UK Light Source Review - Recommendations

Innovative Accelerator Research and Development

Recommendation 1 - The activity to develop an energy-recovery LINAC prototype (ERLP) at Daresbury should be encouraged as an innovative contribution to the international arena of accelerator science. We endorse the positive efforts to develop a center of excellence for accelerator science and technology at Daresbury. Modest proposals to expand the ERLP  facility to focus on accelerator developments, and possible extensions as a user facility should be pursued.

Proposed New Facilities

Recommendation 2 - The scientific activity behind the proposal to build the 4GLS facility has been productive and should be encouraged. There is a diverse user community engaged in the effort, and many innovative accelerator ideas in the design. In addition, it is clear that the UK community interested in the IR, VUV and soft-x-ray spectral regions is strong yet not well-satisfied by existing UK facilities. However, the committee feels that the 4GLS proposal, as it has been developed so far, is not convincingly the best step for the UK to provide the highest scientific impact to this community. The facility is technically ambitious - there are many capabilities embodied in one facility, from THz to soft x-rays. A key to the proposal is the simultaneous use of more than one color of light for pump and probe, yet it is not always clear, even to the potential users, how these might be used together. While the scientific case contains some really good ideas, it is not clearly matched to the facility plan. The committee believes that there is good science in this arena, but it needs to be more clearly articulated in the context of any proposed facility.

More significantly, the committee feels that possible role of “conventional” (i.e. non free-electron) lasers to provide better capabilities for several of the wavelength ranges in the 4GLS suite has not been sufficiently explored. When one considers the time scale and magnitude of the proposed investment for 4GLS, it seems that investments in laser developments could pay off handsomely. The Central Laser Facility (CLF) is a great resource for this sort of development, and with their experience in user facilities they could combine the appropriate amount of risk and predictability. One can anticipate, for instance, that the versatility of high-harmonic generation sources from gases and surfaces will improve substantially in the foreseeable future, especially with regard to average power, spectral range and tunability. In general, the portfolio of innovative laser-based sources is presently expanding with unprecedented vigor towards either side of the visible spectrum, opening new perspectives for user facilities. We recommend that the user community around the UK be brought together for one or more workshops on frontier science in the ultrafast and long wavelength regions, and this community be closely engaged in designing an innovative new proposal for a 4GLS which makes more extensive use of laser developments and has a more focused scientific case. Any developments should be evaluated in the European context, since there are several related VUV and soft x-ray facilities under construction or proposed in Europe. However, we expect that the UK could take a leadership role in Europe and beyond.

Recommendation 3 - The Diamond facility presented a proposal for Sapphire, an ultra-fast source for hard x-rays. This facility has been discussed with the Diamond scientific advisory committee, but has not yet had extensive discussion with the potential user community. The committee saw the possibilities in the proposed single pulse facility, which would provide short brilliant pulses but without lasing. However, the committee was concerned that the proposal, as shown, was simple but not highly innovative, and would likely be superseded by new laser-based technologies before it was finished construction. In addition the machine group at Diamond will be busy in the next few years making sure that the existing Diamond machine delivers on its promise during operations, with improved reliability and enhanced performance. The committee therefore felt that it is premature to go ahead with a formal proposal to build Sapphire in the next few years. Nevertheless, the committee encourages Diamond to involve its users in planning for the future of ultra-fast hard x-ray facilities in the UK and elsewhere, and to couple with the effort recommended above in the softer x-ray region.

Recommendation 4 - The involvement of the United Kingdom in the XFEL facility is very important for the future of x-ray science. Specific examples from the science presentations in the areas of atomic physics and high energy density physics showed that the UK has groups amongst the best in the world. It is suggested that a concerted effort be made to increase the science user community for XFEL through the funding of a research institute, like PULSE at Stanford, or the Center for Free Electron Laser Science at  DESY. The proposed Institute should encourage research at existing FEL facilities, at FLASH or the LCLS, in preparation for the opening of the XFEL. In general, the STFC can perform an important role as a portal to other facilities in Europe and worldwide, as they have done by supporting the ESRF and the XFEL. The role of the UK in developing detectors for XFEL is an important one, and should be broadened to include other FEL sources such as FLASH and LCLS. The CLF can play a similar role in the development of laser systems for these sources.

Existing Facilities and Proposed Upgrades

Recommendation 5 - The committee was impressed by the success to date of Diamond. A compelling story for the need of continued investment in Diamond beamlines was made. The facility did not yet have any major scientific results to show, but this is not unexpected considering that Diamond has not been running long. The committee is concerned that not all the beamlines at Diamond be “tied up” too soon. In particular, the committee felt that it is too early to commit to the construction of specific Phase III beamlines. The committee also recommends that the plans for construction of Phase II beamlines be opened for further discussion amongst the community as late as possible. It is also clear that a close cooperation with the Soleil source in France would be mutually beneficial, and could provide better support for the soft x-ray community in the UK. The committee was concerned about the apparent lack of instrumentation development at Diamond, and the perception that many beamlines have been purchased using “off-the-shelf” technology. The committee recommends that after Diamond has operated for three years, an independent international review committee be brought in to evaluate the success so far, and in particular the plans for the future, prior to firm plans for Phase III commitments.

Recommendation 6 - ESRF and its proposed Upgrade: The committee was impressed by the success of ESRF and the important role it plays for British scientists. It appears that the UK “gets its money’s worth” from ESRF, in that British scientists are very competitive with the community elsewhere in Europe. The proposed upgrade of ESRF will improve many beamlines for imaging and nanoscience, and the UK should provide support for this, while being intimately involved in ESRF user discussions on prioritization of upgrade projects.

Recommendation 7 - Central Laser Facility: It appears to the committee that the Central Laser Facility could play a larger role in the development of UK light sources. While they were coordinated to some extent in the proposals for 4GLS and Sapphire which were presented to the committee, it appears that the possibility of major developments in laser technology in concert with accelerator sources has not been fully considered. For example, the development costs aimed at the accelerator sources seem to be one to two orders of magnitude above those considered for new laser projects. The committee encourages the CLF to “think big” in its proposal for new light sources. One gets the impression that their ideas are tailored to fit into modest (one or two million pound) funding profiles, yet one can ask what they could do with ten times that number to revolutionize accelerator-based light sources which typically cost one hundred times more? In a European comparison CLF already has an unique record as "the" UK national facility in the laser sector, with an unusually large user community utilizing the breadth and high quality of the equipment and services being offered. Moreover, with their HiPER project CLF is pioneering the first truly international civilian laser project on a Giga-Euro scale. Hence, they are in a position, and should be strongly encouraged, to pursue plans for novel user-oriented light sources at a substantially larger funding profile than presently planned. Only then does a comparison between laser- and accelerator-based light sources appear meaningful.

We feel that with the strong user facility success of CLF, the opportunity exists for the UK to take a leadership role for laser-based light sources in the future. An essential step will be the identification of user needs through the workshops proposed in recommendation 2).

Recommendation 8 - Detectors: The committee applauds the UK involvement in detector development, with examples such as the new detectors planned for the XFEL, but recommends that the funding level for detector development be substantially increased. UK scientists should also expand their participation in international detector development projects.