The Relativistic Ultra-fast Electron Diffraction and Imaging (RUEDI) project is an exciting project to develop an EPSRC funded facility for ultra-fast science on the Daresbury campus. The overall project lead is Prof Nigel Browning of the University of Liverpool and the other main project partner is the Rosalind Franklin Institute (RFI) at Harwell represented by Prof Angus Kirkland. The project is funded as a Preliminary activity under the UKRI Infrastructure Fund with the view to producing both Conceptual and Technical Design reports within the two-year grant period.
Our University and RFI partners have had a busy year developing the Science case for the RUEDI facility. Five science themes have been identified including 'Materials for Energy Generation, Conversion and Storage', 'Materials in Extreme Conditions', 'Bio-sciences' and Dynamics of Chemical Change' and 'Quantum Materials' along with a cross cutting 'Artificial Intelligence and Machine Learning' activity. A series of workshops were held across various sites in the UK focussing on the specific science themes. As a result of these meetings a community of interested academic partners has been identified and the RUEDI instrument requirements refined, particularly with respect to the array of laser and other pump sources needed to carry out the wide variety of experiments proposed.
ASTeC's main role in the project (with assistance from Liverpool and RFI) is the design of a suitable instrument to allow both ultra-fast diffraction (10-30 fs temporal resolution) and imaging (5-10 ps temporal resolution, 1-100 nm imaging resolution) to be achieved. Because of the very different electron beam requirements for Diffraction and Imaging, a design has evolved that has essentially two different beamlines each optimised for the particular application.
For Diffraction experiments, ultra-short electron pulses are required. There are a number of ways to achieve this, but the solution favoured involves the use of a magnetic bunch compression arc which can reduce the bunch length of the pulses produced by the electron gun whilst simultaneously supressing the time jitter of the beam. This technology choice has been successfully employed at a number of other facilities worldwide. The arc is followed by an interchangeable sample chamber that will allow a wide range sample types and environments to be achieved including liquid and gas samples and ultra-low temperature environments. The sample chamber is followed by electron optics to transport the diffracted electrons to a dedicated detector with single electron sensitivity. The line also includes diagnostics to measure the beam properties on a shot-by-shot basis.
On the Imaging line, there are optics to provide a small round beam at the sample and a radio frequency (RF) cavity used to reduce the energy spread of the beam; depending on the choice of lens technology this cavity may also be required to reduce the energy of the electron beam. Low energy spread, small spot size and short pulse length are all required at the sample making this line extremely challenging to design. The main lens of the imaging system also acts as the sample interaction point and several other lenses are also required to form the image of the sample on the detector downstream. As with the Diffraction line, there are significant diagnostics required to allow the beam to be characterised as part of the set-up procedure.
Along with the accelerator itself, the facility will also require a very large number of dedicated laser systems to allow the intended pump/probe experiments to be carried out. Firstly, a laser system will be needed to provide short ultra-violet pulses to the electron source which is an S-band RF photoinjector. In addition, there is a requirement to be able to deliver ultra-short pulses having a wide range of wavelengths directly to the samples. These pulses act as a pump to effect some physical or chemical change that can then be characterised in terms of the structure (diffraction) and composition and topography (imaging). By changing the delay between pump and probe these changes can be witnessed in real time to provide a deep understanding of the processes taking place. Because of the very wide range of science anticipated there are very varied requirements for the pump sources and hence the facility will provide extensive space for both the initially anticipated laser systems and future expansion.
The RUEDI project is an exciting opportunity for the UK to take a leadership role in the field of ultra-fast science, which is the new frontier in terms of understanding the key mechanisms that take place in chemical reactions and biological processes. These effectively define the real world performance of advanced materials and the mechanisms behind diseases and their potential treatments. The information produced by such a facility will have a significant effect in in generating the intellectual property that can enhance innovation activity UK wide. The Conceptual Design Report for the RUEDI facility was completed in November and submitted to EPSRC, who have since requested a bid to fund the facility construction to be considered for Wave 3 of the UKRI Infrastructure Fund. The Technical Design report will be completed by the end of the current project and a positive outcome to the funding bid is hoped for in due course.