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The possibility of forming helical electron beams (HEBs) for multi-mirror and multi-barrel gyrotrons using systems with non-adiabatic injection of an electron beam into a magnetic field is analyzed. Systems where emission comes from circular arcs or from individual emission circles are considered. The possibility of implementing a HEB with a large (1.5–1.8) pitch factor, an acceptable velocity spread and a reduced influence of particles reflected from the magnetic mirror on the quality of the beam has been studied. [ABSTRACT FROM AUTHOR]

We have developed a method for calculation of the pulsed magnetic field in a sophisticated system of solenoids powered by time-shifted current pulses. The method served as the basis for analysis of the temporal dynamics of magnetic-field variations both in the region of formation of the helical electron beam, and in the space of its interaction with the microwave field in a relativistic gyrotron. It is shown that at some time instants, the degree of the field nonuniformity in the operating space of the gyrotron can reach 20%. The time interval is found, during which the magnetic field in the cavity is uniform. In the experimental process, this allows one to determine the time instant at which a high-voltage pulse is fed in for generation of microwave radiation. The calculated distributions of the magnetic field are compared with the experimental data. We have also developed a method for calculation of the time evolution of the parameters of a helical electron beam formed by a magnetron-injection gun with a pulsed magnetic field, calculated the velocity distribution in the electron beam, and found the time interval, during which a beam with the parameters acceptable for generation is formed. [ABSTRACT FROM AUTHOR]

We analyze theoretically and model a generator of a periodic sequence of ultrashort microwave pulses in a scheme with two coaxial cylindrical electron beams formed by the "Saturn" accelerator (Institute of Applied Physics of the Russian Academy of Sciences). An external cylindrical beam, as it moves rectilinearly along a periodic slow-wave system, ensures amplification of the radiation, whereas the internal near-axis beam ensures nonlinear cyclotron absorption. The modeling includes both the electron wave interaction and the formation of two electron beams in a common cathode unit, as well as their transportation in a common vacuum volume. It is shown that at a voltage of 210 kV and currents of 6.0 A and 4.4 A of the amplifying and absorbing beams, respectively, generation of 8-mm pulses with a duration of 650 ps, a peak power of 540 kW, and a repetition rate of 3.3 ns is possible. [ABSTRACT FROM AUTHOR]

Planar magnetron-injection gun forming a powerful (3 MW) sheet helical electron beam (HEB) for 140 GHz gyrotron was designed. Modified scheme of an electron beam analyzer based on the retarding electric field method was developed to measure the electron beam characteristics, including pitch-factor and velocity spread. Experimental results are in good agreement with theoretical predictions and demonstrate feasibility of formation of a wide (20 mm) sheet HEB with an energy of 100 keV, a current of 30 A and a pitch-factor of above 1.2 – 1.3. [ABSTRACT FROM AUTHOR]

We have developed a method for optimization of a planar magnetron-injection gun (MIG) with allowance for the three-dimensional configuration of the electron-optical system and the electron drift in crossed fields, which is transverse to the direction of the translational beam propagation direction. Recommendations are given on how to minimize the spread of transverse velocities with retaining the pitch factor, which is acceptable for efficient electron-wave interaction. The influence of roughness of the emission surface on the parameters and the operation regime of the planar MIG is studied. The optimal electrode configurations of a planar MIG have been found for a gyrotron with an operating frequency of 140 GHz at the first cyclotron-frequency harmonic with an accelerating voltage of 50 kV, a current of 30 A, and a magnetic-field compression of 36. These confirm good electric strength of the gun and manufacturability of the design of the planar electron-optical system. The obtained calculated distribution of the transverse velocities in a ribbon helical electron beam ensures the possibility of selective excitation of the high-order working mode TE11, 1 of a planar electrodynamic system and an output radiation power of several hundreds of kilowatts. [ABSTRACT FROM AUTHOR]

This paper presents the results of simulation of a collector with a four-stage recovery of the residual beam energy for a prototype gyrotron developed for the DEMO project. For spatial separation of electrons with different energies, an azimuthal magnetic field created by a toroidal solenoid is used. An increase in the recovery efficiency and a decrease in the electron flux reflected from the collector is achieved by reducing the spread of the radial position of the leading centers of electron trajectories at optimal parameters of the toroidal solenoid, as well as by using a sectioned electron beam. Trajectory analysis of the spent beam with electron distributions over the velocity and coordinate components close to those obtained in experiments with high-power gyrotrons showed the possibility of achieving a total efficiency of the gyrotron of more than 80%, which is close to the maximum efficiency with ideal separation of fractions of an electron beam with different energies. [ABSTRACT FROM AUTHOR]

