Abstract
Terahertz (THz)-based electron acceleration and manipulation has recently been shown to be feasible and to hold tremendous promise as a technology for the development of next-generation, compact electron sources. Previous work has concentrated on structures powered transversely by short, single-cycle THz pulses, with mm-scale, segmented interaction regions that are ideal for acceleration of electrons in the sub- to few-MeV range where electron velocities vary significantly. However, in order to extend this technology to the multi-MeV range, investigation of approaches supporting longer interaction lengths is needed. Here, we demonstrate first steps in electron acceleration and manipulation using dielectrically-lined waveguides powered by temporally long, narrowband, multi-cycle THz pulses that co-propagate with the electrons. This geometry offers centimeter-scale single-stage interaction lengths and offers the opportunity to further increase interaction lengths by cascading acceleration stages that recycle the THz energy and rephase the interaction. We prove the feasibility of THz-energy recycling for the first time by demonstrating acceleration, compression and focusing in two sequential Al2O3-based dielectric capillary stages powered by the same multi-cycle THz pulse. Since the multi-cycle energy achievable using laser-based sources is currently a limiting factor for the maximum electron acceleration, THz energy recycling provides a key enabling factor for reaching relativistic energies with existing sources.
Highlights
Femtosecond-duration relativistic electron beams are in demand for a wide range of applications from ultrafast electron diffraction [1,2] and microscopy [3] to ultrafast x-ray sources [4]
In the experimental setup (Fig. 1), a 53 keV phototriggered dc gun is used as an injector for the multistage dielectrically lined waveguides (DLWs)-based electron accelerator and manipulator which is powered by narrow-band, multicycle THz pulses
The electron beam from the DLW device is analyzed by a segmented terahertz electron accelerator and manipulator (STEAM) device [20], which is used as a streak camera to measure the bunch length with a resolution of approximately 150 fs, and by a tunable electromagnetic dipole coupled with a microchannel plate, which is used to measure the energy with a resolution of approximately 1 keV and deflection of the beam
Summary
Femtosecond-duration relativistic electron beams are in demand for a wide range of applications from ultrafast electron diffraction [1,2] and microscopy [3] to ultrafast x-ray sources [4]. Proof-ofprinciple demonstrations with single-cycle THz pulses have resulted in multi-keV acceleration [16,17] and high-field manipulations of electron-bunch phase space [18,19,20] proving the feasibility of compact THz-based devices for future radiation sources or as components for boosting the performance of existing accelerators as well as a promising solution to produce high-repetition, high-energy ultrafast electron bunches, which are highly desired in ultrafast electron diffraction [21,22]. Dielectrically lined waveguides (DLWs) have attracted interest in the accelerator community for their versatility to accelerate, manipulate, and characterize [25,26] electron beams They require a simpler fabrication process using commercial solutions with percent-level precision [27] which enable tuning of the phase and group velocity of the THz wave inside the DLW. Using only about 20 nJ of THz pulse energy, we accelerate 53 keV electrons by approximately 1.6 keV, which represents an approximately tenfold improvement in energy transfer between the THz and the electrons, compression of the electron bunch by a factor of 10 down to approximately 150 fs (FWHM), and spatial focusing the electron beam by a factor of 3
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