Large-orbit Electron Research Articles

Design of a 1-THz Fourth-Harmonic Gyrotron Driven by Axis-Encircling Electron Beam

In this article, the design of a fourth-harmonic gyrotron with 1-kW-level output power at 1 terahertz (THz) is presented. A unique advantage of this design is that, with a well-optimized magnetic-cusp large-orbit electron gun, the designed gyrotron can operate from first-harmonic to fourth-harmonic in multiple discrete bands by varying the confining magnetic field strength. By carefully balancing the competing modes, the gyrotron can be tuned to operate at six candidate modes, including TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,2</sub> for fundamental harmonic, TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2,3</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2,4</sub> for second-harmonic, TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3,5</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3,6</sub> for third-harmonic, and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4,8</sub> for fourth-harmonic interactions. As the main operating mode, the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4,8</sub> can generate a peak output power of 1.68 kW, with an output efficiency of about 2.1%, and a magnetically controlled frequency tuning range of about 1.5 GHz around 1 THz. The impact of the longitudinal nonuniformity of the cavity at high-harmonic interaction was also studied. It shows that a radial tolerance of several micrometers will significantly elevate the start-oscillation current and deteriorate output performance. This design is to produce a THz source with ultra-wideband tuning capability ranging from the submillimeter-wave to 1-THz bands.

Terahertz Gyrotrons at High Cyclotron Harmonics with Irregular Electrodynamic Systems

Two experimental gyrotron test benches in the terahertz frequency range with large-orbit electron beams operating at high harmonics of the cyclotron frequency are created at the Russian Academy of Sciences’ Institute of Applied Physics. An overview is presented of work aimed at developing advanced irregular microwave systems for these gyrotrons. The aim of this work is to reduce ohmic losses and improve the selectivity of operating wave excitation at high harmonics.

PERMANENT MAGNET SYSTEM AND ELECTRON GUN DESIGN FOR A 3RD HARMONIC PENIOTRON

This study discusses the operating characteristics of a large-orbit electron gun and a corresponding permanent magnet system of a 3rd harmonic peniotron. After optimization, a novel axis-encircling electron beam with axial velocity spread 4.48%, guiding centre deviation ratio 6.97% and high velocity ratio 2.03 is obtained. Driven by the electron gun, an output power of 35.4 kW is obtained, and the device efficiency is up to 56.0%, which is an attractive result in laboratories. The main advantages of such a peniotron are its compact size and low cost, which can meet the needs of vehicle, airborne and other mobile devices. The numerical analysis reveals that the relative axial position between the electrode system and magnet system has a great influence on the device performance, which needs careful control and precise adjustment.

Design of a large-orbit electron gun with gradual reversal magnetic field for a W-band permanent magnet peniotron

This paper demonstrates the operating characteristics of an axis-encircling large-orbit electron gun and a corresponding permanent magnet system of a W-band peniotron. The practical novel large-orbit electron beam with axial velocity spread of 5.17%, transverse velocity spread of 1.28%, guiding center deviation ratio 10.7%, and high velocity ratio 2 is designed. The main advantages of such a peniotron in the large-orbit configuration with a permanent magnet system are its compact size, reduced operational gap, and lower cost. Critical characteristics, such as acceleration voltage and the relative axial position of the magnetic system and electrode system have also been well examined and it is shown that a careful control of them is important for the device performance.

High Power Wideband Gyrotron Backward Wave Oscillator Operating towards the Terahertz Region

Experimental results are presented of the first successful gyrotron backward wave oscillator (gyro-BWO) with continuous frequency tuning near the low-terahertz region. A helically corrugated interaction region was used to allow efficient interaction over a wide frequency band at the second harmonic of the electron cyclotron frequency without parasitic output. The gyro-BWO generated a maximum output power of 12kW when driven by a 40kV, 1.5A, annular-shaped large-orbit electron beam and achieved a frequency tuning band of 88-102.5GHz by adjusting the cavity magnetic field. The performance of the gyro-BWO is consistent with 3D particle-in-cell numerical simulations.

