Search

A three-dimensional particle-in-cell (PIC) code, MAGIC3D, is used to simulate an A6 relativistic magnetron with metal tuner. As inserting six conducting rods into the resonators in regions where the RF magnetic field is high, the resonant frequency of 27[pi]-mode (n=6) of the A6 magnetron is tuned over the range from 4.27 to 4.47 GHz. The simulations show that with perturbed RF magnetic fields caused by metal tuner, the performance of the A6 magnetron in terms of radiation output power, frequency spectrum, and efficiency is superior compared with those using the uniform RF magnetic fields. Maximum output power of A6 with three tuners is 600 MW at 4.4 GHz, corresponding to a magnetron efficiency of 7.2%, which is about 20% higher than the conventional A6 magnetron where the axial external magnetic field is 5.5 kG and the beam voltage and the total current are 360 kV and 23 kA, respectively. When the tuner position of three metal rods is 8 cm, which is adjusted to get maximum power, a spectral amplitude in the [pi]-mode is lower 33 dB in power than the 2[pi]-mode. Index Terms--Relativistic magnetron, particle-in-cell, MAGIC3D

A highly reproducible, low-cost folded waveguide traveling-wave-tube amplifier is designed using the Pierce theory and a three-dimensional (3-D) particle-in-cell (PIC) code. The amplifier is designed to operate at 40-48 GHz with peak output radiation power of 200 W. Initial circuit parameters are obtained from the Pierce theory and circuit dispersion relations. A nonlinear large-signal performance of the amplifier is predicted from 3-D PIC simulations. Simulations show that the amplifier produces a saturated radiation power of 200 W at 44 GHz, corresponding to 5.6% electronic efficiency where the beam voltage and current are 21 kV and 0.17 A, respectively. A saturated 3-dB bandwidth is found to be 16% (40.5-47.5 GHz). Index Terms--Folded-waveguide traveling-wave tube (TWT), MAGIC3D, particle-in-cell code.

A high-power rising-sun magnetron oscillator (AX-9) operating at 9.50 GHz is examined by the use of a three-dimensional particle-in-cell (PIC) code, MAGIC3D. A mode spectrum of the 18 vanes rising-sun magnetron cavity is obtained from both an analytic field theory and the numerical code MAGIC3D. A large mode separation in the vicinity of a [pi]-mode is observed in the rising-sun configuration. A time evolved electron flow exhibits nine space charge spokes in the PIC simulations, which confirms the [pi]-mode oscillation in the 18 vanes rising-sun magnetron. When space charge spokes build up in the interaction region, a single frequency RF oscillation starts to grow and the leakage current escaping from the interaction region reduces to zero. Simulations predict that the saturated radiation power measured at the output waveguide is 250 kW at 9.50 GHz, corresponding to a magnetron efficiency of 53% where the external magnetic field is 0.52 T and the beam voltage and current are 28 kV and 17 A, respectively. Index Terms--MAGIC3D, particle-in-cell (PIC) code, rising-sun maguetron.

Experiments on a two-cavity gyroklystron amplifier are performed to demonstrate high power coherent radiation amplification at 34.95 GHz. Experiments show a saturated efficiency of 37%, a bandwidth of 0.36%, and a gain of 23.6 dB corresponding to peak radiation output power of 210 kW. Experimental results are in good agreement with large signal simulations. Calculations also show that a stagger-tuned three-cavity circuit increases the bandwidth to more than 0.9%. Index Terms - Cavity, coherent radiation, electron beam, gyroklystron.

Electron beam velocity spread influences the instantaneous bandwidth of a two-stage tapered gyrotron travelling wave tube amplifier. During the velocity spreads, the electron phase-mixing induces frequency-dependent sharp gain dip in the amplifier. The changes in the magnetic field profile, circuit length, velocity spread, and the beam axial velocity cause shifting or lowering of the gain dips. An analytical expression reveals the correlation between these parameters and bandwidth.

A stable uniform long-slit atmospheric argon plasma is produced by coupling a longitudinal-section electric (LSE) mode in a dielectric-loaded rectangular waveguide. The microwave-induced plasma discharge system consists of a 2.45-GHz microwave source, a circulator, a three-stub tuner, a transformer, and a tapered rectangular waveguide loaded with two dielectric slabs. A uniform 98-mm-long atmospheric argon plasma is observed at a relatively low microwave power level of 350 W and a gas flow rate of 10-15 L/min. Index Terms--Atmospheric plasma discharge, dielectric-loaded rectangular waveguide.

An X-band microwave amplifier module consisting of a low-noise solid-state amplifier and a low-gain helix traveling-wave-tube (TWT) is designed and fabricated. Measured microwave characteristics are found to be significantly improved compared with conventional helix-TWTs. Index Terms--Microwave power module (MPM), noise figure, traveling-wave-tube (TWT).