Wave propagation and tunneling through periodic structures

The phenomenon of tunneling manifests itself in nearly every field of physics. The ability to distinguish a wave tunneling through a barrier from one propagating is important for a number of applications. Here we explore the properties of the wave traveling through the band gap created by a lattice, either as a consequence of tunneling through the barrier or due to the presence of a pass band inside the gap. To observe the pass band for studying tunneling and propagating waves simultaneously, a localized lattice defect was introduced. The differences between the two phenomena are highlighted via waves' dispersion characteristics

GigaGauss solenoidal magnetic field inside bubbles excited in under-dense plasma

This paper proposes a novel and effective method for generating GigaGauss level, solenoidal quasi-static magnetic fields in under-dense plasma using screw-shaped high intensity laser pulses. This method produces large solenoidal fields that move with the driving laser pulse and are collinear with the accelerated electrons. This is in contrast with already known techniques which rely on interactions with over-dense or solid targets and generates radial or toroidal magnetic field localized at the stationary target. The solenoidal field is quasi-stationary in the reference frame of the laser pulse and can be used for guiding electron beams. It can also provide synchrotron radiation beam emittance cooling for laser-plasma accelerated electron and positron beams, opening up novel opportunities for designs of the light sources, free electron lasers, and high energy colliders based on laser plasma acceleration

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

Spectra of Coherent Smith-Purcell Radiation Observed from Short Electron Bunches: Numerical and Experimental Studies

MOPWA056 - ISBN978-3-95450-122-9International audienceThere is a significant interest in the development of compact particle accelerators within research areas including X-ray and THz (T-ray) sources of radiation, particle physics and medical sciences. To support the progress in these areas, non-invasive, electron beam diagnostics that are capable of measuring a single femtosecond electron bunch are required. At the current stage such beam diagnostics for femtosecond-long electron bunches are still not available. The goal of the work presented is to understand the spectral characteristics of coherent Smith-Purcell radiation to enable its quick and reliable interpretation including the longitudinal profile reconstruction of electron bunches. The research presented comprises results from numerical modelling and experimental studies. Using the numerical data, we discuss the radiated spectra dependence on the electron bunch profile and analyse the results. We also discuss the experimental data and compare it with theoretical predictions

Longitudinal Profile Monitor Using Smith-Purcell Radiation: Recent Results from the E-203 Collaboration

TUPC38 - Work supported by seed funding from the John Fell Fund, University of Oxford, Université Paris-Sud, program "Attractivité" and by the ANR under contract ANR-12-JS05-0003-01International audienceWe report on recent measurements made at FACET by the E-203 collaboration to test a longitudinal bunch profile monitor based on Coherent Smith-Purcell radiation. The capacity of this monitor to resolve sub-picosecond bunches will be shown as well as a comparison of profile reconstructed for different beam compression settings. We will also present recent electromagnetic simulations of the interactions between the beam and the grating as well as the expected resolution of such monitor. Comparison between Coherent Smith-Purcell radiation measurement and those made with other techniques will also be discussed. Finally future upgrades of the experiment and steps toward the construction of a single shot longitudinal profile monitor will be presented

Free-electron maser with two dimensional distributed feedback

Available from British Library Document Supply Centre-DSC:DXN045803 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Surface field excitation by an obliquely incident wave

Observation of surface field excitation by an obliquely incident wave inside a cylindrical two-dimensional periodic surface lattice is a step forward toward THz Cherenkov amplifiers. Here we observe and discuss this phenomenon, investigating it using different approaches. The results are compared, and it is shown that an increase in the lattice contrast results in excitation of surface fields by an obliquely incident wave resulting in the eigenmode formation. Measurements were conducted by studying forward transmission of the signal, and it is shown that the measured gaps in the spectra are associated with the eigenmode formation rather than band gap establishment

Experimental studies of the influence of distributed power losses on the transparency of two-dimensional surface photonic band-gap structures

Two-dimensional (2D) surface photonic band-gap (SPBG) structures have been suggested to realize 2D distributed feedback. The 2D SPBG structures can be obtained by providing 2D periodic perturbations of the waveguide surface. Such a structure can be used in a wide variety of applications including microwave electronics and integrated optics. The theoretically predicted effect of the transparency of the 2D SPBG structure when distributed Ohmic losses inside the structure are relatively high in comparison with the wave coupling coefficient has been observed in a series of experiments. The results obtained are in good agreement with theoretical predictions

Design of a high power W-band maser based on a two dimensional periodic structure

High power millimetre-wave sources operating in the W-band (75GHz-110GHz) frequency range are important for a number of applications. This work will focus on the design and construction of a high power maser operating in the W-band frequency range, which can be capable of generating spatially and temporally coherent radiation at a power of at least 10 MW

Wave interference and band gap control in multiconductor one-dimensional Bragg structures

A theoretical study of scattering and interference of waves in one-dimensional (1D) Bragg structures, also known as photonic band-gap (PBG) structures, based on multiconductor waveguides is presented. The case of small perturbations of the waveguide walls was analyzed. Using the coupled-wave theory the expression for the wave-coupling coefficient was generalized. The possibility of controlling the scattered wave polarization and the band gap locations in such structures due to the constructive and destructive interference of the waves was demonstrated. It was shown that such control can be achieved by adjusting the relative phase of the 1D periodic perturbations with respect to each other. As an example a 1D structure based on a coaxial waveguide was studied using three-dimensional computer simulations and coupled-wave theory. The dispersion diagrams are presented and the dependence of the reflected wave structure on the phase between the corrugations analyzed and discussed. To demonstrate the validity of the theory the results obtained for the basic coaxial model with a single corrugated conductor are compared with the experimental results observed