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In order to improve the efficiency and obtain high output power with pure mode, 3-D particle-in-cell simulations are made on a novel coaxial triode vircator. Simulation results show that due to the appearance of the additional cylindrical cathode rod along the centerline, pure TM01 mode can be obtained in the output region. Simulation results also show that high-efficiency and pure TM01 mode output maintains even for output waveguide radius (equals anode radius) somewhat larger than the cutoff radius of the TM02 mode ( Rc,\mathrm {TM02} ). When the cathode and anode gap keeps unchanged, most optimal structure values can be scaled for models with different anode radius. By careful optimizations, the efficiency can reach 15% at an output power of 1.7 and 2.2 GW, respectively, for anode radii equal 5.6 and 6.6 cm ( < Rc,\mathrm {TM02} ); For anode radii equal 7.6 and 8.6 cm ( > Rc,\mathrm {TM02} ), the efficiency is about 13% at an output power of 2.5 and 2.9 GW, respectively. The operating frequencies all are about 3.6 GHz. [ABSTRACT FROM PUBLISHER]

A semitransparent cathode is proposed for an efficient operation of the relativistic magnetron (RM) with axial extraction. The semitransparent cathode is a kind of shaped cathode. It is achieved using a cylindrical cathode with longitudinal strips removed. The cross section of each removed strip is fan-shaped and all the emit strips are connected in the central area of the cathode. Results of the 3-D particle-in-cell simulations show that the using a semitransparent cathode yields similar performance benefits compared with that using the transparent cathode proposed by the University of New Mexico. Simulation results also show that output characteristics of the RM using the semitransparent cathode are insensitive to the depth and width of each cathode slot. Thus, the semitransparent cathode might be more robust for practical applications. [ABSTRACT FROM PUBLISHER]

An improved compact and high-efficiency A6 relativistic magnetron (RM) with axial extraction is proposed and studied by numerical simulations. Compared with the conventional design, two pairs of diametrically opposite cavities (four cavities) of the anode block are tapered onto the horn antenna for TE11 mode radiation with high output efficiency. Due to the cutoff radius of the TE11 mode is the smallest in the circular waveguide, the diameter of the output waveguide could be reduced obviously. And the total axial length of the horn antenna could also be shortened accordingly. At the same time, a semitransparent cathode is used for quick startup and efficient beam-wave interaction. Results of the 3-D particle-in-cell (PIC) simulations show that over 1.25 GW output power with TE11 mode is obtained at ${S}$ -band, when the electron beam voltage is 600 kV and the applied axial guiding magnetic field is 0.54 T. And the efficiency exceeds 66%. Simulation results also show that the output efficiency of the proposed RM keeps almost unchanged between 550 and 620 kV with fixed guiding magnetic field. [ABSTRACT FROM AUTHOR]

In this article, the influences of outgassing and flashover on the performance of a novel multipacting cathode are numerically investigated by using particle in cell-Monte Carlo collision (PIC-MCC) method, including the conditions of weak, medium, and strong outgassing. The numerical results demonstrate that under the condition of weak outgassing (0.1 Torr), multipacting is hardly influenced by gas ionization. Multipacting dominates the entire physical process. Due to the further improved output current by additional electrons generated from ionization, the weak outgassing can help cathode performance enhancement. Under the condition of medium outgassing (1 Torr), gas ionization first boosts multipacting developing and then tends to suppress multipacting process. During the initial stage, multipacting dominates the entire physical process. When multipacting tends to saturate, gas ionization will dominate the whole physical process. The rapidly increased output current will finally decrease gap voltage and induce the diode breakdown. Under the condition of strong outgassing (1 atm), multipacting is suppressed by gas ionization from beginning to end. Gas ionization dominates the whole physical process all the time. The strong effect of ionization collision will finally induce streamer discharge and diode breakdown. [ABSTRACT FROM AUTHOR]

The configuration design of a novel high-current density cathode for producing a ring-like electron beam is briefly introduced. Due to the complicated physical process of this novel cathode, in this paper, only the temporal evolution of multipacting on this cathode surface is numerically simulated by using the particle-in-cell method. The simulation results indicate that the multipacting process could be successfully achieved on the surface of this cathode. In multipacting process, both the electron number and output current start rapid exponential increases in very short time and then tend to be saturation with slow decreases. The multipacting start point is not at the triple-junction (vacuum-metal-dielectric) region but has a distance to the region. The saturation region of multipacting will expand toward the outlet with the spreading speed on the order of 107 m/s, which agrees with the speed of the luminous front of the initial surface flashover measured by experiment, and the emission current density of the cathode could reach the level of kA/cm2. The region of multipacting electrons will first be lengthened and then will be shortened due to the region of deposited positive charges expanding to the outlet and the maximum value of deposited positive charges moving from the triple-junction region to the outlet side. [ABSTRACT FROM AUTHOR]

The prototype and configuration design of a novel multipacting cathode producing a ring-like electron beam for high-current diode are presented. The whole dynamic process of the moving secondary electron on the multipacting cathode surface is theoretically investigated and numerically simulated using the Monte Carlo method. The results indicate that the prototype of the novel multipacting cathode for high-current diode is feasible. Under the interactions of the applied electric field (~MV/m) in axial and radial directions and the guiding magnetic field (~T) in axial direction, the seed electrons from the triple junctions move with spiral advancing trajectories along axial direction. Electron number can be effectively increased by each impact on the coating surface with high secondary electron emission yield coefficient. This phenomenon will achieve electron current amplification with the ring-like electron beam output till multipacting enters into saturation. The simulated characteristic parameters of the secondary electron and the working range of the multipacting cathode agree with the theoretical results. Under the typical condition, the moving distance of the secondary electron is on the order of submillimeters, the fight time is on the order of picoseconds, and the spread speed is on the order of 106 to 107 m/s. In addition, the multipacting saturation mechanism is analyzed, and the emission current density is roughly estimated to ~kA/cm2. Enhancing the magnitude of applied electric field in radial direction can effectively improve the emission current density. [ABSTRACT FROM AUTHOR]

This paper introduces a large-scale parallel 3-D fully electromagnetic particle-in-cell code named Nonlinear Evolution of Plasma-interaction Technology Under Nonneutral Environment—Three Dimensional (NEPTUNE3D) developed with the support of a parallel adaptive structured mesh application infrastructure JASMIN. NEPTUNE3D can be used to simulate beam–wave interactions in high-power microwave (HPM) generators. Some novel parallelization techniques are adopted in the NEPTUNE3D code for high parallel efficiency and good scalability. Some real-world HPM devices have been successfully simulated by NEPTUNE3D, such as the relativistic backward wave oscillator (RBWO), the magnetically insulated line oscillator (MILO), the virtual cathode oscillator, and the relativistic klystron amplifier. In this paper, two recent simulation examples are presented. The first is simulations of a knife-edge cathode RBWO, using 128 processors very efficiently. The second example is simulations of a MILO with a plate-inserted mode-transducing antenna, modeled using 27 million cells, 3 million particles, and 1024 processors with relatively high parallel efficiency. [ABSTRACT FROM PUBLISHER]