Electron-wave Interaction Research Articles

Formation of high-power microwave dissipative soliton combs based on reactive electron–wave interaction

We theoretically demonstrate the possibility of implementing high-power repetitively pulsed microwave radiation sources based on an analogy with the formation of optical dissipative soliton combs in microresonators with Kerr nonlinearity pumped by laser radiation. A similar mechanism can arise due to electron–wave interaction in a microwave-pumped high-Q resonator when, with near-zero synchronism, detuning, amplification, and absorption are negligible, and the driving electron beam primarily acts as a medium with reactive nonlinearity. The required physical parameters are estimated for observing Ka-band dissipative soliton combs based on an undulator mechanism of electron–wave interaction in a gyrotron-pumped resonator.

Nonadiabatic effects in the electron-optical system of a relativistic millimeter-wave gyrotron

Gyrotrons based on relativistic electron flows generated by thermionic magnetron injection guns are promising pulsed sources of millimeter and submillimeter radiation with multi-megawatt output power. Obviously, to increase the output power of such devices, it is necessary to provide a high beam current of more than 100 A. At the selected emission density, this forces the use of an emitter with a sufficiently large area. As is well known, wide emitters produce beams with a large velocity spread, which reduces the efficiency of the electron-wave interaction. Therefore, it is necessary to increase the diameter and, accordingly, increase the distance from the cathode to the gyrotron cavity, which leads to an increase in the magnetization reversal coefficient. Thus, the magnetic field in the region of beam formation becomes weak, and the Larmor radius and the turn pitch of the electron trajectory become large compared to the geometry of the surrounding electrodes, which can cause nonadiabatic effects. In this work, we consider one of these effects, which consists in the emergence of a range of anode voltage values in which the monotonic growth of the pitch factor stops. The results of trajectory analysis using current tube and discrete source methods based on the ANGEL software package are presented, as well as an assessment of the influence of a magnetic lens on the properties of an electron beam based on a simple analytical model.

Development and research of a slow-wave system for a miniature W-band multibeam traveling wave lamp

The results of the development of a meander-type slow-wave system (SS) with metal supports for a miniature high-power W-band traveling wave lamp (TWT) with two ribbon electron beams are presented. Using a three-dimensional finite element software package, the electrodynamic parameters of the GS were studied. A two-section model of a TWT amplifier with a discontinuity has been developed to prevent self-excitation. Three-dimensional modeling of electron-wave interaction was carried out. It was found that with a total beam current of 200 mA in linear mode, the gain exceeds 30 dB in the frequency band 95.4...97.75 GHz, and the output power in saturation mode reaches 120 W. A technology for manufacturing SS based on laser microprocessing of thin copper plates is proposed. Test samples of the SS were manufactured and verified using optical and scanning microscopy.

Controlling the frequency of periodic self-modulation in gyrotrons with external reflections

We develop the theory of electron–wave interaction in gyrotrons with reflections of part of the radiation, focusing on the implementation of self-modulation generation regimes with controlled frequencies. The optimal conditions for the simultaneous excitation of neighboring axial modes of the electrodynamic system of a gyrotron with a reflecting diaphragm in the output waveguide path are found. When the gyrotron is powered by an electron beam under these conditions, periodic self-modulation regimes are realized with the distance between the main spectral components controlled by varying the distance to the reflector. The conclusions of the theory are confirmed by the results of direct particle-in-cells simulation.

Kinetic Interaction between an Electron Flow with a Wide Velocity Spread and a Short-Adjusted Slipping Wave Pulse at the Cherenkov Resonance

In this study, kinetic interaction at the Cherenkov resonance between an electromagnetic wave pulse and a flow of electrons possessing a wide velocity spread at the scale of the characteristic range of the resonant electron wave interaction is considered. Due to the absence of a distribution function slope in the range of velocities corresponding to the electron wave’s resonance, an electron’s flow is a nearly stable media from the point of view of its interaction with a long enough wave pulse. In this paper, we explain our findings on the process of electron interaction with potential relief where the wave pulse is so short that the characteristic scale of the wave amplitude’s inhomogeneity and the profile of the potential relief is comparable to the wavelength. We show that if an appropriate slippage between the phase and group velocities of the wave is provided, then the reflection process of particles from “fast” and “slow” close-to-resonance velocity fractions becomes non-symmetrical. This can provide a mechanism of amplification of short intensive wave pulses with electron flows with very large velocity spreads.

