (LDST) of 5 × 5 mm cross section and 50-mm length for generating and studying strong shock waves (SW) and hypersonic gas flows with M > 10. Operation of the LDST is based on the acceleration of a thin CH-film by ablative plasma pressure produced when the film is irradiated by high-energy UV pulse of the GARPUN KrF laser (100 J & 100-ns). The film serves as a piston that pushes a SW in the gas filling the LDST. An optical system based on a multi-element prism raster provides focusing of KrF laser beam into 7 × 7 mm square spot with 100 J/cm² energy fluence (1 GW/cm² intensity) with inhomogeneity ∼3 % across the LDST aperture. It is expected that the LDST with KrF laser driver can be an effective tool for studying hydrodynamic phenomena, such as hydrodynamic instabilities and transition to a turbulence, hypersonic gas flow around bodies, reflection and cumulation of strong SW.

We show that the wakefield driven by fast electrons inside the nanowire when irradiated with an ultra-short relativistic laser pulse strips atoms to a higher charge state. Using particle-in-cell simulations, we demonstrate that the charge state agrees with the barrier suppression threshold of the wakefield and reaches a higher value via collision. The ionisation of gold nanowires occurs only via collisional-damped wakefield. We found that the collisional ionisation of high-Z nanowires depends on the onset of the z pinch. These results suggest a different ionisation mechanism of the structured target in the subfemtosecond regime.

We consider a visco-resistive magnetohydrodynamic modelling of a steady-state incompressible tokamak plasma with a prescribed toroidal current drive, featuring constant resistivity η and viscosity ν. It is shown that the plasma velocity root-mean-square behaves as $\eta f\left(H\right)$ as long as the inertial term remains negligible, where H stands for the Hartmann number $H\equiv {\left(\eta \nu \right)}^{-1/2}$, and that $f\left(H\right)$ exhibits power-law behaviours in the limits $H\ll 1$ and $H\gg 1$. In the latter limit, we establish that $f\left(H\right)$ scales as $H^{1/4}$, which is consistent with numerical results.

High-order harmonic generation is a nonlinear optical frequency conversion process that occurs during intense ultrafast laser-matter interaction. At the Advanced Laser Light Source laboratory, we use ultrafast laser pulses having diverse wavelengths, spanning visible, near- and mid-infrared ranges, to generate high-order harmonics from laser-ablated plumes in the extreme ultraviolet or soft X-ray region of the electromagnetic spectrum. The Advanced Laser Light Source Laboratory is situated within the Énergie Matériaux Télécommunications Center of the Institut national de la recherche scientifique in Montréal, Quebec, Canada. We focus on generating bright and broadband harmonics by exploiting various types of ultrafast resonances in different species within the laser-ablated plume, and use them for applications in ultrafast spectroscopy, imaging, and AMO science. We are also actively exploring previously unknown physics governing the harmonic generation from different resonances. In this review article, we provide an overview of the recent advancements made in these directions.

A complete understanding of the stability of fluid flows under varying magnetic field profiles is imperative for achieving control of plasma and operating fluids in the blankets of future fusion reactors. In this context, the primary objective of this study is to investigate the influence of varying magnetic profiles on the flow regime of a generic fluid, which is representative of both thermonuclear plasma and conductive fluids within a nuclear fusion reactor. To this aim in this work non-modal stability theory is adopted to perform stability analysis of a magneto-hydrodynamic (MHD) flow in an infinite circular pipe in order to study the effects of the magnetic field on the fluid dynamics of the pipe flow. In particular, the effects on the general stability of two magnetic field profiles are compared with the reference case of a pipe Poiseuille flow without magnetic field. Firstly, the classic modal stability technique is employed to study asymptotical stability. Then, non-modal stability analysis is applied to magneto-hydrodynamic pipe flow to study the system's response for a finite time immediately after a perturbation. Fourier–Chebyshev Petrov–Galerkin spectral method is used to compute the eigenvalues and pseudospectra of the weak formulation associated with the linearised system. Investigations on the dependence of spectra and transient growths on the specific magnetic profiles are conducted for different values of perturbation wave numbers. The obtained results show that in general the magnetic field has an effect of stabilization on the system, which depends on the specific magnetic profile considered. In addition, the non-modal stability analysis reveals that the inclusion of the magnetic field mitigates the effects of perturbations also in the short term, a phenomenon that cannot be seen using only modal stability analysis.

We studied the γ-ray emission from laser interactions with structured targets of Al and Au. Bremsstrahlung and Non-linear Compton Scattering (NCS) emission are considered for the γ-ray emission using the open source 2-D PIC code EPOCH. Different shapes of the target generated additional hot electrons, which helps to enhance the photon energy in individual cases. The enhancement of photon energy is due to the target's shape and the hot electrons. Hot electron generation and their dynamics, like refluxing behavior, are crucial phenomena in thin targets. This study uses four different shapes of Al and Au targets. The relative strength of emissions from both bremsstrahlung and NCS are compared. The shape of the target enhances the γ-ray energy, electron energy, and emitted photon number and improves the electron beam divergence. The effect of each target shape on hot electrons refluxing behavior and the role of the electric and magnetic fields are discussed in detail.

Thermal plasma is one of the upcoming powerful tools used for materials processing. It covers a wide range of technological applications such as synthesis of various refractory ceramic materials, metals and alloys, deposition of coatings, high temperature processing of materials as well as disintegration of waste materials. Representative technologically important material systems viz rare earth hexaboride (e.g. GdB₆) and carbonaceous materials are focus of the present manuscript. Both the material systems have been processed using DC thermal plasma route and characterized thoroughly for structural, morphological, surface properties using XRD, TEM, XPS respectively. Morphology of GdB₆ has been tailored by varying plasma parameters during synthesis. Further, these GdB₆ powder were investigated for electron emission performance using Field Electron Emission and maximum current density of 0.5 mA/cm² was noted for the nanocrystalline GdB₆ sample. Feasibility of thermal plasmas for production of nanocrystalline GdB₆ and processing of a bio-waste to obtain technologically important carbonaceous materials has also been explored.