A magnetron-injection gun able to provide very high ratio tj≈ 0.5 of the beam current to the Langmuir current has been designed, while maintaining good enough quality and stability of a formed helical electron beam. The specific feature of the gun is the shape of the cathode with two singular points of the electric field distribution which ensure close to uniform electric field profile within the emitter ring for wide range of operating currents. The gun provides the smoothed dependence of the beam parameters for currents up to 1.5–2 A and is suitable for wide (~ 10 GHz) frequency range gyrotron operation with the central frequency of 0.2 THz and output power ~ 1 kW within the whole tuning band. Such approach for the magnetron-injection gun design can be used for development of other promising high power sub-THz gyrotrons. [ABSTRACT FROM AUTHOR]

Coherent subterahertz radiation in the continuous-wave regime was obtained in a large-orbit gyrotron (LOG) operated at a high harmonic of the cyclotron frequency. An electron–optical system containing a gun with a cusp followed by a section of adiabatic magnetic compression with a factor of 1000 ensures the formation of a 30 keV/0.7 A helical axis-encircling electron beam with acceptable velocity spread and pitch factor in a magnetic field of 5 T. Stable singlemode operation was obtained at frequencies of 0.394 and 0.267 THz with radiation powers of 0.37 and 0.9 kW at the third and second cyclotron harmonics, respectively. Tuning of the generation frequency in the gyrotron during its operation at the second cyclotron harmonic and complex regimes of competition of two waves excited at the second and third cyclotron harmonics are also studied. [ABSTRACT FROM AUTHOR]

We develop the concept of a continuous wave (CW) 1.185 THz (wavelength about 250-μm) gyrotron with an output power of several watts, intended for dynamic nuclear polarization (DNP)/nuclear magnetic resonance (NMR) spectroscopy applications. For a 15-T magnetic field provided by a commercially available cryomagnet, the required frequency can be achieved by operating at the third cyclotron harmonic. Under conditions of extreme density of the mode spectrum, we propose using interaction with an electron beam intentionally formed with a high (up to 40%) velocity spread as a selection mechanism. This ensures suppression of the most dangerous parasitic traveling modes at the first and the second cyclotron harmonics, which are very sensitive to the spread. The main parameters of the gyrotron are determined both using the start currents analysis and within the framework of a nonstationary self-consistent model. Experimental feasibility of the single-mode third-harmonic generation under conditions of mode competition is verified based on 3-D particle-in-cell (PIC) simulations. [ABSTRACT FROM AUTHOR]

The design of a magnetron-injection gun (MIG) suitable for using in the CW 3-rd harmonic gyrotron with an output frequency of 1.185 THz and an output power about 100 W, intended for DNP/NMR spectroscopy applications is described. To improve the mode selection, several electron optics schemes are investigated. The MIG allows using both single-beam and double-beam schemes of the gyrotron operation with two different operating modes. Requirements for the electron beam parameters were found. The design of the triode MIG forming two generating beams with a quality suitable for 3-rd harmonic operation is suggested and optimized. The specific feature of the MIG is the possibility to form either two beams or one beam using the same electrode geometry and different number of emitting rings. The suggested MIG is not sensitive to small misalignment and reasonable manufacturing errors. A key feature of the design is that to improve the mode selection an electron beam with increased velocity spread is proposed. It is shown that it is possible to form two beams with practically equal and quite high pitch factors in all range of operating currents and at the same time small enough coefficient of reflection from the magnetic mirror in spite of large enough value of velocity spread. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of simple self-consistent theory data and experimental results aimed to study the influence of the anode voltage on the frequency of the subterahertz gyrotron with the goal of frequency stabilization. Numerical simulations of the electron beam formation and beam-wave interaction in a 0.26 THz gyrotron are performed. The experimental dependence of the gyrotron frequency tuning on mod-anode voltage is in agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

We study theoretically the possibilities of double-stage energy recuperation in a double-beam terahertz gyrotron. Numerical modeling, which was performed for a gyrotron producing radiation with a frequency of 0.78 THz and operating at the second cyclotron-frequency harmonic at the TE8.5 mode, demonstrates the possibility of spatial and energy separation of electron beams. This makes it possible to implement a double-stage recuperation scheme. The found energy spectra of electrons suggest an increase in the gyrotron efficiency by 3.5–4 times. [ABSTRACT FROM AUTHOR]

