Propagation of an Electron Beam in Atmosphere at Altitudes from 15 to 100 km: Numerical Experiment

The propagation of a relativistic electron momentum in the atmosphere is investigated. The motion of electrons under the effect of the geomagnetic and electric force fields, scattering, ionization, the formation of secondary electrons, the perturbation of the atmospheric conductivity, and the distribution of electric field are numerically simulated. The previous conclusion by Neubert et al. [1] is substantiated, according to which the inclusion of the vertical geomagnetic field reduces by almost two orders of magnitude the radial collision blurring of the electron beam and increases accordingly the density of energy release and ionization during the injection from an altitude of 60 km downward. The results are given of simulation of the beam injection at an altitude of 60 km downward or horizontally in the presence of a horizontal or vertical geomagnetic field, as well as of the injection from an altitude of 15 km upward along a quasi-stationary thunderstorm electric field of 5 kV/m beyond the clouds, whose magnitude and polarity correspond to the field jumps that are observed in nature. Based on the calculation results, the degree of ionization, conductivity, and the relaxation time of these parameters in the electron beam trace are estimated. The estimates show that, in the vicinity of the beam trace, because of its polarization, there is a possibility of ten- and hundredfold investigation of the electric field, of discharges in the atmosphere, or of the attainment of the runaway threshold for background relativistic electrons. The possibility is discussed of application of a light electron accelerator for the initiation of observable optical atmospheric phenomena such as blue jets, blue starters, and red sprites.     

Radiation reaction effects on electron nonlinear dynamics and ion acceleration in laser-solid interaction

Radiation Reaction (RR) effects in the interaction of an ultra-intense laser pulse with a thin plasma foil are investigated analytically and by two-dimensional (2D3P) Particle-In-Cell (PIC) simulations. It is found that the radiation reaction force leads to a significant electron cooling and to an increased spatial bunching of both electrons and ions. A fully relativistic kinetic equation including RR effects is discussed and it is shown that RR leads to a contraction of the available phase space volume. The results of our PIC simulations are in qualitative agreement with the predictions of the kinetic theory.     

Observations of the Motion of Single Electrons in Liquid Helium

We have developed an apparatus which can be used to monitor the motion of individual electrons in liquid helium. A sound wave is used to explode an electron bubble for a fraction of a microsecond. While the bubble is expanded, it is illuminated by light from a flash lamp. We describe the details of the experiment and show results obtained. In some cases, an electron is seen to follow a snakelike path. Our tentative explanation is that the electron is sliding along a quantized vortex line. If this interpretation is correct, the recorded track of the electron provides an image of the path of the vortex.     

Localization of intense electromagnetic waves in plasmas

We present theoretical and numerical studies of the interaction between relativistically intense laser light and a two-temperature plasma consisting of one relativistically hot and one cold component of electrons. Such plasmas are frequently encountered in intense laser-plasma experiments where collisionless heating via Raman instabilities leads to a high-energetic tail in the electron distribution function. The electromagnetic waves (EMWs) are governed by the Maxwell equations, and the plasma is governed by the relativistic Vlasov and hydrodynamic equations. Owing to the interaction between the laser light and the plasma, we can have trapping of electrons in the intense wakefield of the laser pulse and the formation of relativistic electron holes (REHs) in which laser light is trapped. Such electron holes are characterized by a non-Maxwellian distribution of electrons where we have trapped and free electron populations. We present a model for the interaction between laser light and REHs, and computer simulations that show the stability and dynamics of the coupled electron hole and EMW envelopes.     

High-power terahertz synchrotron sources

Electromagnetic waves, or light, are produced by accelerating electrons according to the formula assigned the name of Sir Joseph Larmor, who was secretary of The Royal Society from 1901 to 1912. For relativistic electrons the emission is enhanced by the fourth power of the increase in mass. Thus for 10 MeV electrons, for which the mass increases by a factor of 21, the enhancement is a factor of 200000. We have generated high-power broadband THz light using relativistic electrons and demonstrated that ca. 100 W can readily be produced in a band from 0.1 to 3 THz with possible extensions to 6 THz. The experiments use a new generation of light source in which bunches of electrons circulate once, but in which their energy is recovered. In such a machine the electron bunches can be very much shorter than those, say, in storage rings or synchrotrons.     

