Hot Electron Beam Research Articles

Electron beam excitation of a potential well in a magnetized plasma waveguide

The evolution and properties of a potential well being excited in a magnetized plasma-filled waveguide by a hot electron beam have been investigated. An equation of KdV-type describing the potential well has been obtained. It is shown that a potential shock is formed near the potential well, the front of the well is steeper than the back, the width of the well decreases with increasing amplitude. The well is determined by two modes with a linear dispersion relation: by the mode in a magnetized plasma-loaded waveguide and by the electron-acoustic mode.

Electron-acoustic instability driven by a field-aligned hot electron beam

Using kinetic theory, the electron-acoustic instability is investigated in a three-component plasma consisting of a hot electron beam and stationary cool electrons and ions. In the model considered here both the electrons and ions are magnetized, with the beam drift along the external magnetic field. The dependence of the growth rate on plasma parameters, such as electron-beam density, electron-beam speed, magnetic field strength and propagation angle, is studied. In addition, the effects of anisotropies in the velocity distributions of the hot electron beam and the cool electrons on the instability growth rate are examined.

Hot electron beams for FELs

We consider one of the FEL schemes in which the phase velocity of the electromagnetic wave (or the ponderomotive wave) is constant, but the longitudinal electron velocity is changed due to an external magnetic field. There is also an additional magnetic field which turns the electrons back before the interaction. It is shown that the efficiency of utilizing hot electron beams of large current density may be high enough in such systems with a refractive and an undulator medium.

Electron beam acoustic and magneto-acoustic modes in a magnetized beam-plasma system

The dispersion relation characterizing electrostatic modes in a cold magnetized plasma penetrated by a hot electron beam is solved analytically. In the limit k 2 λ 2 b ⪡1 where k is the wavenumber of the mode and λ b is the Debye length of beam elect rons, two new modes, viz. the electron acoustic and the magneto-acoustic mode, are found to exist. Expressions for the growth rate and threshold beam energy required for the onset of the kinetic instabilities of these modes are obtained.

Ballistic hot-electron transistors

We present an overview of work at the IBM Thomas J. Watson Research Center on the tunneling hot-electron transfer amplifier (THETA) device—including its use as an amplifier and as a tool for investigating ballistic hot-electron transport. In the initial, vertically configured version of the device, a quasi-monoenergetic, variable-energy, hot-electron beam is generated (via tunneling) which traverses a thin GaAs region and is then collected and energy-analyzed. As the hot electrons traverse the device, they are used to probe scattering events, band nonparabolicity, size-quantization effects, and intervalley transfer. A recent, lateral version of the device has been used to demonstrate the existence of ballistic hot-electron transport in the plane of a two-dimensional electron gas, and the associated possibility of achieving high gain.

Beam instability of the Z mode in the solar wind

The growth rate of the z mode is calculated assuming a cold magnetized background plasma and a tenuous population of hot electrons. For a weak, but nonvanishing, magnetic field the growth rate is shown to coincide with that of the electrostatic Langmuir wave, i.e., the result when the influence of the ambient magnetic field is only retained for the energetic electrons. Considering the case of a beam of hot electrons, we numerically evaluate the expression for the growth rate for several cases of solar wind plasma conditions. Solution of the full 3×3 dispersion determinant allows the computation of the growth rate and real frequency shift for arbitrary beam densities and magnetic field strength. The influence of the background magnetic field is discussed, and the apparent polarization of the excited waves is calculated assuming a weak density gradient between source and observer. The effect of the beam density, direction of propagation, and magnetic field on the observable polarization is discussed.

Double base hot electron transistor

We propose a novel device concept of focusing a hot-electron beam for ballistic injection. Such a focused beam may be achieved by passing injected electrons through a doped semiconductor layer with a built-in electric field. This leads to a more narrow and energy-monochromatic beam. When such a beam is used in ballistic devices, the device performance should significantly improve. As an example, we propose a novel Double-Base-Hot-Electron Transistor (DBHET). Some preliminary calculations demonstrate that both electron transit time across the active base and the density of high energy electrons improve in DBHETs compared to conventional Hot-electron Transistors (HETs). We also show that the DBHET has better temperature stability because of its more energetic and monochromatic electron beam injected into the active base.