Generation of large-orbit electron beam using magnetron type injection gun

The generation of axis-encircling large-orbit electron beam using magnetron type injection gun is studied theoretically and numerically. Since the cathode emission band is parallel not only to the system’s axis but also to the magnetic field lines, it eliminates the initial angular momentum spread at the cathode and helps to reduce the velocity spread greatly. Through numerical simulation by EGUN, a large-orbit electron beam with axial velocity spread of 1.82%, guiding center deviation of 6.1%, and velocity ratio of 1.67 is obtained. By adjusting the voltages of the two anodes, the beam quality can be modulated easily to meet the specific requirements of different gyro-devices. The scheme provides a new electron gun candidate for the large-orbit devices.

Numerical study of an 8 mm third-harmonic peniotron with a gradual reversal of the magnetic field

A novel large-orbit electron gun with a gradual reversal of the magnetic field for the 8 mm third-harmonic peniotron is numerically studied in this paper. In the permanent magnetic condition, an electron beam with axial velocity spread of 4.78%, guiding center deviation of 7.18%, and velocity ratio of 2.2 is generated in the gun, satisfying the special requirements of beam-wave interaction in the third-harmonic peniotron. Compared with the traditional three stage method, it is unnecessary here to generate a thin tubular electron beam before the reversal point and the mutational distribution of reversal magnetic field. In addition, the emission band can be placed in the area of axial magnetic field where its magnitude decreases gradually, which reduces the structure complexity and the difficulties in tube-making process greatly. Finally, the peniotron is predicted to yield an output power of 31.9 kW at 30 GHz, with its microwave conversion efficiency of up to 49.4%, which shows the perfect matching between its high frequency system and its electron-optical system. According to the numerical calculations, the device performance is very sensitive to the relative axial position between the magnetic system and the electrode system. If the magnetic system shifts 0.8 mm to the right, the device efficiency would decrease from 49.4% to 31.7%. This phenomenon provides meaningful information in the device hot-test.

THz回旋自谐振脉塞多模束波互作用非线性模拟

A nonlinear description via the self-consistent coupling equations of waves with relativistic electron beam, is provided for the nonlinear interaction of multiple modes with the relativistic electron beam in cyclotron autoresonance maser(CARM), to analyze the mode competition in CARM. Specific analysis of a sub-terahertz (0.35 THz) CARM with higher-order mode TM51 and a large-orbit electron beam shows that, contrasted with, both larger output power and higher gain can be achieved for a CARM with TM operating mode. By optimizing parameters, the operating mode can play an absolutely dominant role while the competing modes are efficiently suppressed. However, a multi-mode nonlinear simulation must be performed for a higher-order terahertz CARM, because the output power is quite sensitive to the operating parameters.

8 mm三次谐波潘尼管大回旋电子枪设计

8 mm三次谐波潘尼管大回旋电子枪设计

大回旋半径电子枪渐变线圈磁场的设计及优化

大回旋半径电子枪渐变线圈磁场的设计及优化

Search for Superconductivity in Ultra-dense Deuterium D(−1) at Room Temperature: Depletion of D(−1) at Field Strength &gt;0.05 T

Ultra-dense deuterium D(−1) is expected to be both a superfluid and a superconductor as shown by recent theoretical research. Condensed D(−1) can be deposited on surfaces by a source which produces a stream of clusters. A magnetic field strongly influences the type of material formed. Very little of D(−1) and of the form D(1), which is strongly coupled to D(−1), exists on the magnet surface or within several mm from the magnet surface. Even the formation of D(−1) on the source emitter is strongly influenced by a magnetic field, with a critical field strength in the range 0.03–0.07 T. Higher excitation levels D(2) and D(3) dominate in a magnetic field. The excitation level D(2) is now observed for the first time. The removal of D(−1) and D(1) in strong magnetic fields is proposed to be due to a Meissner effect in long D(−1) clusters by large-orbit electron motion. The lifting of long D(−1) clusters above the magnet surface is slightly larger than expected, possibly due to the coupling to D(1). The previously reported oscillation between D(−1) and D(1) in an electric field is proposed to be due to destruction of D(−1).