Trajectory analysis in a collector with multistage energy recovery for a DEMO prototype gyrotron. Part III. Influence of the spent electron beam parameters

The influence of the spent electron beam parameters on the possibilities of multistage energy recovery in the prototype gyrotron developed for the DEMO project is determined. The characteristics of electrodes and magnetic coils in a collector with four-stage recovery were optimized considering the distributions of electrons' coordinates and velocities obtained as a result of calculating the electron-wave interaction in the cavity. In the trajectory analysis in the collector, a sectioned electron beam was used to suppress the negative influence of the bundles of a toroidal solenoid used to create an azimuthal magnetic field. The possibility of achieving the total efficiency of the gyrotron of approximately 78% was shown, which is close to the maximum total efficiency with ideal separation of electron fractions with different energies, with the current of electrons reflected from the collector not exceeding 1% of the total current of the electron beam. Keywords: Microwave electronics, gyrotron, electron beam, energy recovery.

Траекторный анализ в коллекторе с многоступенчатой рекуперацией энергии для прототипа гиротрона DEMO. Ч. III. Влияние параметров отработанного электронного потока

The influence of the spent electron beam parameters on the possibilities of multistage energy recovery in the prototype gyrotron developed for the DEMO project is determined. The characteristics of electrodes and magnetic coils in a collector with four-stage recovery were optimized considering the distributions of electrons' coordinates and velocities obtained as a result of calculating the electron-wave interaction in the cavity. In the trajectory analysis in the collector, a sectioned electron beam was used to suppress the negative influence of the bundles of a toroidal solenoid used to create an azimuthal magnetic field. The possibility of achieving the total efficiency of the gyrotron of approximately 78% was shown, which is close to the maximum total efficiency with ideal separation of electron fractions with different energies, with the current of electrons reflected from the collector not exceeding 1% of the total current of the electron beam.

Electron density variability in the day-side ionosphere of Mars: The role of gravity waves

ABSTRACTMars Atmosphere and Volatile EvolutioN (MAVEN) has observed oscillations in the density, velocity, and temperature of ionospheric plasma on Mars. Atmospheric gravity waves can be an underlying mechanism. We propose a linearized wave–electron interaction model adopting a Wentzel–Kramers–Brillouin approximation to explore the electron density variations in the Martian day-side ionosphere for two regions, which are dominated by crustal magnetic fields and horizontal draped interplanetary magnetic fields. Our model results reveal that the electron density fluctuations associated with the crustal magnetic fields and the draped magnetic fields range from ∼ 40 per cent to ∼ 83 per cent and ∼ 29 per cent to ∼ 125 per cent, respectively. The wave-induced vertical electron flux peaks occur in a region ranging from ∼ 115 km to ∼ 179 km altitude. These results are comparable to the satellite observations. We further investigate the effect of the Martian magnetic topology on the wave-induced electron fluxes and demonstrate that the electron motions associated with the propagating gravity waves can be significantly influenced by the magnetic field orientations. The wave-induced variations in the electron temperature, ion density, and magnetic field combined with a comprehensive gravity wave model will be studied in further work.

Exploration of a PBG-based cavity structure for a multiple-beam extended interaction klystron

The feasibility of a photonic band-gap (PBG)-based interaction structure was analytically explored for a multiple-beam extended interaction klystron amplifier. This configuration accrues the advantages of the multiple-defect PBG-based extended interaction structure and multiple-beam operation. The mode configurations were analysed through 3D electromagnetic simulation and the applicability of the photonic band-gap cavity was studied for the multiple-beam operation of an extended interaction klystron amplifier. A typical six-defect cavity operating at around 83 GHz was designed for electron–wave interaction at 2π mode with 6 electron beams each carrying 300 mA current at the accelerating potential of 16.5 kV. A particle-in-cell simulation shows that an output power of ∼2 kW is possible with electronic efficiency of around 6.7%. A frequency-scaled-down interaction structure at Ku-band was fabricated and cold measurements were carried out to ascertain the feasibility. The measured values of the frequency for various modes, loaded quality factor and 3 dB bandwidth were found to be within 0.36%, 5.3% and 4.07%, respectively, against those from the simulation.