Coherent subterahertz radiation is achieved in an electron cyclotron maser (large-orbit gyrotron configuration) operating at a higher cyclotron harmonic in the continuous-wave generation regime. This auto-oscillator is based on the use of a gun with a magnetic field cusp and a section for adiabatic magnetic compression with a factor of 1000, forming a 30 keV/0.7 A axis-encircling electron beam in a magnetic field of 5 T. A stable single-mode generation is achieved in the case of operation at the third and second cyclotron harmonics at frequencies of 0.394 THz and 0.267 THz with radiation powers of 0.37 kW and 0.9 kW, respectively. [ABSTRACT FROM AUTHOR]

We perform three-dimensional numerical simulation of the electron-optical system (EOS) with the reversed magnetic field, which is designed for a large-orbit gyrotron (GBO) operated in a wide frequency range of 0.26-0.65 GHz, within the framework of a static model and analyze the influence of perturbations in the axial symmetry of electrodes and the magnetic field on the parameters of the axis-encircling electron beam. It is shown that the most significant perturbation of the parameters of the helical electron beam (HEB) is determined by the radial displacement of the cathode and the tilt of the cathode coil, which ensures the reversal of the magnetic field. Analytical estimations are presented, which allow determining the corresponding margins for the development of such systems. [ABSTRACT FROM AUTHOR]

We present the results of the theoretical and experimental studies, which are aimed at developing pulsed gyrotrons with relativistic electron beams operating in the millimeter-wavelength range and retaining the multimegawatt power level. The use of the interaction at the second gyrofrequency harmonic, which is characterized by a sufficiently high efficiency and availability of the solution for the mode selection problem, allows one to double the generation frequency without increasing the magnetic field. In the corresponding experiment, the output radiation power exceeded 2 MW, and the efficiency was about 30% at a wavelength of 5.5 mm. [ABSTRACT FROM AUTHOR]

The evaluation, design, and simulations of two different electron guns generating the beams for W-band second cyclotron harmonic gyro-TWTs forming a high-gain powerful amplifier cascade are presented. The optimum configurations of the systems creating nearly axis-encircling electron beams having velocity pitch-factor up to 1.5, voltage/current of 40 kV/0.5 A, and 100 kV/13 A with acceptable velocity spreads have been found and are presented. [ABSTRACT FROM AUTHOR]

We describe specific features of modeling numerically the operation of magnetron-injection guns, which form high-quality helical electron beams in gyrotrons operated in the short-wave part of the millimeter-wave band (at a wavelength of 1 mm). As an example, we consider the gun of a gyrotron having an operating frequency of 263 GHz designed for spectroscopic research. It is shown that there are good reasons to perform calculations and optimization of the magnetroninjection un in two steps. At the first step, a simplest two-dimensional model can be used, which allows only for the influence of the field of the electrodes and the intrinsic space charge of the beam on the beam parameters. At the second, final stage one should allow for such factors as roughness of the emitting surface and thermal velocities of electrons. The electron distribution function in oscillatory velocities and the coefficient of electron reflection from the magnetic mirror should be calculated. It is demonstrated that the magnetron-injection gun, which is optimized by the method presented, is sufficiently universal and can be operated both at the first and second cyclotron-frequency harmonics. This opens up the possibility of developing gyrotrons for spectroscopy applications at frequencies of 263 and 526 GHz, respectively, which are required for biological and medical research. [ABSTRACT FROM AUTHOR]

We solve analytically the problem about ion compensation for the space charge of a helical electron beam in a gyrotron operated in the long-pulse regime. Elementary processes, which take place during ionization of residual gas in the tube under typical pressures of 10-10 mm Hg, are considered. It is shown that distribution of the space charge is affected mainly by the electrons of the initial beam and slow-moving ions produced by ionization of the residual gas. Steady-state density of ions in the operating space of the gyrotron after the end of the transitional processes is found, as well as the electron density profile in the channel of electron beam transportation. The results obtained allow us to evaluate the pitch-factor variations caused by partial compensations for the potential 'sagging' in the gyrotron cavity, thus being useful for analysis of starting currents, efficiency, and mode competition in high-power gyrotrons. [ABSTRACT FROM AUTHOR]

