DEVELOPMENT OF A SOURCE OF A THz RADIATION BASED ON A 3-MeV ELECTRON BEAM AND FUTURE PLANS* A. V. Smirnov # , R. Agustsson, T. Campese, Y. Chen, J. Hartzell, A. Murokh, M. Ruelas, RadiaBeam Technologies Inc., Santa Monica, CA 90404, USA; W. J. Berg, J. Dooling, L. Erwin, R. Lindberg, S. Pasky, N. S. Sereno, Y. Sun and A. A. Zholents, Advanced Photon Source, Argonne National Laboratory, Argonne, IL-60439, United States; and Y. Kim, KAERI, 181 Mirae-ro, Geonchon-eup, 780-904, Daejeon, GyeongSangBuk-Do, South Korea. Abstract Design features and some past experimental results are presented for a sub-THz wave source employing the Advanced Photon Source's RF thermionic electron gun. The setup includes a compact alpha-magnet, four quadrupoles, a novel radiator, a THz transport line, and THz diagnostics. The radiator is composed of a dielectric- free, planar, over-sized structure with gratings. The gratings are integrated into a combined horn antenna and ~90° permanent bending magnet. The magnetic lattice enables operation in different modes, including conversion to a flat beam for efficient interaction with the radiating structure. The experiment described demonstrated the generation of narrow bandwidth THz radiation from a compact, laser and undulator-free, table- top system. This concept could be scaled to create a THz- sub-THz source capable of operating in long-pulse, multi- bunch, and CW modes. Additionally, the system can be used to remove unwanted time-dependent energy variations in longitudinally compressed electron bunches or for various time-dependent beam diagnostics. Plans for future experiments and upgrades are also discussed. INTRODUCTION For narrow bandwidth radiation generation, resonant Cherenkov radiation can be an attractive alternative to coherent undulator radiation. The radiation’s coherence is provided by the Cherenkov synchronism in the radiation producing device between the electron microbunch and fundamental eigenmode along the device’s interaction region of hundreds of radiation wavelengths. In the UCLA experiment [1], an 11 MeV electron beam from a laser-driven radio frequency (RF) photoinjector produced up to 10 µJ per RF macropulse at about mm wavelength, a fixed frequency radiation using a magnetic chicane for electron bunch compression and a 1-cm long quartz capillary tube. In the experiment presented here a thermionic electron RF gun generates a long train of momentum-chirped electron bunches which are compressed in an alpha- magnet. Coherent Vavilov–Cherenkov radiation is produced downstream of the magnet in a planar, partially open, slow-wave structure. It comprises a pair of electrically large, dielectric-free, high aspect ratio, metal gratings. To the best of our knowledge, an intense, tuneable, coherent radiation with a sub-mm wavelength was not produced to date using a completely laser-free and undulator-free table-top system with a few MeV electron beam. EXPERIMENTAL SETUP The experiment was jointly developed by RadiaBeam Technologies, LLC and the Accelerator Systems Division of Advanced Photon Source (APS) at Argonne National Laboratory (ANL) and conducted in the Injector Test Stand (ITS) of the APS. Figure 1 shows a schematic of the experimental setup. To obtain short electron bunches, low energy electrons are scrapped off inside the alpha- magnet vacuum chamber via a remotely controlled copper insertion aperture. Figure 1: Schematic layout of the experimental setup. Five beam steering correctors are not shown. The layout footprint is about (11.5) m 2 . A set of four quadrupole lenses is used to control vertical and horizontal beam envelops in the beamline to obtain a quasi-flat beam transverse profile in the THz radiator. The 2.5 cm short in-vacuum permanent magnet after the radiator directs the electron beam into a Faraday cup at the end of the beamline. The Cherenkov radiation exits to the air through a 3.7 cm diameter sapphire window and is transported to the interferometer by off- axis parabolic mirrors. The alpha-magnet has a maximum trajectory depth of 16 cm, minimum magnetic gap of 2.2 cm, and a maximum gradient of the magnetic field of 4 T/m. The alpha-magnet vacuum chamber includes a scraper to collimate low energy portion of the beam. The electron beam and beamline parameters are given in Table 1. The quadrupole gradients were pre-set using the values defined from beam transport simulations and ___________________________________________ #asmirnov@radiabeam.com TUPOW054 Proceedings of IPAC2016, Busan, Korea ISBN 978-3-95450-147-2 1892 Copyright © 2016 CC-BY-3.0 and by the respective authors 02 Photon Sources and Electron Accelerators A23 Other Linac-based Photon Sources