The generation of mono-energetic electron beams from ultrashort pulse laser-plasma interactions

The physics of the interaction of high-intensity laser pulses with underdense plasma depends not only on the interaction intensity but also on the laser pulse length. We show experimentally that as intensities are increased beyond 10(20) W cm(-2) the peak electron acceleration increases beyond that which can be produced from single stage plasma wave acceleration and it is likely that direct laser acceleration mechanisms begin to play an important role. If, alternatively, the pulse length is reduced such that it approaches the plasma period of a relativistic electron plasma wave, high-power interactions at much lower intensity enable the generation of quasi-mono-energetic beams of relativistic electrons.     

Brittle fracture of solids caused by intense electron beams

In the mid 1960s, powerful pulse electron beam accelerators having a voltage of some millions of volts were invented and later used to fracture various materials. Experimental data analysis allowed discovery of a new mode of fracture in several ductile crystals caused by a specific energy supply to the crack tip. The mode differs from well known thermomechanical modes of fracture caused by the “ heat-thermostress-crack ” mechanism. This new mode is called the electron fracture mode (EFM). It is characterized by the following three special features, (i) Initial macrocracks in a specimen do not affect the threshold of fracture; that is, the value of the beam intensity at which the specimen breaks, (ii) The fracture of different materials, which can be very ductile at usual mechanical loads, occurs in a brittle manner; that is, the specimen usually splits by a crack without any residual deformation, (iii) The splitting cracks propagate with supersonic velocities. These data are controversial from the point of view of common fracture mechanics and, hence, they cannot be understood or explained from the traditional position.The purpose of the present study is to create a simple practical model of the EFM. The basic viewpoint can be briefly summarized as follows: during irradiation of a solid by a high intensity electron beam, some solid plasma clots are formed and act as “ blades ” or “ wedges,” cutting the crystalline specimen.In the Introduction, experimental data on the EFM are analyzed and discussed, while the peculiarities of the EFM are specified. As a result, it is concluded that the processes caused by the EFM are unusual for the common concepts of fracture mechanics. In Section 2 the invariant Γ-integrals of an electromagnetic deformable medium are modified for supersonic singularities. The basic model and some problems serving to explain and describe the EFM are formulated. In Section 3, the relativistic electron interactions in beams are considered. Using Γ-integrals, we derive the law of the interaction of two moving relativistic charges; that is, the generalized Coulomb's law for relativistic charges. In particular, when two relativistic electrons, e, move with the same velocity, v, one behind the other along a rectilinear trajectory, the force, F, acting upon the rear electron is equal to: where R is the distance between the electrons, c is the speed of light in the vacuum, and a is the phase-speed of light in a medium having electromagnetic constants, μ, , and '. It appears that two electrons moving faster than the phase-speed of light attract one to the other, as distinct from the common Coulomb law. Hence, the beams of such relativistic electrons tend to self-pack and self-compress. The latter problem is studied using a periodic chain model of the electron beam. In Section 4, the dynamic elastic problem of supersonic cutting by a thin wedge is formulated and solved, and the drag force is calculated. In Section 5, the problem of deceleration of the moving wedge is solved in quasi-steady approximation. The length of a resulting cut, that is, the final crack, is determined. Some applications of the analytical solutions are given. In Section 6, the theoretical results are analyzed and compared with experimental results. The role of relativistic electrons is estimated and some parameters of solid-state electron plasma clots are defined. In the Conclusion, the necessity of further study of this mysterious phenomenon is emphasized.     

Disruption of the stationary state and electrical breakdown in amorphous dielectrics II. Ionic dielectrics

A phenomenological model is proposed for ionic dielectrics which describes the condition for disruption of the stationary state of conduction electrons emitted from localized sites in the high mobility band and accelerated up to the energy of avalanche ionization. It is found that the electric strength of amorphous ionic dielectrics decreases with increase in film thickness and temperature. The influence of the intensity of interaction of delocalized electrons with optical phonons in polar amorphous dielectrics, the character of the interconnection of an electron with a trap and the correlation between the states on electrical breakdown are investigated.     

Coherent bremsstrahlung and parametric X-ray radiation from nonrelativistic electrons in a crystal

X-ray radiation generated by nonrelativistic electrons interacting with a crystal target exhibits several distinctive features in comparison to the relativistic case. The difference is related to the interference of the parametric X-ray radiation and coherent bremsstrahlung, which takes place for the nonrelativistic electrons. The characteristics of this radiation have been studied in the Bragg and Laue geometries in an electron microscope using a beam of electrons with energies in the 50–100 keV range. The necessary requirements on the target parameters, the measuring instrumentation, and the experimental geometry are established. Variation of the X-ray radiation frequency depending on the angle of electron beam incidence on the target in the region of non-relativistic electron energies has been observed for the first time. The X-ray radiation frequency has been also studied as a function of the primary electron beam energy. Tunable soft X-ray radiation with quantum energy in the range below 1 keV is obtained. The radiation quantum yield per electron within a unit solid angle amounts to ～10^?8.     

