Fundamental Plasma Physics最新文献

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.

A recent proposal of accelerator based fusion reactor considers a scheme where an ion beam from the accelerator hits the target plasma on the resonance of the fusion reaction so that the reactivity (σv) can be an order of magnitude larger than that of a thermonuclear reactor. One of the important inputs is the stopping power which is needed to assess the energy loss of the beam in the plasma. In this work, we shall use the analytic formulation of Brown, Preston and Singleton [1] to calculate the temperature dependence of the stopping power due to the target $t,{}^{3}H_e$, and ${}^{11}B$ plasmas in the resonance regions of their respective fusion reactions, i.e., $d+t\to n+\alpha ,d+{}^3{H}_e\to p+\alpha$, and $p+{}^{11}B\to 3\alpha$. It is found that the calculated stopping power, especially when the quantum corrections are included, does not go down with temperature as fast at $T^{-3/2}$. Instead it decreases slower, more like $T^{-x}$ with $x\le 1$ in the range of T from ∼ 5 to 50 keV for d on t and ${}^{3}H_e$ plasmas around their resonance energies.

The paper collects and discusses the results obtained in the theoretical investigation of cold plasmas by using a state-to-state self-consistent kinetic approach, coupling chemistry and free electron kinetics. Examples are selected, not only to review the most recent advancements made in updating and extending the chemical model, but also to highlight the role played in all these systems by excited states, either vibrational or electronic, in affecting the plasma evolution in the discharge and in the post-discharge phases in different discharge configurations. The response of the kinetic simulation to the accuracy of the dynamical data describing the collisional processes, to the theoretical scheme adopted for the vibrational levels of molecules, and to the inclusion of the relevant dissociation channels, is discussed also in the light of the comparison with experiments for model validation.

Nonlinear effects in the propagation of perturbations in a dusty electron-ion plasma are studied, considering fully relativistic wave motion. A multifluid model is considered for the particles, from which a KdV equation can be derived. In general, two different soliton solutions are found depending on the kind of dispersion of the KdV equation. We study when the dispersion coefficient of this equation is positive. In this case, two kinds of behavior are possible, one associated with a slow wave mode, another with a fast wave mode. It is shown that, depending on the value of the system parameters, compressive and/or rarefactive solitons, or no soliton at all, can be found and that relativistic effects for ions are much more relevant than for electrons. It is also found that relativistic effects can strongly decrease the soliton amplitude for the slow mode, whereas for the fast mode they can lead to compressive-rarefactive soliton transitions and vice versa, depending on the dust charge density in both modes.

Radiative cooling of electron beams interacting with counter-propagating electromagnetic waves is analyzed, taking into account the quantum modification of the radiation friction force. Central attention is paid to the evolution of the energy spectrum of electrons accelerated by the laser wake field acceleration mechanism. As an electron beam loses energy to radiation, the mean energy decreases and the form of the energy distribution also changes due to quantum-mechanical spectral broadening.

Machine learning methods have been widely used in the investigations of the complex plasmas. In this paper, we demonstrate that the unsupervised convolutional neural network can be applied to obtain the melting line in the two-dimensional complex plasmas based on the Langevin dynamics simulation results. The training samples do not need to be labeled. The resulting melting line coincides with those obtained by the analysis of hexatic order parameter and supervised machine learning method.

In magnetically confined plasma, it is possible to qualitatively describe the magnetic field configuration via phase spaces of suitable symplectic maps. These phase spaces are of mixed type, where chaos coexists with regular motion, and the complete understanding of the complex dynamical evolution of chaotic trajectories is a challenge that, when overcome, may provide further knowledge into the behaviour of confined fusion plasma. This work presents two numerical investigations into characteristics of mixed phase spaces which model distinct magnetic configurations in tokamaks under different perturbation regimes. The first approach relies on a recurrence-based analysis of ensembles of chaotic trajectories to detect open field lines that widely differ from the average. The second focuses on the transient dynamical behaviour of field lines before they escape the systems. These two methods provide insights into the influence of stickiness and invariant manifolds on the evolution of chaotic trajectories, improving our understanding of how these features affect transport and diffusion properties in mixed phase spaces. These theoretical and numerical approaches may enhance our comprehension of confined plasma behaviour and plasma-wall interactions.

This paper explores the transition between Compton Scattering and Inverse Compton Scattering (ICS), which is characterized by an equal exchange of energy and momentum between the colliding particles (electrons and photons). This regime has been called Symmetric Compton Scattering (SCS) and has the unique property of eliminating the energy-angle correlation of scattered photons, and, when the electron recoil is large, transferring monochromaticity from one colliding beam to the other, resulting in back-scattered photon beams that are intrinsically monochromatic. The paper suggests that large-recoil SCS or quasi-SCS can be used to design compact intrinsic monochromatic γ-ray sources based on compact linacs, thus avoiding the use of GeV-class electron beams together with powerful laser/optical systems as those typically required for ICS sources. Furthermore, at low recoil and low energy collisions (in the 10 keV energy range), SCS can be exploited to heat the colliding electron beam, which is widely scattered with large transverse momenta over the entire solid angle, offering a technique to trap electrons into magnetic bottles for plasma heating.

Since a fusion reactor using the Deuterium-Tritium fuel cycle cannot be a source of clean energy because of the deleterious effects of energetic neutrons carrying 80% of the energy output, and it is very doubtful that it will be able to achieve Tritium self-sufficiency because of an extremely problematic and still unproven breeding procedure, this paper proposes a new reactor scheme capable of confining hot and dense plasmas using the Deuterium – Helium-3 fuel cycle. Such a reactor must be considered a source of clean energy because of its very low level of neutrons production, and its fuel is available in large quantity since we can get the needed Deuterium from seawater and likewise Helium-3 from the moon, as it was found from the samples of lunar soil brought back by the astronauts of the Apollo Mission. The proposed reactor consists of two 100 m long cylindrical plasmas, connected by semicircular sections to form a racetrack configuration. It should be capable of producing from 16 to 20 GW of fusion power when operating with an electron density of 3 × 10²⁰ m⁻³, a magnetic field of 10 T and average temperatures from 40 to 45 keV. Out of this power, up to 10 GW will be used for replacing the loss of electron energy from bremsstrahlung radiation, with a consequent reduction in the reactor power output. However, such a loss could be mitigated by a partial recovery of the energy plasma radiation.

Magnetic reconnection (MR) is a fundamental process in space and laboratory plasmas. The appearance of high power lasers opens a new way to investigate MR under the relativistic condition. In this paper, relativistic collisionless MR driven by two ultra-intense lasers and a pair of asymmetric targets is studied numerically via the kinetic simulations. The static magnetic fields produced by the electron vortex structures with opposite magnetic polarities approach each other driven by the magnetic pressure and the density gradient. The antiparallel magnetic fields annihilate accompanied with the topological variation and the corresponding magnetic field energy is being dissipated to the kinetic energy of the nonthermal charged particles. Besides the outflows along the current sheet, a fast particle bunch is accelerated perpendicularly contributed by the displacement current.