Fundamental Plasma Physics最新文献

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.

In tokamak-confined plasmas, particle transport can be reduced by modifying the radial electric field. In this paper, we investigate the influence of both a well-like and a hill-like shaped radial electric field profile on the creation of shearless transport barriers (STBs) at the plasma edge, which are a type of barrier that can prevent chaotic transport and are related to the presence of extreme values in the rotation number profile. For that, we apply an $E\times B$ drift model to describe test particle orbits in large aspect-ratio tokamaks. We show how these barriers depend on the electrostatic fluctuation amplitudes and on the width and depth (height) of the radial electric field well-like (hill-like) profile. We find that, as the depth (height) increases, the STB at the plasma edge becomes more resistant to fluctuations, enabling access to an improved confinement regime that prevents chaotic transport. We also present parameter spaces with the radial electric field parameters, indicating the STB existence for several electric field configurations at the plasma edge, for which we obtain a fractal structure at the barrier/non-barrier frontier, typical of quasi-integrable Hamiltonian systems.

Elongated tokamak plasmas are prone to instability, initiated by vertical displacement perturbations, which can be suppressed if a perfectly conductive wall is placed near the plasma boundary, providing passive feedback stabilization. For the more realistic case of a resistive wall, the vertical mode can still grow on the relatively slow resistive wall time scale. Active feedback control is then required for complete stabilization. However, the slow growth is far from ideal-MHD marginal stability on the stable side, i.e., provided that the wall is sufficiently close to the plasma. It is shown that the resistive growth rate can be significantly faster, scaling with fractional powers of wall resistivity, if the wall position satisfies the criterion for ideal-MHD marginal stability, thus posing more stringent conditions for active feedback stabilization.

Three geometric formulations of the Hamiltonian structure of the macroscopic Maxwell equations are given: one in terms of the double de Rham complex, one in terms of $L^2$ duality, and one utilizing an abstract notion of duality. The final of these is used to express the geometric and Hamiltonian structure of kinetic theories in general media. The Poisson bracket so stated is explicitly metric free. Finally, as a special case, the Lorentz covariance of such kinetic theories is investigated. We obtain a Lorentz covariant kinetic theory coupled to nonlinear electrodynamics such as Born-Infeld or Euler-Heisenberg electrodynamics.

Helical plasma structures have been identified and shown to form in and propagate from the high density plasmas in which Black Hole binaries can be imbedded. These structures are envisioned to extend to very low density and distant plasma regions up to where they can be disrupted by encountering plasma patches where the waves, of which the structures are composed, become dissipated. By now experimental observations and analyses of the morphology of jets have found that they can involve double-helix magnetic topologies in one case and, more recently, a single helix in other cases. Thus, plasma structures originating in the plasmas surrounding binary systems are proposed, instead of particle beams emitted by black holes directly, as a possible explanation of the origin of the highly collimated jets associated with a variety of celestial objects that are currently observed. Theoretically, double-helix structures are found to emerge as non-linearly coupled torsional ion-sound waves which, in the presence of a background magnetic field, in both the formation and terminal plasmas generate helical magnetic field configurations while remaining nearly “electrostatic” in regions where no significant background magnetic field is present. These (helical) structures can propagate independently in either of the two vertical directions. The coupling involves Intrinsic Gravitational Modes originating in the circumbinary disk and Inner Gravitational Fluctuations emerging from the Swept (Toroidal) Regions carved, within the highest density plasma region, by one or both Black Holes.

Astrophysical jets are plasma flows, which are observed to substantially maintain their transverse size while travelling distances orders-of-magnitude larger. They are found in many astrophysical contexts, spanning several decades in energy and size, suggesting operation of an underlying scale-invariant mechanism. Similar phenomena observed in laboratory plasmas are often studied as surrogate models for astrophysical jets under the conjecture that the scale-invariance of that as-yet-unconfirmed mechanism continues to hold down to laboratory spatial and energy scales. The plasma focus is one such laboratory plasma device which offers the advantage of diagnostic accessibility at a relatively modest resource cost. The present paper uses the plasma focus to address one of the intriguing aspects of the astrophysical jet phenomenon. Theoretical models of astrophysical jets require presence of a poloidal magnetic flux but there is no observational basis for assuming its existence. Indeed, there is a fundamental theoretical impossibility of existence of poloidal magnetic flux in the natural symmetry of the jet phenomena about its axis in the context of magnetohydrodynamics. The next best evidence in support of the poloidal magnetic flux hypothesis of such theoretical models would be to look for it in surrogate experimental simulations of astrophysical jets. In this context, this paper demonstrates a new diagnostic method for detection of poloidal magnetic flux emission from a plasma focus. The results indicate that poloidal magnetic flux continues to be emitted even after the disruption of the plasma focus pinch phase and shows evidence of its being decoupled from the externally supplied discharge current. This observation is interpreted along with previous knowledgebase in terms of a conjecture regarding the scale-invariant mechanism that might also be involved in astrophysical jet phenomena.

Electromagnetic perturbations of a magnetized plasma cause induced charges and currents, collectively known as the plasma response. In the frequency domain, this response is a non-local functional of the electric field. The associated integral kernel, known as the conductivity kernel, is well known in wave-number space, assuming the special case of a homogeneous plasma with a given Maxwellian background distribution function. It is used in this form by many full-wave codes. However, it may be more advantageous to solve the wave problem using a finite element model because of its attractive meshing flexibility. In this paper an exact solution for the conductivity kernel is derived in configuration space, to our knowledge for the first time in 3D. It is valid to all orders in Larmor radius, and up to arbitrary cyclotron harmonic. Future finite element models can be easily constructed using this kernel, which is shown in two simple examples. The model includes mode conversion as well, demonstrated by the second example.

We propose a polytropic-like index that depends on the concentration and number of degrees of freedom of a gas of charged particles following a nonextensive distribution. An equation of state of the gas is obtained and a dispersion relation describing Langmuir waves is derived. Comparison of the acquired dispersion relation with a previous one, recently deduced in the realm of the Kappa distribution, provides an adiabatic map of suprathermal onto nonextensive parameters. In the isothermal limit, the map recovers a well-known relation between those quantities. The results presented here may be useful for investigating the physics of coupled and weakly interacting systems in the nonextensive framework.