Beam-excited Plasma Research Articles

Artificial Aurora Experiments and Application to Natural Aurora

A review is given of the effects observed during injections of powerful electron beams from sounding rockets into the upper atmosphere. Data come from in situ particle and wave measurements near a beam emitting rocket and ground-based optical, wideband radiowave, and radar observations. The overall data cannot be explained solely by collisional degradation of energetic electrons but require collisionless beam plasma interactions (BPI) be taken into account. The beam-plasma discharge theory describes the features of the region near a beam-emitting rocket, where the beam-excited plasma waves energize plasma electrons, which then ignite the discharge. The observations far beneath the rocket reveal a double-peak structure of artificial auroral rays, which can be understood in terms of the beam-excited strong Langmuir turbulence being affected by collisions of ionospheric electrons. This leads to the enhanced energization of ionospheric electrons in a narrow layer termed the plasma turbulence layer (PTL), which explains the upper peak. Similar double-peak structures or a sharp upper boundary in rayed auroral arcs have been observed in the auroral ionosphere by optical, radar, and rocket observations, and called Enhanced Aurora. A striking resemblance between Enhanced and Artificial Aurora altitude profiles indicates that they are created by the above BPI process which results in the PTL.

Regimes of enhanced electromagnetic emission in beam-plasma interactions

The ways to improve the efficiency of electromagnetic waves generation in laboratory experiments with high-current relativistic electron beams injected into a magnetized plasma are discussed. It is known that such a beam can lose, in a plasma, a significant part of its energy by exciting a high level of turbulence and heating plasma electrons. Beam-excited plasma oscillations may simultaneously participate in nonlinear processes resulting in a fundamental and second harmonic emissions. It is obvious, however, that in the developed plasma turbulence the role of these emissions in the total energy balance is always negligible. In this paper, we investigate whether electromagnetic radiation generated in the beam-plasma system can be sufficiently enhanced by the direct linear conversion of resonant beam-driven modes into electromagnetic ones on preformed regular inhomogeneities of plasma density. Due to the high power of relativistic electron beams, the mechanism discussed may become the basis for the generator of powerful sub-terahertz radiation.

Two-dimensional simulations of nonlinear beam-plasma interaction in isotropic and magnetized plasmas

Nonlinear interaction of a low density electron beam with an uniform plasma is studied using two-dimensional particle-in-cell simulations. We focus on formation of coherent phase space structures in the case, when a wide two-dimensional wave spectrum is driven unstable, and we also study how nonlinear evolution of these structures is affected by the external magnetic field. In the case of isotropic plasma, nonlinear buildup of filamentation modes due to the combined effects of two-stream and oblique instabilities is found to exist and growth mechanisms of secondary instabilities destroying the Bernstein-Green-Kruskal–type nonlinear wave are identified. In the weak magnetic field, the energy of beam-excited plasma waves at the nonlinear stage of beam-plasma interaction goes predominantly to the short-wavelength upper-hybrid waves propagating parallel to the magnetic field, whereas in the strong magnetic field, the spectral energy is transferred to the electrostatic whistlers with oblique propagation.

Whistler-Langmuir oscillitons and their relation to auroral hiss

Abstract. A new type of oscilliton (soliton with superimposed spatial oscillations) is described which arises in plasmas if the electron cyclotron frequency Ωe is larger than the electron plasma frequency ωe, which is a typical situation for auroral regions in planetary magnetospheres. Both high-frequency modes of concern, the Langmuir and the whistler wave, are completely decoupled if they propagate parallel to the magnetic field. However, for oblique propagation two mixed modes are created with longitudinal and transverse electric field components. The lower mode (in the literature commonly called the whistler mode, e.g. Gurnett et al., 1983) has whistler wave characteristics at small wave numbers and asymptotically transforms into the Langmuir mode. As a consequence of the coupling between these two modes, with different phase velocity dependence, a maximum in phase velocity appears at finite wave number. The occurrence of such a particular point where phase and group velocity coincide creates the condition for the existence of a new type of oscillating nonlinear stationary structure, which we call the whistler-Langmuir (WL) oscilliton. After determining, by means of stationary dispersion theory, the parameter regime in which WL oscillitons exist, their spatial profiles are calculated within the framework of cold (non-relativistic) fluid theory. Particle-in-cell (PIC) simulations are used to demonstrate the formation of WL oscillitons which seem to play an important role in understanding electron beam-excited plasma radiation that is observed as auroral hiss in planetary magnetospheres far away from the source region.

Low-temperature nitriding of titanium in low-energy electron beam excited plasma

The effect of an electron beam and the related plasma on the structure, phase state, and microhardness of the surface of titanium has been studied in a broad range of beam currents (0.1–2.5 A), electron energies (0.1–1 keV), and gas pressures (0.01–1 Pa). This range was ensured by the grid stabilization of emissive properties of the plasma electron source, which formed a wide (∼40 cm2) electron beam in a space charge layer between the beam-excited plasma and the grid bounding the plasma cathode. The sample temperature (350–900°C) was determined by the electron beam parameters. The plasma density was additionally controlled by changing the gas (N2 or Ar-N2 mixture) pressure. It is established that, during the low-temperature nitriding process in low-energy electron beam plasma, the ion sputtering significantly affects the microhardness of a processed surface and the rate of growth of the hardened layer thickness. The possibility of nitriding at a low (−50 V) or floating potential of the sample eliminates the development of a surface relief and allows the process to be carried out in deep and narrow slits.

Applications of TiO 2 film for environmental purification deposited by controlled electron beam-excited plasma

Taking advantage of the remarkable features of controlled electron beam-excited plasma (EBEP), the composition and the thickness of TiO 2 film could be directly controlled by the EBEP accelerating voltage V A and discharge current I D, respectively. Experiments were conducted on the dissolving effect on NO x (NO, NO 2) gas using glass beads coated with a TiO 2 film deposited by EBEP. With a bead sample size of 20 g and an NO gas flow rate of 100 ml/min, the NO dissolvable amount was approximately 10 −4 mol/m 2 for 120 min. Using a glass plate, glass beads and zeolites coated with TiO 2 film, the experiments succeeded in dissolving water-soluble ink and in obtaining a hydrophilic effect.

Nonlinear theory of resonant beam-plasma interaction: Nonrelativistic case

Analytic and numerical methods are used to study the nonlinear dynamics of the resonant interaction between a dense nonrelativistic electron beam and a plasma in a spatially bounded system. Regimes such as collective (Raman) and single-particle (Thomson) Cherenkov effects are considered. It is shown that in the first case, the motion of both the beam and plasma electrons exhibits significant nonlinearities. However, because of the weak coupling between the beam and the plasma, the nonlinear dynamics of the instability can be studied analytically and it can be strictly shown that saturation of instability is caused by a nonlinear shift of the radiation frequency and loss of resonance. In the second case, the nonlinear instability dynamics can only be studied numerically. In this regime, at low beam densities significant nonlinearity is only observed in the motion of the beam electrons while the plasma remains linear and saturation of the instability is caused by trapping of beam electrons in the field of the beam-excited plasma wave.

多孔式電子ビーム励起プラズマソースの開発とダイヤモンド様炭素膜の作製

多孔式電子ビーム励起プラズマソースの開発とダイヤモンド様炭素膜の作製

Hot Electron Formation by Beam-Excited Plasma Oscillations

Hot Electron Formation by Beam-Excited Plasma Oscillations