A novel large-orbit electron gun with gradually-changing reversal magnetic field

A novel approach to achieve a large-orbit electron beam is demonstrated using a gradually-changing reversal magnetic field. On the basis of analyzing the general regularities of electron movement and various factors which lead to eccentricity and velocity spread in the gradually-changing reversal magnetic field, we design a large-orbit electron gun. Different from the traditional three-step method, our design does not pursuit the formation of thin tubular electron beam and the utilization of mutation reversal magnetic field, which reduces the difficulties in structure complexity and tube-making process. In addition, the cathode emission band can be placed in the axial magnetic field before the magnetic reversal point where its magnitude decreases gradually, by controlling the angular momentum difference between every trajectory starting points and using the offset effect of various unfavorable factors to reduce eccentricity and velocity spread. The simulation results are consistent with the theoretical analyses, which shows that the beam quality can be improved remarkably by fine-tuning electromagnetic fields, confirms that the efficiency and the applicability of the adjusting method we proposed, and provides a new technical way to obtain a high-quality large-orbit electron beam for high-efficiency large-orbit millimeter-wave devices.

A LARGE ORBIT ELECTRON GUN DESIGN FOR A TERAHERTZ HARMONIC GYROTRON

Design of an axis-encircling large-orbit electron gun for a terahertz harmonic gyrotron is presented. Based on a canonical momentum conservation theory, analytical calculations are carried out to determine critical electron gun parameters. This procedure provides a fast optimization process to determine electron gun parameters. The calculated results are compared with electron gun code.

A novel large-orbit electron beam generated by a Cuccia coupler for a Ka-band third-harmonic slotted peniotron

In this work, a novel large-orbit electron beam generated by a Cuccia coupler for a Ka-band third-harmonic slotted is proposed. The Cuccia coupler was originally used in the electron coupler for amplitude modulation and power control at ultrahigh frequencies. It is demonstrated by the 3D-PIC simulation that a 6 kV, 0.5 A beam will be gyroresonantly accelerated when a microwave power of 16 kW at 10 GHz is injected into the coupler, from which a 37 kV, 0.5 A large-orbit electron beam will be obtained; it is characterized by a relative velocity spread lower than 1% and a velocity ratio α (υ⊥/υz) up to 2.3. Moreover, other electron beam parameters including transverse velocity (υ⊥), longitudinal velocity (υz) and deviation of guiding center could be adjusted independently, whereas these are rather difficult for the cusp gun. Finally, the Ka-band third-harmonic slotted peniotron in 2π mode driven by such a beam is verified by 3D-PIC simulation, which is predicted to yield an output power of 8 kW at 30 GHz, with a microwave power conversion efficiency up to 50% and a device efficiency up to 43%, respectively.

Amplification of a fast wave by extracting both the kinetic energy and electrostatic potential energy of a large-orbit relativistic electron beam in a coaxial electrostatic wiggler

Nonlinear model and simulation technique of the interaction and energy transfer between a fast wave and a large-orbit relativistic electron beam in a coaxial electrostatic wiggler are presented. Unlike the situations in a magnetostatic-wiggler free-electron laser (MWFEL) and in an electron cyclotron maser (ECM), the electrostatic potential of the electrons plays an important role and participates in the energy exchange between the wave and the electron beam. Compared to MWFEL and ECM, the coaxial electrostatic-wiggler configuration has a distinguishing peculiarity that besides the electron-beam’s kinetic energy, its electrostatic potential energy can be effectively transferred to the fast wave. Simulation shows that wave could be amplified with ultrahigh gain by extracting both the kinetic energy and electrostatic potential energy of the electron beam.

