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Experiments have demonstrated high-power amplification (100 MW class) from a traveling wave amplifier driven by a modulated electron beam. The modulated electron beam is generated by applying a modulated voltage pulse from a nonlinear transmission line (NLTL) to the cathode of the electron gun. The system showed that over the designed operating range of the disk-on-rod (DoR) TWT amplifier (1.2–1.4 GHz), the peak frequency of the amplifier output tracked the peak frequency of the NLTL to within ±2%; however, the output was not phase stable. Measured RF energy gain for this frequency regime ranged from 1.5 at 1.2 GHz up to 5.0 at 1.4 GHz). [ABSTRACT FROM AUTHOR]

A set of three apparatus enabling RF exposure of aerosolized pathogens at four chosen frequencies (2.8 GHz, 4.0 GHz, 5.6 GHz, and 7.5 GHz) has been designed, simulated, fabricated, and tested. Each apparatus was intended to operate at high power without leakage of RF into the local environment and to be compact enough to fit within biocontainment enclosures required for elevated biosafety levels. Predictions for the range of RF electric field exposure, represented by the complex electric field vector magnitude, that an aerosol stream would be expected to encounter while passing through the apparatus are calculated for each of the chosen operating frequencies. [ABSTRACT FROM AUTHOR]

The recirculating planar crossed-field amplifier (RPCFA) was designed, constructed, and tested at the University of Michigan. The RPCFA was driven by a number of RF sources ranging in frequency from 2.40 to 3.05 GHz and powers of 1 to 800 kW. Pulsed voltage was delivered to the cathode by the Michigan electron long beam accelerator with ceramic insulator (MELBA-C) which was configured to supply pulses of −300 kV, 1–10 kA, with 0.3–1.0- $\mu \text{s}$ pulse lengths. The RPCFA demonstrated zero-drive stability and a bandwidth of 15%. Amplification of microwave signals, at the design frequency of 3 GHz, below 150 kW, was observed with a mean gain of 7.87 dB and high variability, $\sigma = 2.74$ dB. Filtering this data set to only include shots with identical voltage and current profiles yielded a gain of 6.6 ± 1.6 dB. The mean gain increased to 8.71 dB and the variability decreased to $\sigma =0.63$ dB when the injected microwave power increased beyond 150 kW. Peak output powers of nearly 6 MW were achieved with RF breakdown limiting the maximum output power of the device. [ABSTRACT FROM AUTHOR]

The harmonic recirculating planar magnetron (HRPM) is a frequency-agile, multispectral HPM source. The HRPM implements an $L$ -band oscillator (LBO) and an $S$ -band oscillator (SBO) near 1 and 2 GHz, respectively. The novel coaxial-all-cavity-extraction (CACE) method was implemented to extract power from the SBO. The two oscillators demonstrated harmonic frequency locking, where the SBO frequency locked to the LBO second harmonic frequency. The two oscillators are concluded to operate as a damped, driven, harmonic oscillator system. In the locked state, the LBO acts as the driving oscillator, the SBO acts as the driven oscillator, and the coupling mechanism between the two oscillators is the harmonic content in the electron spokes as they propagate directly from the LBO to the adjacent SBO. The two primary variables studied in this system are the LBO harmonic frequency and the SBO quality factor, $Q$. In isolated SBO experiments, the dominant operating state of the magnetron was the $5\pi $ /6 mode. However, when operated in tandem with the LBO, the SBO was forced to operate in the $\pi $ -mode. Output powers in HRPM experiments generated SBO powers of 9.5 ± 1.4 MW at high $Q$ , 19 ± 6 MW at moderate $Q$ , and 28 ± 9 MW at low $Q$. Output powers in the isolated SBO configuration were not significantly different from the HRPM. By experimentally manipulating the hub drift direction and altering the evolution of harmonic content received by the SBO, the locked state was significantly diminished, suggesting that the beam spokes play a crucial role. [ABSTRACT FROM AUTHOR]

