Formation and Diagnostics of Intense Relativistic Helical Electron Beams for Gyrotrons

We develop a magnetron-injection gun for a 1-cm wavelength gyrotron, which allows us to increase the operating current up to 50% of the Langmuir current of the gun by reducing the time required to bring electrons to the high-potential region. To measure the velocity distributions in helical electron beams for energies of several hundreds of keV, we propose, develop, and study a new electron-velocity distribution analyzer based on the phenomenon of electron reflection from an adiabatic magnetic mirror. The results of our study demonstrate that the gun is capable of forming high-quality intense beams suitable for generating microsecond microwave radiation with power higher than 10 MW in gyrotrons.     

Surface Wave Generation in a Solid State Plasma by Relativistic Electron Beams

The linear and nonlinear theory of the surface wave generation in solid-state plasma by a relativistic electron beam propagating in a gaseous plasma is treated. The proposed scheme is in better agreement with the conditions of real experiment. Besides, the neutralization of beam charge is possible and the oscillation frequency and its stability increase, etc. A nonlinear analysis permits to obtain the estimation of efficiency of the beam interaction with the surface wave and a number of other characteristics of the system.     

Numerical Simulation Models of Forming Systems of Intense Gyrotron Helical Electron Beams

Potentialities of different numerical models for calculation of helical electron beams parameters are analyzed. The most simple and economical with respect to the calculation time static mono-velocity model, as well as the model considering initial velocities of electrons and the dynamic model based on the PIC-method and on the quasi-static concept of the electric field are described. The main physical results obtained on the basis if each model mentioned above are given.     

空间电荷阻抗和纵向束团定态解

回顾了加速器的阻抗模型,讨论了空间电荷阻抗和管道壁阻的高频衰减特性.从Vlasov?Maxwell方程出发提出了当存在类似空间电荷阻抗时,在任意外场、任意分布下,束团定态分布的一般解法,并以两种重要分布为例,给出重离子加速器强流参数下的定态分布.解得的定态分布可以进一步应用于稳定性分析和计算机模拟计算.由定态分布的求解得出了对束团中的朗道阻尼和稳定性研究非常重要的纵向“色散”函数.     

Injection of Intense Relativistic Electron Beams into a Toroidal Geometry

Two experimentally verified methods are presented for the injection of high-current relativistic electron beams (30 kA, 400 kV) into strong toroidal magnetic fields (1-8 kGauss). Injection is accomplished by contouring the current flow in the stalk of a field-emission cathode to perturb the flux lines only during beam generation. On conclusion of the emission process the perturbed lines can return to their original positions thereby trapping the beam.     

Linear Theory of Radially Inhomogeneous, Unneutralized, Relativistic Electron Beams

A set of four, coupled, first-order differential equations describing the normal modes of a cylindrically symmetric, cold fluid, unneutralized, relativistic electron beam of arbitrary radial profile is derived. Effects of beam rotation and equilibrium fields are treated exactly. The differential equations are found to have singular points for a radially inhomogeneous beam wherever the eigenfrequency equals the cyclotron or Doppler resonance frequencies. The resulting branch cuts in the dispersion function give rise to secularly decaying contributions to the initial value problem. The rate of decay and the character of the eigenmode near the singularity are determined from the solution of the corresponding indicial equation. Discrete eigenmodes also exist and are obtained by numerical solution of the differential equations and boundary conditions. For realistic solid-beam equilibria, only one slow cyclotron-mode exists for any given pair of axial and azimuthal wavenumbers, and that mode is localized at the beam edge. Under identical conditions several slow space-charge modes exist and are not so distorted. However, even at the space-charge limit, the phase velocity of long-wavelength slow space-charge waves does not decrease to zero. These results are relevant to the Autoresonant and Converging Guide collective ion acceleration proposals.     

Threshold Frequency of Helical Electron–Hole Plasma Instability

Experimental evidence on the dependence of the threshold frequency of silicon oscillistors on the threshold electric field strength, magnetic induction, temperature, and injecting-contact separation is presented. In the temperature interval, where the weak magnetic field criterion is roughly satisfied, the experimental results are shown to be adequately explained by the classical theory of the bulk helical instability of an extrinsic plasma. The threshold frequency in this temperature interval is determined by the sum of two components. One component is due to the ambipolar drift of helical plasma perturbations, and the other results from the presence of the charge-carrier concentration gradient in a direction normal to the vectors of the electric field strength and magnetic induction. In short oscillistors (0.85·10^–3, 2.38·10^–3 m) at 77 K, a semiconductor plasma, wherein the helical instability is excited, approximates an intrinsic plasma, and the threshold frequency is determined by the rotation rate of helical perturbations.     

Condition for Injection of Intense Relativistic Electron Beams into a Z Pinch

Intense relativistic electron beams have been injected into the plasma of a Z pinch at various times during the formation of the plasma column. If the diameter of the plasma column exceeded a certain value, these beams were found to propagate with a high transport efficiency when injected either into the collapsing current sheet of the Z pinch or into the expanding plasma column after its diameter had reached a minimum. However, when the diameter of the plasma column is smaller than this critical value, the relativistic electron beam does not propagate. Instead, it continues to diverge until it strikes the glass wall of the Z pinch tube.     