Comprehensive optimization of the output efficiency of the gyrotron with a multistage system for energy recuperation is performed for the first time with allowance for the electron-beam interaction with the high-frequency field in the resonator and the subsequent deceleration of the beam in the presence of the electric field of the collector immersion lenses. The energy approach makes it possible to estimate the upper-bound limit of the efficiency. The effect of the ohmic loss on the efficiency of the gyrotron with recuperation is taken into account. The efficiency of the gyrotron working at the harmonics of the gyrofrequency with the two-stage recuperation can be increased to the levels typical of the magnetron technological complexes with a simultaneous increase in the working frequency of the sample heating by at least an order of magnitude. [ABSTRACT FROM AUTHOR]

We present the results of based on the PIC method numerical simulation of the dynamic processes of trapping of electrons into the adiabatic trap of a technological gyrotron for different configurations of the electric and magnetic fields in the electron beam formation region. The electrode geometry providing a low reflection coefficient of the magnetic mirror to suppress oscillatory modes in the space-charge cloud and ensure the stability of the electron beam with a high fraction of oscillatory energy in such a system has been found. [ABSTRACT FROM AUTHOR]

The opportunity of generating ribbon-shaped polyhelical electron beams intended to excite oscillations in the new type of gyrotrons is investigated via particle-in-cell simulation. Its distinctive features are the planar geometry of an interaction space and transverse energy extraction (with respect to the direction of translational motion of a helical electron beam). The electrode configuration has been found in the gyrotron with an operating frequency 75 GHz, where the formed electron beam has a velocity spread of ∼10%, the rotational energy fraction is 50%, and the beam profile is weakly distorted. When the voltage is 12 kV and the beam current is 1 A, the electron beam under study is demonstrated to excite the single-mode generation with an efficiency of up to 15% in the gyrotron's operating space produced by the planar waveguide. [ABSTRACT FROM AUTHOR]

The concept of a continuous wave 1-kW/1-THz gyrotron operated at the third cyclotron harmonic of the transverse electric TE9,7 operating mode has been developed. To suppress the mode competition effects in a terahertz gyrotron, we propose a scheme with two generating helical electron beams (HEBs) formed in a double-beam triode magnetron-injection gun (MIG), where both emitters of the electron beams are located on a common cathode of the conventional MIG. An optimal geometry of the MIG electrodes is found. It is shown that in a proposed scheme two HEBs having close pitch factors and a moderate velocity spread can be formed. This makes them suitable for high-efficiency single-mode generation in the high frequency gyrotron at high harmonic. [ABSTRACT FROM AUTHOR]

A method of synthesis of current-voltage characteristics (CVC) and calculation of the parameters of a helical electron beam (HEB) at the leading edge of the accelerating voltage pulse for gyrotron electron guns is proposed. These data can be used for a study of the gyrotron startup scenario with the mode competition taken into account. As an example, the results of calculations for a pulsed gyrotron with a frequency of 670 GHz are presented. [ABSTRACT FROM AUTHOR]

We describe the main stages of the development of a gyrotron in the sub-terahertz band with a power of several hundreds of kilowatts, a duration of the output radiation pulses of about 10 μs, and the generation frequency corresponding to an atmospheric transparency window. The gyrotron having a working frequency of 0.67 THz, a power of 200-300 kW, and the focal diameter of the output beam 1-2 mm can be used to detect sources of ionizing radiation from a distance of several tens of meters. The detection principle is based on the appearance of a microwave frequency discharge in the focal spot if the number of free electrons exceeds the natural background by 1-2 orders of magnitude. The electron-optical system of such a gyrotron has been calculated and optimized. The scenario of the gyrotron switch-on has been analyzed for the electron beam formed in such a system, and the possibility of stable single-mode generation on the TE mode is demonstrated. The results of analysis of thermal loads, which demonstrate their acceptable level in the cavity and the tube cavity for pulse durations of about 10 μs are presented. [ABSTRACT FROM AUTHOR]

A theoretical and experimental study of the oscillations of a space-charge cloud in a magnetron-injection gun of a powerful relativistic gyrotron has been performed. The charge storage occurs via electron-beam magnetic compression of the reflection of a part of the electrons having the highest transverse velocities from a magnetic mirror. It has been established that at high values of the compression coefficient the beam loses its stability that finally leads to the appearance of the beam current modulation at the frequency of the longitudinal oscillations of an electron beam in an adiabatic trap. According to the numerical simulations, the energy spread in the formed beam under these conditions reaches 4.6%, which is higher by an order of magnitude than that due to the space-charge effect in the beam transported along the metal tube. [ABSTRACT FROM AUTHOR]