The recirculating planar crossed-field amplifier (RPCFA) was designed and simulated using the finite-element frequency-domain code ANSYS HFSS and the particle-in-cell (PIC) code MAGIC. The RPCFA is a high-power microwave device adapted from the recirculating planar magnetron, developed at the University of Michigan, Ann Arbor, MI, USA. Electromagnetic (EM) PIC simulations of a planar, meander line, and slow wave structure demonstrated 13.5-dB amplification of a 1.3-MW, 3-GHz signal to approximately 29 MW. The RPCFA is designed to be driven by pulsed power from the Michigan electron long beam accelerator-ceramic insulator, which is currently configured to deliver pulses at −300 kV, 1–10 kA, with 0.3– $1~\mu \text{s}$ pulse lengths. The RF input-drive signal will be provided by an MG5193 magnetron which delivers 5- $\mu \text{s}$ pulses up to 2.6 MW at 3 GHz. EM PIC simulations also demonstrated zero-drive stability of the design and were used to evaluate changes in performance resulting from variations of several experimental parameters. Variation of the drive frequency suggested that the RPCFA is expected to have a 3-dB amplification bandwidth of 300 MHz or 10%. [ABSTRACT FROM AUTHOR]

Using measured waveforms from a synchronous-wave ferrite nonlinear transmission line (NLTL), particle-in-cell simulations demonstrate the potential to emit GW-class electron beams (hundreds of kilovolts, multiple kiloamperes) with current modulations as great as 30% of the average beam current, with modulations occurring at a peak frequency equal to that of the peak NLTL output frequency. The NLTL-modulated beam is then coupled to disk-on-rod slow wave structure (SWS) simulations in which it is shown that the extractable RF generated through interaction of the modulated beam with the SWS is up to ten times greater than that directly extractable from the NLTL itself. [ABSTRACT FROM PUBLISHER]

A high-power, pulsed operation, multibeam, S-band, coaxial disk-on-rod traveling-wave-tube amplifier has been simulated. In this paper, the amplifier, having an 81-period slow wave structure, utilized six 20-A beams. For 800 W input signals at frequencies between 2 to 4 GHz, gain and bandwidth values of 21.6 dB at 8% bandwidth and 15 dB at 15% bandwidth were observed for the beam voltages of 100 and 120 kV, respectively. [ABSTRACT FROM PUBLISHER]

A spatially dispersive nonlinear transmission line (NLTL) using axially biased ferrite as the nonlinear medium has been developed. The NLTL is frequency tunable from 0.95 to 1.45 GHz with adjustment of the axial biasing field. A circuit model describing the dispersion of the line has been developed and compared with experimental measurements and time and frequency domain simulations. Instantaneous peak power levels exceeding 100 MW and average power levels of 10s of MW with durations from 4 to 17 ns have been observed. [ABSTRACT FROM PUBLISHER]

A compact axial \pi-mode extraction scheme, which is based on a patent by Greenwood, is demonstrated in conjunction with the UM/L-3 relativistic magnetron using the particle-in-cell code ICEPIC. Cases utilizing Greenwood's extraction technique were compared with power extraction using traditional radial waveguides. Average extracted power values in all simulated axial cases were found to be within +/-6.5% of the radial cases. Cases utilizing 85 ^\circ and 90^\circ sector waveguides were found to have efficiencies up to ten percentage points higher than the radial case. The best performing case was found to use a set of three axially oriented 90 ^\circ sector waveguides, shorted on the upstream side, with the short located 15 cm from the center of the magnetron apertures. [ABSTRACT FROM PUBLISHER]

Rapid startup, increased pulsewidth, and mode locking of magnetrons have been explored experimentally on a relativistic magnetron by radio frequency (RF) priming. Experiments utilize a -300 kV, 2-8 kA, 300-500-ns electron beam to drive a Titan six-vane relativistic magnetron (5-100 MW output power in each of the three waveguides). The RF priming source is a 100-kW pulsed magnetron operating at 1.27-1.32 GHz. Tuning stubs are utilized in the Titan structure to adjust the frequency of the relativistic magnetron to match that of the priming source. Experiments are performed on rising sun as well as standard anode configurations. Magnetron start-oscillation time, pulsewidth, and π-mode locking are compared with RF priming versus the unprimed case. The results show significant reductions in microwave output delay and mode competition even when Adler's Relation is not satisfied. [ABSTRACT FROM AUTHOR]