Recent demonstrations of terahertz (THz) powered accelerators and beam manipulators have opened a pathway towards miniaturized accelerators that promise to enable new science due to unique features such as reduced timing-jitter and reduced space-charge broadening of the electron bunches. Here, we present on the development of a matchbox sized multi-layered accelerator structure powered by a single few-cycle terahertz pulse and designed to boost the output of a 55 keV DC electron gun to energies up to ~ 400 keV. An integrated actuated mirror is used to interfere the transversely injected THz pulse with itself, creating a transient standing wave optimized for efficient acceleration of the electrons. In contrast to a double-side-pumped approach this reduces the complexity of the optical setup by using the available THz energy more efficiently. We demonstrate first acceleration and map out the booster performance by varying the injection timing of the electrons and fine-tuning of the transient THz standing wave. Such a table-top source is promising for ultrafast electron diffraction experiments as well as precursor for subsequent acceleration to MeV energy by THz-driven LINACs.

Ultrafast electron diffraction (UED) is a powerful tool for the direct visualization of structural dynamic process-es in matter on atomic length and time scales. Observa-tions on a femtosecond time scale with atomic resolution spatially have long been a goal in science and are current-ly achieved with large photo injectors developed for FEL frontends. Here we demonstrate a compact 180 keV photocathode S-band electron gun, which employs field-enhancement at a pin-shaped cathode to produce an extraction field strength of 102 MV/m driven by a rack-mountable solid state 10 kW peak power supply. Simula-tions predict that high-brightness electron bunches with RMS duration of 10 fs, a radius of 135 μm, and spatial emittance of 0.1 mm-mrad are possible for a bunch charge of 10 fC. The impact of laser spot size and dura-tion, as well as their spatial distribution, on the temporal bunch length of electrons on the specimen was investigat-ed. Following the successful completion of the condition-ing phase of the RF gun and multipacting suppression, photo-triggered electrons using a UV laser on the photo-cathode were observed.