The results of numerical analysis of the electron beam parameters influencing on the efficiency of energy recovery in gyrotrons are given. The weak dependence of minimal electron beam energy in collector region versus velocity distribution function is demonstrated. This fact may simplify the electron-optical system design of modern gyrotrons. [ABSTRACT FROM AUTHOR]

We consider the features of a system for the formation of an electron beam in a continuouswave high-stability gyrotron at the second gyrofrequency harmonic with an operating frequency of 258 GHz. The problems related to the maintenance of the required beam parameters are analyzed. The procedure and results of numerical simulation of the electron gun and collector of the gyrotron are described. The influence of various physical factors on the characteristics of the electronoptical system of the gyrotron are studied. The design of the electron beam formation system is described along with the results of measuring its parameters. [ABSTRACT FROM AUTHOR]

We analyzed the process of stabilization of electron beam parameters in a gyrotron having a high value of the “cold” pitch factor (i.e., that found with no account for the field of the beam’s space charge), namely, g0 ≥ 2. Time dependences of the current entering the work space and of the space charge and potential at different cross sections of the beam, as well as electron velocity distributions in the work space, which correspond to various values of g0, are found. It is shown that for g0 increasing to values, at which intense oscillations of the potential and space charge develop in the beam due to reflections of some electrons from the magnetic trap, it turned out to be impossible to increase the working pitch factor further. [ABSTRACT FROM AUTHOR]

We present the results of experimental studies of submillimeter-wave gyrotrons, which were obtained in the Research Center for Development of Far-Infrared Region of Fukui University (Japan). Distinctive features of the systems forming helical electron beams in submillimeter-wave gyrotrons are described. The results of the theoretical studies, which were aimed at excitation of higher harmonics in submillimeter-wave gyrotrons, reducing the operating voltage, and creating devices with smooth wideband tuning of the generation frequency, are presented. It is shown that modern gyrotrons are capable of ensuring continuous-wave generation at the frequencies from 200 to 400 GHz at a power level of up to hundreds of watts, and up to tens of kilowatts in the pulse-generation regime. [ABSTRACT FROM AUTHOR]

We determine distinctive features of the systems forming helical electron beams (HEBs) for high-power pulsed gyrotrons operated in the submillimeter-wave range. It is shown that they are characterized by a nonparaxial magnetic field in the emitter region, short distances between the cathode and the cavity, and the necessity of supplementing the magnetic system with a cathode coil placed behind the emitter. In a diode-type magnetron injection gun, which forms a boundary beam with a power of up to 4 MW, one can obtain the HEB parameters which are acceptable for the gyrotron operation. [ABSTRACT FROM AUTHOR]

We present the results of experiments on the formation of a high-quality relativistic helical electron beam (HEB) in a magnetron-injection gun. It is shown that suppression of parasitic excitation of microwaves in the input part of the transportation channel allows eliminating high-voltage breakdowns in the gun and achieving greater beam compression. A modulation of the electron beam current at the frequency of longitudinal electron oscillations between the cathode and the magnetic mirror in the trap, which is related to the instability of the helical electron beam, has been observed for the first time. The modulation depth can reach tens percent. Pickup of reflected electrons by a special diaphragm makes it possible to increase the achievable pitch factor, eliminate the beam-current modulation and, as a result, form although with a current loss on the diaphragm, an HEB with record-breaking values of the pitch factor, which exceed 2. For a moderate HEB compression, when the portion of reflected electrons is relatively low, their pickup by the diaphragm allows one to form a beam in which the total energy of the transverse motion of electrons conserves despite the loss of part of the current. After the optimization, a beam with an electron energy of 300 keV, a current of 100 A, a pitch factor of 1.5, and a velocity spread of 20% is obtained for a 15% loss of the current on the diaphragm. [ABSTRACT FROM AUTHOR]

We analyze the process of stabilization of electron beam parameters in a gyrotron for different profiles of the front of the accelerating-voltage pulse and the case of a large space charge trapped in the adiabatic trap. The duration of the portion of the pulse front, within which the electrons are reflected from the magnetic mirror and trapped, is at least an order of magnitude shorter than the entire length of the pulse front and is comparable with the characteristic time of potential oscillation development in the trap at great values of the pitch factor. The results of numerical analysis of the electron beam within the framework of models with finite durations of the voltage pulse front and instantaneous switch-on of the voltage showed that the steady-state values of the beam parameters are only weakly dependent on the pro.le of the pulse front. [ABSTRACT FROM AUTHOR]