Forward-wave enhanced radiation in the terahertz electron cyclotron maser

Based on the principle of electron cyclotron maser (ECM), gyrotrons are among the most promising devices to generate powerful coherent terahertz (THz) radiation and play a vital role in numerous advanced THz applications. Unfortunately, THz ECM systems using a conventional high-Q cavity were theoretically and experimentally demonstrated to suffer from strong ohmic losses, and, accordingly, the wave output efficiency was significantly reduced. A scheme to alleviate such a challenging problem is systematically investigated in this paper. The traveling-wave operation concept is employed in a 1-THz third harmonic gyrotron oscillator, which strengthens electron-wave interaction efficiency and reduces the ohmic dissipation, simultaneously. A lossy belt is added in the interaction circuit to stably constitute the traveling-wave interaction, and a down-tapered magnetic field is employed to further amplify the forward-wave (FW) component. The results demonstrate that the proportion of ohmic losses is nearly halved, and output efficiency is nearly doubled, which is promising for further advancement of high-power continuous-wave operation of the ECM-based devices.

A Test of Energetic Particle Precipitation Models Using Simultaneous Incoherent Scatter Radar and Van Allen Probes Observations.

Quantification of energetic electron precipitation caused by wave‐particle interactions is fundamentally important to understand the cycle of particle energization and loss of the radiation belts. One important way to determine how well the wave‐particle interaction models predict losses through pitch‐angle scattering into the atmospheric loss cone is the direct comparison between the ionization altitude profiles expected in the atmosphere due to the precipitating fluxes and the ionization profiles actually measured with incoherent scatter radars. This paper reports such a comparison using a forward propagation of loss‐cone electron fluxes, calculated with the electron pitch angle diffusion model applied to Van Allen Probes measurements, coupled with the Boulder Electron Radiation to Ionization model, which propagates the fluxes into the atmosphere. The density profiles measured with the Poker Flat Incoherent Scatter Radar operating in modes especially designed to optimize measurements in the D‐region, show multiple instances of close quantitative agreement with predicted density profiles from precipitation of electrons caused by wave‐particle interactions in the inner magnetosphere, alternated with intervals with large differences between observations and predictions. Several‐minute long intervals of close prediction‐observation approximation in the 65–93 km altitude range indicate that the whistler wave‐electron interactions models are realistic and produce precipitation fluxes of electrons with energies between 10 keV and >100 keV that are consistent with observations. The alternation of close model‐data agreement and poor agreement intervals indicates that the regions causing energetic electron precipitation are highly spatially localized.

Theory and Practice of Creating a Two Energy Outputs Magnetron

This paper presents the methodology for 3-D simulation and design of the magnetron with two energy outputs. The principal functionality of the modified magnetron, both theoretically and experimentally, has been determined. The central distinguishing feature of this magnetron (for example, unlike the conventional magnetron with one output) is the availability of second energy output in the anode block. The mathematical models of both the resonant anode block and the electron-wave interaction are described. The dispersion characteristics of the anode block for cavities various geometries are given. It is supposed that forming the total RF field in the interaction space results from the interference of RF fields excited severally in the resonant anode block consisting of the small and large cavities (resonators). For PIC-simulation of electron-wave interaction in the dual-output magnetron, the non-linear system of equations is stated as a self-consistent system containing the equation of motion (for electron stream), the equation of excitation (for RF field), and Poisson’s equation for calculating the space-charge field. The fundamental feature of the self-consistent system of equations is a new algorithm for determining the Coulomb interaction forces. The implementation of the mathematical model made it possible not only to gain new knowledge about the physical processes in the magnetron but also to determine its output characteristics. On operating frequency of ∼ 13.34 GHz, at an anode voltage of 495 V, a magnetic field of ∼ 0.25 T, and with air cooling of the magnetron, there were obtained the following limiting values: the RF output power of ∼ 14.6 W and the power conversion efficiency of ∼ 40.8%. The use of the second energy output allowed extending the magnetron’s functionality and implementing the modes of the frequency tuning (adjunction) and its stabilization. The simulation results are in good agreement with the experiment. To the 100th anniversary of magnetron

Experimental Implementation of the Method of Generation of a Sequence of Ultrashort Gigawatt Cherenkov Superradiance Pulses with a Nanosecond Repetition Period

A periodic sequence of ultrashort superradiance pulses during the current pulse of an electron beam with a duration of about 40 ns has been generated in an experiment with a relativistic backward-wave oscillator with wave reflectors at the edges of the electron–wave interaction region. The pulse repetition period has been specified by the electron–wave feedback time and is 5.9 ns, which corresponds to the repetition frequency of 170 MHz at a FWHM duration of about 0.8 ns. The frequency of microwave oscillations is 10 GHz. The peak power of pulses is 0.8–1.3 GW. The corresponding conversion coefficients defined as the ratio of the peak power of the ultrashort microwave pulse to the power of the electron beam are 0.7–1.2.