Terahertz transverse-magnetic-wave cyclotron autoresonance maser with a large-orbit relativistic electron beam

The cyclotron autoresonance maser (CARM) operating in a transverse-magnetic (TM) wave by employing a large-orbit relativistic electron beam shows a peculiarity that the growth rate range of coherent amplification of the TM wave is split into two branches as the electrons' cyclotron frequency increases: the upper branch is quite favorable to terahertz operation, whereas the lower branch can lead to a backward-wave CARM mechanism which is suitable to sub-terahertz operation. Compared to a terahertz large-orbit transverse-electric-wave gyrotrons and gyro-amplifiers which are experimentally realized up to date, a terahertz large-orbit TM-wave CARM requires much lower operating magnetic field and allows the cavity to have larger transverse dimension.

Design and Numerical Optimization of a Cusp-Gun-Based Electron Beam for Millimeter-Wave Gyro-Devices

A novel thermionic cusp electron gun operating in the temperature-limited regime that produces a large-orbit electron beam through a nonadiabatic magnetic-field reversal was designed, analyzed, and optimized to give an electron-beam ideal for driving gyro-devices, particularly in the millimeter-to-submillimeter-wavelength range due to its small cross-sectional size. The annular-shaped axis-encircling electron beam had a beam current of 1.5 A at an acceleration potential of 40 kV, a tunable velocity ratio alpha (= vperp/vz) between one and three, an optimized axial velocity spread A.vx/vz of ~8%, and a relative alpha spread Deltakappa/alpha of ~10% at an alpha value of 1.65.

Mode competition in a large-orbit coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier

Physics issues of mode competition in a large-orbit coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier are investigated. It is shown that the use of a coaxial waveguide brings about two peculiarities: possible enhancement of the transverse dimensional size and the rarefied spectrum and that the applications of a large-orbit electron beam and CARM mechanism can efficiently exclude the parasitic effect of the cyclotron harmonics and spurious oscillations of undesired modes. The dispersion diagram and numerical simulation demonstrate that mode competition and spurious gyrotron-like or CARM-like oscillations can be suppressed when a large-orbit coaxial-waveguide CARM amplifier operates in a higher-order mode.

Large-orbit coaxial-structure cyclotron autoresonance maser

We present a conceptual proposal for a large-orbit coaxial-structure cyclotron autoresonance maser (CARM), wherein the rf structure is a coaxial waveguide or cavity and a large-orbit electron beam encircles the axis of the coaxial structure. Both dispersion analysis and nonlinear simulations demonstrate the feasibility of the proposal. The large-orbit coaxial-structure CARM could be expected to operate in millimeter and submillimeter wave ranges with high power, low operating magnetic field, and ultrahigh gain. It is found that electron-beam velocity spread substantially decreases the power of CARMs, but this adverse influence might be offset by a proper taper of the axial magnetic field.

Microwave Excitation by a Constrained Large-Orbit Electron Beam—A Unified Dispersion Relation for Slow- and Fast-Wave Devices

A unified linear dispersion relation that describes both slow- and fast-wave devices excited by a constrained large gyration orbit (LO) monoenergetic electron beam of infinitely small thickness has been derived and studied numerically. Beam electrons in a sufficiently long sinusoidally corrugated metal slow-wave structure are assumed completely neutralized by the background ions in equilibrium state. An exact dispersion relation of an LO backward-wave oscillator that can reasonably describe instabilities in the slow-wave device region has been obtained. A parameter a, defined as a ratio of the transverse to the longitudinal component of the electron velocity, is found to have a critical value above which the excitation of a nonaxisymmetric quasi-TE/sub 11/ mode caused by the fast cyclotron instability dominates the conventional Cherenkov instability. However, for an SWS having infinitely small amplitude of corrugation, radiation with w W is altogether suppressed; instead, an alternate mechanism, namely, Cherenkov instability in the azimuthal direction with w<W found first in the current paper leads to the excitation of microwaves. This suggests that the radiation from some previous CRM experiments with a high current density electron beam neutralized by ions might have been caused not by CRM instability but by the present Cherenkov instability in the azimuthal direction.