  The ability to resolve the dynamics of matter on its native temporal and
spatial scales constitutes a key challenge and convergent theme across
chemistry, biology, and materials science. The last couple of decades have
witnessed ultrafast electron diffraction (UED) emerge as one of the forefront
techniques with the sensitivity to resolve atomic motions. Increasingly
sophisticated UED instruments are being developed that are aimed at increasing
the beam brightness in order to observe structural signatures, but so far they
have been limited to low average current beams. Here we present the technical
design and capabilities of the HiRES (High Repetition Rate Electron Scattering)
instrument, which blends relativistic electrons and high repetition rates to
achieve orders of magnitude improvement in average beam current compared to the
existing state-of-the-art UED instruments. The setup utilizes a novel electron
source to deliver femtosecond duration electron pulses at up to MHz repetition
rates for UED experiments. We provide example cases of diffraction measurements
on solid-state and gas-phase samples, including both micro- and nanodiffraction
modes, which showcase the potential of the instrument for novel UED
experiments.

Instrumentation and Detectors;Materials Science;Accelerator Physics