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

High-power, tunable source of coherent THz radiation driven by a microbunched electron beam

"Pre-bunched"or "microbunched"charged particle beams have attracted significant interest in the last decade. Potential applications of such beams include development of the next generation of THz and X-ray light sources. This work presents the conceptual design of a tunable source of coherent Smith-Purcell THz radiation based on plasma-assisted pre-modulation of the continuous beam, and conditioning of the micro-bunched beam. The numerical simulations were carried out from the beam modulation to THz radiation generation using a self-consistent numerical model as well as a semi-analytical approach. Such a source would be a possible and useful alternative to conventional vacuum THz tubes and THz FEL sources

Concept of a tunable source of coherent THz radiation driven by a plasma modulated electron beam

We have carried out numerical studies which consider the modulation of a picosecond long relativistic electron beam in a plasma channel and the generation of a micro-bunched train. The subsequent propagation of the micro-bunched beam in the vacuum area was also investigated. The same numerical model was then used to simulate the radiation arising from the interaction of the micro-bunched beam with a metallic grating. The dependence of the radiation spectrum on the parameters of the micro-bunched beam has been studied and the tunability of the radiation by the variation of the micro-bunch spacing has been demonstrated. The micro-bunch spacing can be changed easily by altering the plasma density without changing the beam energy or current. Using the results of these studies, we develop a conceptual design of a tunable source of coherent terahertz (THz) radiation driven by a plasma modulated beam. Such a source would be a potential and useful alternative to conventional vacuum THz tubes and THz free-electron laser sources

Novel grating designs for a single-shot Smith-Purcell bunch profile monitor

Smith-Purcell radiation has been successfully used to perform longitudinal profile measurements of electron bunches with sub-ps lengths. These measurements require radiation to be generated from a series of gratings to cover a sufficient frequency range for accurate profile reconstruction. In past systems the gratings were used sequentially and so several bunches were required to generate a single profile, but modern accelerators would benefit from such measurements being performed on a bunch by bunch basis. To do this the radiation from all three gratings would need to be measured simultaneously, increasing the mechanical complexity of the device as each grating would need to be positioned individually and at a different azimuthal angle around the electron beam. Investigations into gratings designed to displace the radiation azimuthally will be presented. Such gratings could provide an alternative to the rotated-grating approach, and would simplify the design of the single-shot monitor by reducing the number of motors required as all of the gratings could be positioned using a single mount

Experimental investigation of phase shifting in 1D Bragg structures for high power microwave pulse compression

The study of the quantum phase-space distribution of quarks and gluons inside nucleons in terms of TMDs and GPDs has become, in the last decade, a cutting-edge research field in hadron physics. These non-perturbative objects, respectively measurable in semi-inclusive deep-inelastic scattering and exclusive processes, allow to obtain 3-dimensional representations of the nucleon in the momentum and spatial coordinates as well as indirect insights into the still unknown parton orbital angular momentum. The HERMES experiment at HERA has been a precursor in this field. A selection of HERMES results sensitive to both TMDs and GPDs is presented

Novel grating designs for a single-shot Smith-Purcell bunch profile monitor

Smith-Purcell radiation has been successfully used to perform longitudinal profile measurements of electron bunches with sub-ps lengths. These measurements require radiation to be generated from a series of gratings to cover a sufficient frequency range for accurate profile reconstruction. In past systems the gratings were used sequentially and so several bunches were required to generate a single profile, but modern accelerators would benefit from such measurements being performed on a bunch by bunch basis. To do this the radiation from all three gratings would need to be measured simultaneously, increasing the mechanical complexity of the device as each grating would need to be positioned individually and at a different azimuthal angle around the electron beam. Investigations into gratings designed to displace the radiation azimuthally will be presented. Such gratings could provide an alternative to the rotated-grating approach, and would simplify the design of the single-shot monitor by reducing the number of motors required as all of the gratings could be positioned using a single mount