Classification of the interactions of relativistic electrons with laser radiation

The interactions of relativistic electrons with laser radiation are classified in terms of three Lorentz-invariant quantities, which can be determined using the laser radiation parameters and the electron energy. The proposed classification covers the entire range of electron energies and laser radiation intensities presently in use, with allowance for quantum effects and nonlinear processes of higher harmonic generation.     

A two-channel relativistic backward-wave generator with 8-mm range, controllable phase difference, and channel power of 230 MW

The coherent composition of the wave beams of two relativistic nanosecond backward-wave tubes (BWTs) with an 8-mm range and peak power in each channel of up to 230 MW is implemented. A specific feature of this experiment was power supply of explosive-emission cathodes by split pulses supplied by a completely solid-phase SOS modulator with reduced amplitude scatter. The voltage growth rate was increased compared to previous experiments, which made it possible to transition to the region of weaker magnetic fields ～2 T, which was less than cyclotron resonance field, while retaining stable emission of the electron beams. As a result, a standard deviation of phase scatter between the channels of 0.5 ps was found on the time scale.     

高功率微波源用电子收集极材料:强流高能电子束轰击下的物理效应及对材料性能的要求

高功率微波源用收集极用于接收束波耦合作用后的强流电子束,是影响高功率微波源稳定性和寿命的关键部件。收集极在强流电子束的轰击下会产生二次电子、背散射电子、韧致辐射等物理效应,将引起微波品质的降低。电子束的能量沉积在收集极上会产生显著的温升效应,从而导致收集极效能下降甚至结构失效,同时材料在强流电子束的轰击下会发生蒸发而污染腔室,降低系统绝缘性。在讨论分析强流电子束轰击材料所产生的物理效应机制及其影响因素的基础上,分析了高功率微波源用收集极材料的性能要求。     

Spin precession of electrons reflected from a ferromagnetic surface

The reflection of spin-polarized electrons from polycrystalline ferromagnetic films is investigated in a “complete” scattering experiment, where a spin-polarized electron source is combined with a spin polarization detector. The spin polarization vector of the electrons is shown to precess during reflection about the magnetization direction of the ferromagnetic film. Consequently, a torque is generated on the magnetization by the reflected electrons.     

Basic concepts in plasma accelerators

In this article, we present the underlying physics and the present status of high gradient and high-energy plasma accelerators. With the development of compact short pulse high-brightness lasers and electron and positron beams, new areas of studies for laser/particle beam-matter interactions is opening up. A number of methods are being pursued vigorously to achieve ultra-high-acceleration gradients. These include the plasma beat wave accelerator (PBWA) mechanism which uses conventional long pulse ( approximately 100 ps) modest intensity lasers (I approximately 10(14)-10(16) W cm(-2)), the laser wakefield accelerator (LWFA) which uses the new breed of compact high-brightness lasers (<1 ps) and intensities >10(18) W cm(-2), self-modulated laser wakefield accelerator (SMLWFA) concept which combines elements of stimulated Raman forward scattering (SRFS) and electron acceleration by nonlinear plasma waves excited by relativistic electron and positron bunches the plasma wakefield accelerator.In the ultra-high intensity regime, laser/particle beam-plasma interactions are highly nonlinear and relativistic, leading to new phenomenon such as the plasma wakefield excitation for particle acceleration, relativistic self-focusing and guiding of laser beams, high-harmonic generation, acceleration of electrons, positrons, protons and photons. Fields greater than 1 GV cm(-1) have been generated with monoenergetic particle beams accelerated to about 100 MeV in millimetre distances recorded. Plasma wakefields driven by both electron and positron beams at the Stanford linear accelerator centre (SLAC) facility have accelerated the tail of the beams.     