Calculation of electrodynamic characteristics and electron-wave interaction in gyrotron resonators based on the ANGEL software package

Calculation of electrodynamic characteristics and electron-wave interaction in gyrotron resonators based on the ANGEL software package

Millisecond observations of nonlinear wave–electron interaction in electron phase space holes

Electron phase space holes (EHs) associated with electron trapping are commonly observed as bipolar electric field signatures in both space and laboratory plasma. Until recently, it has not been possible to resolve EHs in electron measurements. We report observations of EHs in the plasma sheet boundary layer, here identified as the separatrix region of magnetic reconnection in the magnetotail. The intense EHs are observed together with an electron beam moving toward the X line, showing signs of thermalization. Using the electron drift instrument onboard the satellites of the Magnetospheric Multiscale mission, we make direct millisecond measurements of the electron particle flux associated with individual electron phase space holes. The electron flux is measured at a millisecond cadence in a narrow parallel speed range within that of the trapped electrons. The flux modulations are of order unity and are direct evidence of the strong nonlinear wave–electron interaction that may effectively thermalize beams and contribute to transforming directed drift energy to thermal energy.

Generation in the regime with three resonance frequencies

If the group velocity of the wave is close to the bunch velocity, the bunch placed in the maximumum of the radiated pulse. It provides high effeciency of the electron-wave interaction. However, there are other factors related to particle dynamics, which have strong influence on the radiation process. In this paper the regime with three resonance frequencies is discussed. By varying the phase size of the electron bunch, the generation conditions at each of the frequencies can be changed. There are results for the spontaneous coherent super-radiative undulator emission in the terahertz frequency range from a short (as compared to the wavelength of the radiated wave) dense electron bunch. As a result, an electron bunch radiates two pulses with amplitudes of the radiated fields ∼ 10-70 MV/m.

Unifying Models of Chorus Wave Frequency Chirping

A new model of chorus wave electron interaction attempts to explain how observations can support two seemingly contradictory mechanisms of frequency chirping.

Amplification of a slipping quasi-monochromatic wave pulse by an electron flow with a wide velocity spread

Cherenkov interaction between a wave pulse and a flow of electrons possessing a very wide (on the scale of the characteristic band of the resonant electron–wave interaction) velocity spread is considered. We show that if the wave pulse is short enough, and its group velocity is close to the phase velocity, then the effect of the slippage of the resonant electrons with respect to the wave pulse leads to the transformation of an inert electronic medium into an active one (absorbing or amplifying the wave pulse, depending on the slippage sign). This can be a mechanism of formation of short powerful electromagnetic pulses as a result of amplification of short-pulse weak noises by electron flows which, due to natural reasons, have a large velocity spread, namely, electron flows in the magnetosphere of planets, in the plasma envelope of brown dwarfs and neutron stars, as well as in electron masers with weak electron–wave interaction (including ultra-relativistic electron beams used in free-electron lasers).

Stable Excitation of Higher Axial Modes in the Traveling-Wave-Tube Regime in Gyrotron Cavities With Additional Loss Elements

Weakness of the electron-wave coupling in compact low-power terahertz-frequency-range gyrotrons due to relatively low electron beam currents and operation at high cyclotron harmonics results in the use of long-length cavities with high diffraction Q-factors, and, therefore, with a high share of the ohmic loss of the radiated wave power. In this work, we demonstrate a possibility for stable operation at higher axial modes possessing relatively low diffraction Q-factors. Enhanced efficiency of the electron-wave interaction is provided due to the excitation of higher axial modes in the traveling-wave-tube regime.

Numerical Modeling of the Processes of Electron-Wave Interaction in the Cavities of High-Power Gyrotrons with a Frequency of 300 GHz

Numerical Modeling of the Processes of Electron-Wave Interaction in the Cavities of High-Power Gyrotrons with a Frequency of 300 GHz