We propose a method of increasing the pitch factor and decreasing the spread of rotational velocities of helical electron beams (HEBs) formed in nonadiabatic magnetron-injection guns of gyroresonant devices. The method is based on the effect of a special diaphragm mounted at the starting point of the transport channel on the process of formation of the laminar electron beam. The diaphragm located at one of the trajectory minima has such a diameter that it cannot be bent around by electrons with minimum rotational velocities. Such electrons land on it, whereas the remaining electrons pass further, moving in an increasing magnetic field. Then the electrons with the maximum rotational velocities reflect from the magnetic mirror adiabatically and land on the other side of the same diaphragm. Thus, the electron beam in the cavity contains electrons with a smaller resulting spread of rotational velocities. In the region of the HEB formation, the accumulation of the space charge of reflected electrons is eliminated, and the shielding of the electric field at the cathode is reduced, which eventually leads to an increase in the HEB pitch factor. Using such a diaphragm in the regime of current limitation by the space charge, the HEB with a high pitch factor (about 1.4) and a velocity spread acceptable for gyrotron applications (lower than 30%) was formed. [ABSTRACT FROM AUTHOR]

We show that it is possible to increase significantly (up to one-half of the Langmuir value) the current of the electron beam in a magnetron-injection gun operated in the nonadiabatic regime of formation of a relativistic helical electron beam if the velocity spread is small. The obtained beam has a current of 200 A, a velocity spread of about 10%, a pitch factor of about 1, and an electron energy of 340 keV. [ABSTRACT FROM AUTHOR]

An electron–optical system generating a rectilinear or helical 250 keV/4 A/10 μs electron beam with a high compression factor is developed. For the former beam, a compression factor as high as 4400 and a current density of 25 kA/cm2 are achieved. In the process of forming the helical beam, the electrons rotating about the system’s axis (paraxial beam) acquire an initial velocity in a transverse magnetic field produced by a kicker. Their pitch factor is increased to a desired (operating) value in an adiabatically growing magnetic field. In tentative experiments with the helical beam in a large-orbit gyrotron, generation was obtained at the second cyclotron harmonic (223 GHz). © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

We develop a thermionic-emission electron-optical system forming a dense beam of electrons moving along helical trajectories round the axis of a gyrotron cavity. The maximum beam current is 4 A and the pitch-factor of electrons is 1.0 for a particle energy of 250 keV and a pulse duration of 10 µs. Using such a beam in a gyrotron operated at the third cyclotron harmonic, we obtain single-mode oscillation with a power of 10 µs in the TE3,8 and TE3,9 modes with frequencies 371 and 414 GHz, respectively. [ABSTRACT FROM AUTHOR]

We consider the design of a gyrotron with an operating frequency of 24 GHz and an accelerating voltage of about 5 kV and describe a nonadiabatic electron gun forming an electron beam with a pitch factor of 1.8 and a velocity spread of about 10%. Longitudinal distribution of high-frequency field in a cavity with a step is optimized by choosing the step height and length. The design value of the gyrotron output efficiency is 35% at the second gyrofrequency harmonic. [ABSTRACT FROM AUTHOR]

We describe a nonadiabatic electron gun operated in the mode of a currentconfined by spatial charge and intended for producing helical electron beams for high-power gyroresonantdevices.Results of numerical simulation of electron trajectories and electron-beam parameters arepresented. It is shown that for a high operating current, the pitch factor and the electronvelocity spread can be significantly better than in the conventional adiabatic systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An optoelectronic gyrotron system that makes it possible to efficiently heat a cathode by electrons reflected from a magnetic mirror has been developed. The parameters of the primary electron beam are retained at a level that is acceptable for efficient microwave power generation. The results of a trajectory analysis of electrons and the cathode temperature conditions are reported. The corresponding decrease in power and temperature of the cathode filament suggests a significant (severalfold) increase in the filament lifetime, which is one of the main parameters determining the device lifetime. [ABSTRACT FROM AUTHOR]

The paper presents the design of sub-THz gyrotron with field emitter and preliminary tests of its electron-optical system. In contrast with traditional tubes with thermionic cathodes, such a device can be switched on immediately, which looks promising for some applications. The theoretical investigation of mode excitation and results of trajectory analysis of the electron beam formed by the non-adiabatic electron-optical system are presented. The experimental tests of original field cathode confirm that it can stably operate at technical vacuum conditions inside the tube and provide beam current that exceeds starting current of operation mode. The output power of about 50 W at 0.5 THz has been predicted for obtained electron beam parameters. [ABSTRACT FROM AUTHOR]