Low Frequency Rf Heating with a Helical Coupler in a Hot Electron Plasma

A magnetic mirror (mirror ratio 2.38:1) containing ECRH generated hydrogen plasma, with a density of 5 x 1010 cm-3 with cold electron temperature of 11 eV, was used to study propagation of an artificially launched wave varying as ej(?t + m? - kz) at approximately the ion cyclotron frequency. The wave was transmitted between two similar internally placed helically wound antennas separated by 11 wavelengths. The coupling between them was enhanced by as much as 50 times in the presence of plasma. The m = 1 left-handed component was cut off when ? > ?ci. Electron temperatures could be increased by more than 2 times with the m = 1 mode, presumably due to ion heating. Little pump-out was observed.     

On the Application of Pulsed Beams with a Wide Electron Kinetic Energy Spectrum

Russian Physics Journal - The application features of pulsed electron beams with a wide electron kinetic energy spectrum for solving practical problems are considered on the example of wheat seed...     

共振、混沌与束晕形成

研究强流束中的非线性共振、混沌与束晕形成的关系.给出强流束中非线性共振范围的表达式及其随束流空间电荷效应变化的数值结果和图表曲线,提出由非线性共振而激发的束晕形成的空间电荷效应极限,并分析束晕形成的过程.     

Coherence Volume of an Optical Wave Field with Broad Frequency and Angular Spectra

We consider the sizes of a region in a three-dimensional space in which an optical wave field excites mutually coherent perturbations. We discuss the conditions under which the length of this region along the direction of propagation of the wave field and, correspondingly, its volume are determined either by the width of the frequency spectrum of the field or by the width of its angular spectrum, or by the parameters of these spectra simultaneously. We obtain expressions for estimating extremely small values of the coherence volume of the fields with a broad frequency spectrum and an extremely broad angular spectrum. Using the notion of instantaneous speckle-modulation of the wave field, we give a physical interpretation to the occurrence of a limited coherence volume of the field. The length of the spatiotemporal coherence region in which mutually coherent perturbations occur at different times is determined. The coherence volume of a wave field that illuminates an object in high-resolution microscopy with frequency broadband light is considered. The conditions for the dominant influence of the angular or frequency spectra on the longitudinal length of the coherence region are given, and the conditions for the influence of the frequency spectrum width on the transverse coherence of the wave field are examined. We show that, when using fields with broad and ultrabroad spectra in high-resolution microscopy, this influence should be taken into account.     

Gyrotron Backward Wave Oscillator Experiments with a Relativistic Electron Beam Using an X-Band Rectangular Waveguide

A mildly relativistic electron beam (500keV, 200A, 10ns) injected into an X-band rectangular waveguide immersed in a uniform axial magnetic field (4-10kG) produced magnetically tunable microwave radiation in the 9-13 GHz frequency range with an estimated output power of 1MW. The frequency range and tunability of the radiated microwave agreed with a theoretical model for a gyrotron backward wave oscillator taking into account the low energy component of the beam electron.     

Self-Injection and Acceleration of Monoenergetic Electron Beams from Laser Wakefield Accelerators in a Highly Relativistic Regime

Self-injection and acceleration of monoenergetic electron beams from laser wakefield accelerators are first investigated in the highly relativistic regime, using 100 TW class, 27 fs laser pulses. Quasi-monoenergetic multi- bunched beams with energies as high as multi-hundredMeV are observed with simultaneous measurements of side-scattering emissions that indicate the formation of self-channelfing and self-injection of electrons into a plasma wake, referred to as a ＇bubble＇. The three-dimensional particle-in-cell simulations confirmed multiple self-injection of electron bunches into the bubble and their beam acceleration with gradient of 1.5 GeV/cm.     

Computed Tidal Relativistic Red-Shifts of Frequency Standards on Earth and in Space Stations

Frequencies of frequency standards are shifted by the local static gravity red shifts and also modulated by the tidal relativistic red shifts. We compute the tidal relativistic red shifts using a time-domain method and present the numerical results for the National Institute of Metrology(NIM) in Beijing, Laboratoire National de Metrologie et Essais-Systeme de References Temps-Espace(LNE-SYRTE) in Paris and Physikalisch-Technische Bundesanstalt(PTB) in Braunschweig. The differences of the tidal relativistic red shift approach as large as 1.1×10~(-16) when frequency standards at NIM are compared with those at SYRTE and PTB. Moreover, the tidal relativistic red shifts of frequency standards in space stations are also computed.     

Instantaneous Speckle Structures in a Partially Coherent Optical Wave Field with Broad Frequency and Angular Spectra

Optics and Spectroscopy - We consider the hypothesis of instantaneous volume speckle structures in a partially coherent optical wave field of frequency-broadband radiation from an extended light...     

Two-Stream Free Electron Lasers: Physical Analysis of the Systems with Monochromatic Pumping

Nonlinear selfconsistent theory of the Two-stream Superheterodyne Free Electron Lasers (TSFELs) is represented. The one-sectional and klystron type models of TSFEL-amplifiers are analyzed. It is shown that such systems can provide extremely high levels of amplification, and, at the same time, high levels of the input-output decoupling.     

Frequency Spectrum of Plasma-Filled Free-Electron Laser Pumped by Electromagnetic Wave

The frequency spectrum of free-electron laser pumped by electromagnetic wave with magnetized and unmagnetized background plasma is analyzed by the theory of three-wave interaction and PIC simulation, respectively. The frequencies of PIC simulation are in agreement with the results of the three-wave interaction theory. The results show that the frequency spectrum is very plentiful.