Microwave pulse compression using a helically corrugated waveguide

There has been a drive in recent years to produce ultrahigh power short microwave pulses for a range of applications. These high-power pulses can be produced by microwave pulse compression. Sweep-frequency based microwave pulse compression using smooth bore hollow waveguides is one technique of passive pulse compression, however, at very high powers, this method has some limitation due to its operation close to cutoff. A special helical corrugation of a circular waveguide ensures an eigenwave with strongly frequency dependent group velocity far from cutoff, which makes the helically corrugated waveguide attractive for use as a passive pulse compressor for very high-power amplifiers and oscillators. The results of proof-of-principle experiments and calculations of the wave dispersion using a particle in cell particle-in-cell (PIC) code are presented. In the experiments, a 70-ns 1-kW pulse from a conventional traveling-wave tube (TWT) was compressed in a 2-m-long helical waveguide. The compressed pulse had a peak power of 10.9 kW and duration of 3 ns. In order to find the optimum pulse compression ratio, the waveguide's dispersion characteristics must be well known. The dispersion of the helix was calculated using the PIC code Magic and verified using an experimental technique. Future work detailing plans to produce short ultrahigh power gigawatt (GW) pulses will be discussed

Giant half-cycle attosecond pulses

Half-cycle picosecond pulses have been produced from thin photo-conductors, when applying an electric field across the surface and switching on conduction by a short laser pulse. Then the transverse current in the wafer plane emits half-cycle pulses in normal direction, and pulses of 500 fs duration and 1e6 V/m peak electric field have been observed. Here we show that single half-cycle pulses of 50 as duration and up to 1e13 V/m can be produced when irradiating a double foil target by intense few-cycle laser pulses. Focused onto an ultra-thin foil, all electrons are blown out, forming a uniform sheet of relativistic electrons. A second layer, placed at some distance behind, reflects the drive beam, but lets electrons pass straight. Under oblique incidence, beam reflection provides the transverse current, which emits intense half-cycle pulses. Such a pulse may completely ionize even heavier atoms. New types of attosecond pump-probe experiments will become possible.Comment: 5 pages, 4 figures, to be presented at LEI2011-Light at Extreme Intensities and China-Germany Symposium on Laser Acceleratio

Microwave pulse compression using helically corrugated waveguides and its potential for generating ultra-high power RF radiation

The use of a helically corrugated waveguide as a dispersive medium for microwave pulse compression will be presented. The helically corrugated waveguide has a large variation in group-velocity with frequency, in a region far from cut-off. This compressor does not suffer from reflections associated with operation near to cut-off and therefore can be used at the output of a high-power microwave device. © 2004 IEEE

A co-harmonic gyro-monotron with a novel corrugated interaction cavity

A novel interaction cavity has been designed for a gyro-monotron, allowing co-harmonic generation at the 2nd and 4th harmonic resonances of the cyclotron frequency. The output aperture of the cavity has been designed to trap the lower harmonic, whilst allowing output of the upper harmonic. Results from recent numerical simulations, performed using MAGIC 3-D, are presented. The intended co-harmonic behaviour is observed, with simultaneous excitation of the 2nd and 4th harmonics. Refinement of the output structure is now being undertaken to ensure only the 4th harmonic signal is emitted

A co-harmonic gyro-oscillator with a novel interaction cavity

A novel interaction cavity has been designed for a gyro-oscillator, allowing co-harmonic generation at the 2(nd) and 4(th) harmonic resonances of the cyclotron frequency. The output aperture of the cavity has been designed to trap the lower harmonic, whilst allowing output of the upper harmonic. Results from recent numerical simulations, performed using MAGIC 3-D, are presented. The intended co-harmonic behaviour is observed, with simultaneous excitation of the 2(nd) and 4(th) harmonics. Refinement of the output structure is now being undertaken to ensure only the 4(th) harmonic signal is emitted