Effect of self-generated axial magnetic field and on propagation of intense laser radiation in plasmas

The present paper deals with an analytical study of a self-generated axial magnetic field (SGAMF) through the inverse Faraday effect (IFE) and its influence on the propagation of circularly polarized light wave for relativistic intensities. As a first step, the non-linear dielectric constant incorporating a magnetic field in the relativistic factor within the framework of WKB (for Wentzel, Kramers, and Brillouin) and a paraxial ray theory is formulated. It is noticed that for intensities (>10¹⁸ W cm^?2), circularly polarized radiation can propagate in electron plasma whose density is greater than the critical density as well as a strong flow of relativistic electrons, axially co-moving with the pulse rise. The above generates a magnetic field up to 100 MG and strongly influences the light propagation. Two modes of propagation exist, namely, extraordinary and ordinary, and critical power for focusing is different for the two modes. The non-linear dielectric tensor, propagation equation, and the self-trapped radius are evaluated incorporating an induced magnetic field. The focusing conditions strongly depend on the power of the beam, strength of the magnetic field as well as on the density of the medium. Numerical calculations are made for a typical set of relativistic laser plasma interaction processes.     

A quantum stochastic equation describing evolution of the transverse energy of a channeled particle

A stochastic equation describing evolution of the nth quantum energy level of a relativistic electron (positron) moving in planar channels of a crystal is derived using the condition of conservation of the transverse motion energy comprising a sum of the energies of interaction with atomic electrons and crystal lattice nuclei.     

Field emission from carbon nanotubes in DC and pulsed mode

Multi-wall Carbon Nanotube (CNT) emitters were tested in a combined diode-RF electron gun. Field emission of the nanotubes was observed at 5-30 MV/m, using a 250 ns FWHM long pulse with a peak voltage of 80-470 kV. The field emission threshold is compatible with that found from previous DC testing. We have extracted from a continuous field emitter up to a nanoCoulomb of charge and measured an emittance of 4 mm mrad with a 2 pC electron beam. The total charge emission during RF operation, using the 1.5 GHz, 2 cell RF structure, was found dependent on its period. RF operation showed that back bombarding electrons with up to 5 MeV did not impair the emission stability of the CNTs.     

The effect of the conductivity of drift chamber walls on the dynamics of a relativistic electron beam with a virtual cathode

The effect of conductivity of walls of a drift chamber of the axial vircator on the behavior of a relativistic electron beam with a supercritical current was investigated. The dynamics of a relativistic electron beam is shown to be characterized by the formation of a virtual cathode of complex structure with two or three potential minima in the azimuthal direction, which rotate around the drift space axis. It is established that variation in the conductivity of drift chamber walls leads to stepwise switching of the generation frequency and a sharp change in the output power. Dependences of the output radiation power of the investigated vircator system on the conductivity of drift chamber walls for two characteristic regimes of the dynamics of a relativistic electron beam were obtained.     

Giant Rashba-type spin splitting in bulk BiTeI

There has been increasing interest in phenomena emerging from relativistic electrons in a solid, which have a potential impact on spintronics and magnetoelectrics. One example is the Rashba effect, which lifts the electron-spin degeneracy as a consequence of spin-orbit interaction under broken inversion symmetry. A high-energy-scale Rashba spin splitting is highly desirable for enhancing the coupling between electron spins and electricity relevant for spintronic functions. Here we describe the finding of a huge spin-orbit interaction effect in a polar semiconductor composed of heavy elements, BiTeI, where the bulk carriers are ruled by large Rashba-like spin splitting. The band splitting and its spin polarization obtained by spin- and angle-resolved photoemission spectroscopy are well in accord with relativistic first-principles calculations, confirming that the spin splitting is indeed derived from bulk atomic configurations. Together with the feasibility of carrier-doping control, the giant-Rashba semiconductor BiTeI possesses excellent potential for application to various spin-dependent electronic functions.     

The magnicon — An advanced version of the gyrocon

A new VHF generator with circular deflection of a high power relativistic electron beam is described as an outgrowing of the gyrocon proposed by Budker in 1967.The output resonator of the device is placed in a static magnetic field providing synchronous interaction of electrons with the electromagnetic field. An accompanying magnetic field and prolonged time of interaction enable one to achieve higher power within the decimeter and centimeter wave range compared to that of the gyrocon and klystron due to the higher electrical strength of the output resonator, a decreased heat generation and an easier beam guidance. In order to get higher gain and efficiency the magnicon deflection resonator is also placed in a magnetic field (of double magnitude).Test results for a magnicon of 30 cm wave range built at the INP are given. The power obtained is 2.6 MW for a pulse duration of 30 μs with a repetition rate of 1 Hz and an electron efficiency of 85%.