The electron source is a critical component of the RUEDI (Relativistic Ultrafast Electron Diffraction & Imaging) facility, which needs to provide beam to match the re-quirements for performing both electron microscopy and ultrafast electron diffraction. To meet these demands, different operational modes are needed, to deliver ultra-short, ultra-bright and highly temporally and energy stable electron pulses with a charge varying from 0.2 pC to 20 pC and a kinetic energy of 4 MeV, with a repetition rate with 100 Hz (and higher). The dark charge produced by the electron source should be minimised to avoid significant noise in the image. Analysis of existing elec-tron sources suggested that the optimal solution is a normal-conducting S-band RF photocathode gun operat-ing with a metal photocathode, illuminated by an ultravi-olet laser. A number of critical design decisions were identified to reduce gun dark charge which are discussed in this paper. These include the gun RF design (number of cells and type of coupling), beam generation scheme (that includes the type of the photocathode), reducing duration of RF drive pulse and methods of maintaining good RF field stability.

RUEDI is a proposed relativistic ultrafast electron diffraction and imaging facility for the UK. It will deliver single-shot time-resolved imaging with MeV electrons, as well as ultrafast electron diffraction at 10 fs timescales. The few-MeV-scale imaging and microscopy line aims to deliver high charge (up to 10⁸ electrons), ultra-low emittance electron bunches to a 10µm sample with minimal energy spread and transverse divergence, aiming for imaging resolutions at the 10nm scale. The physical layout of the imaging beamline will be discussed, along with a multi-dimensional study of the beam dynamics of the proposed design. The extreme requirements on the injector specification, and the limitations inherent in such systems, will be investigated, and potential upgrade paths explored in terms of both imaging resolution and technological feasibility.

RUEDI (Relativistic Ultrafast Electron Diffraction & Imaging) is a proposed facility which will deliver single-shot, time-resolved, imaging with MeV electrons, and ultrafast electron diffraction down to 10 fs timescales. RUEDI is being designed to enable the following science themes: dynamics of chemical change; materials in ex-treme conditions; quantum materials; energy generation, storage, and conversion; and in vivo biosciences. RUEDI is proposed to be built at STFC’s Daresbury Laboratory in the UK. The Conceptual Design Review and Outline Instrument Design reports were published in November 2022 and summarised in this paper, with a Technical Design Review report to follow in November 2023.

RUEDI is a proposed relativistic ultrafast electron diffraction and imaging facility. It will have two beamlines: a diffraction beamline and an imaging beamline. This proceeding discusses the beam dynamics design of the diffraction beamline. The diffraction beamline needs to have the best temporal resolution possible which requires short bunch length and minimal time of arrival jitter at the sample. To achieve this a magnetic bunch compressor operated in a jitter cancelling configuration is used. To achieve compression as well as jitter cancellation the beam’s longitudinal space charge forces are used to modify the chirp to compress the beam. The RUEDI diffraction line will operate at 4 MeV meaning that both space charge forces and ballistic effects are significant and need to be accounted for in the design. The diffraction line will be operated in three modes: single-shot, stroboscopic and streaking.