Report on AGTAX 2015 Workshop

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Dr. Ralph Fiorito, Sr. Marie Curie Fellow and Quasar group member, attended the fifth workshop on Accelerator Generated Tera-Hertz and X-rays hosted by the Physics Department of Oxford University on March 18-19, 2015. The focus of this workshop was presentation of results of current research on intense THz and x-radiation generation from accelerated charge particle beams interacting with materials, structures and lasers. This is a rapidly growing field with important applications to non-destructive testing, security screening, medical therapy and accelerator diagnostics. The workshop attracted leading international experts and researchers and covered a wide range of efforts in simulation, theory and experiment. The group was small enough (~40) and the talks few enough to allow a great deal of discussion during the meeting.
The first day started off with a talk by A. Ponomarenko of MEPhI who presented theoretical and simulation work on THz generation from an electron beam passing through a corrugated dielectric cylinder. However, the theoretical assumptions and analysis presented were far from realistic and the comparisons between theoretical calculations and simulations (CST) were rather poor. On the other hand the talks that followed: x-ray generation via Cherenkov radiation produced from materials and structures, where the index of refraction is anomalous, by A. Tishchenko; advances in room temperature Schottky diodes, highly sensitive THz detectors that can be miniaturized to produce a 2D imaging array presented by P. Huggard of RAL; and coherent THz radiation generated by bunches in an electron storage ring by M. Schwartz of KIR were exceptionally clear and thorough.  To conclude the first day’s sessions, A. Seryi, Head of the John Adams Institute, gave an entertaining, popular lecture on the art of scientific inventiveness describing how techniques borrowed from industrial brainstorming and associated scientific efforts in other fields can be applied to solve physics problems effectively.  
A. Aryshev from KEK, started off the second day with a talk on pre-bunching electron beams to shorten the radiation gain or growth length of coherent radiation produced in a free electron laser. I. Konoplev, from Oxford presented his group’s work on the development of Smith Purcell (SP) sources (electron beams interacting with periodic structures e.g. gratings) to produce THz radiation. However, both of these talks failed to mention significant previously work done by other researchers.  Consequently, both the context and novelty of their contributions were obscured.
More interesting and enlightening results were presented by R. Seviour, U. of Huddersfield, who gave an excellent talk about the interaction of electron beams with effective media (artificial electromagnetically active structures) to enhance the generation of THz radiation; A. Murokh, Radiabeam Technologies, who presented his company’s efforts to produce commercially viable THz and x-ray Compton sources using compact accelerators; and B. Hidding from U. Strathclyde who presented a comprehensive talk on the production of x-rays via Compton scattering from electron beams produced by laser induced plasma wake-fields.
R. Fiorito’s presentation: “Novel electron bunch length diagnostic using the angular distribution of coherent THz diffraction radiation”, initiated a series of presentations on the applications of THz radiation for beam diagnostics. This talk stimulated some lively discussions because of the novelty and simplicity of its approach, i.e. the use of the angular distribution rather than the spectrum of THz radiation, which is the basis of many bunch length measurement methods.
Following this,  A. Fisher (SLAC) presented his results on THz diagnostics and generation of THz from the ultashort, i.e. tens of femtoseconds (10-15 sec) bunches produced by SLAC’s LCLS and FACET accelerators; D. Walsh from Daresbury (ASTEC) explained a new technique to measure the time profile of an ultra-short electron bunch by upshifting the THz field that is induced in an electro-optic crystal by a passing bunch of electrons, to the optical regime where it can more easily be detected; and F. Thaeri of Oxford presented an advanced phase constrained algorithm to retrieve bunch lengths from spectrally based diagnostics.
Two interesting tutorial talks one by R. Bingham from RAL on the present status of plasma wakefield accelerators and the other by A. Seryi on the prospect for applications of laser wakefield X and THz sources concluded the workshop.

Slides of the presentations are presently unavailable. However, the conference leaders have promised pending approval of the authors that most of the talks will be uploaded to the conference website in the near future.