Computer simulation of whistler mode wave‐particle interactions using a free‐boundary encounter model

Computer simulations of whistler mode wave‐particle interactions have been performed by using a free‐boundary encounter model electromagnetic code. The free boundary is attained by adding a collision dominated damping region near one boundary to remove periodicities usually used in electromagnetic codes. In our model, a wave front encounters a resonant bi‐Maxwellian hot electron beam. Spatial amplitude modulations are observed in our simulations. The dips of the amplitude, however, sometimes decrease to zero levels. The null points of the wave magnetic field and the associated phase reversals of the wave cannot be described by the usual particle trapping theory. A component of the field contains a feature reminiscent of a double sideband (DSB) wave without a carrier. This is interpreted as a beat between an incident wave and a generated wave. This phenomenon occurs if the amplitudes of both the waves are almost equal. The results of these simulations provide a possible explanation for the N events observed by Dowden et al. during a VLF injection experiment.

Tunneling hot electron transfer amplifiers (theta): Amplifiers operating up to the infrared

A family of novel three-terminal devices which relies on the transfer of a quasi-monoenergetic hot electron beam through a thin base is described. The devices are similar in principle to the proposed tunneling amplifier by Mead in the early sixties (“Cold Cathode” or “Metal Base” amplifiers). Results are reviewed and the probable reasons for the poor performances are pointed out. It is predicted that, with a proper choice of parameters, metal-base amplifiers can operate as switches, negative resistance devices and continuous amplifiers in the subpicosecond range. Two subclasses are described: The tunneling emitter (THETA), in the major part of the work, and the nontunneling emitter (BHETA) amplifiers. In the THETA family the metal-oxide-metal-oxide-metal (MOMOM), the MOM-semiconductor (MOMS), and the heterojunctions devices are described. Members of the BHETA family generate quasi-monoenergetic electron beams by injecting electrons by an n + n − or a metal- n − junctions, and include a variety of metals and semiconductor combinations. Very thin films are required in these devices (oxides ∼15 Å, metals ∼100 Å, semiconductors ∼100 Å). The molecular beam epitaxy technique and lattice matching considerations are required for pinhole free semiconductors and metal films with minimum interface states. Sputter-oxidation methods are needed for thin oxide growth. Systems which combine these features with availability of microfabrication make these devices feasible today.

Excitation of lower hybrid waves by electron beams in finite geometry plasmas. Part 1. Body waves

The quasi-static lower hybrid eigenmodes of a plasma column in a cylindrical waveguide are determined, and their linear excitation by a small density electron beam is discussed for the cases of a hot electron beam as well as for a cold electron beam. It is shown that under certain conditions, finite geometry effects introduce important quantitative and qualitative differences with respect to the results obtained in an infinite geometry.

Computer simulation of nonlinear interaction between a monochromatic whistler wave and an electron beam

A computer experiment on the self-consistent nonlinear interaction between a large amplitude whistler mode wave propagating along an external magnetic field and plasma particles is described. The plasma is composed of cold electrons, cold ions, and a hot electron beam with the mean velocity around the resonance velocity of the propagating large amplitude whistler mode wave. In addition to an amplitude oscillation of the whistler mode wave, an interesting evolution of the velocity distribution function of the hot beam electrons is observed. These results are first compared with the theory by Palmadesso and Schmidt and then are explained by a simpler physical picture. The computer code for the present simulation followed nonrelativistic dynamics of 3072 electrons in a self-consistent electromagnetic field. The total energy in the system under consideration was conserved well with a maximum numerical error of 0.3%.

Stimulation of VLF amplification in the magnetosphere

Among the various plasma instabilities that exert influence on the dynamic equilibrium state of the magnetosphere, the cyclotron-resonance interaction appears to be the most accessible to artificial stimulation. The strength of the interaction is sensitive to both the background magnetoplasma parameters and the hot energetic particle distribution. Thus, proper modification of one or more conditions can induce significant wave amplification at the expense of hot plasma energy density. Several methods of hot and cold plasma injection have been investigated with the linear theory to assess their effectiveness as a means of stimulating amplification. Only the interaction of VLF waves (3–30 kHz) with hot electrons (0.1–100 keV) is treated here. The injection of a dense jet of barium that travels upward along the geomagnetic field causes appreciable amplification when the jet is within 30° of the geomagnetic equator. Injection of a geosynchronous lithium cloud stimulates amplification of both VLF and ULF waves, but the magnitude depends critically on the state of geomagnetic activity. Conventional hot electron beams may also amplify narrow frequency bands, but the net wave energy is severely limited by the beam energy. Although the cyclotron-resonance is recognized as a dominant interaction in magnetospheric dynamics, its properties have never been confirmed quantitatively by appropriate spacecraft experiments. Controlled injections would provide important insight into this fundamental process because the induced amplification has a well-defined signature.