High Power 200 GHz Pulsed/Continuous Wave (CW) Microwave Source for Dynamic Nuclear Polarization (DNP) Spectroscopy

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Our vision is to create a spectrometer for Nuclear Magnetic Resonance (NMR) that can detect signals that are hundreds of times weaker than can be achieved with even the very best conventional spectrometers. NMR methods are firmly established as a primary analytical tool in chemistry, are increasingly influential for characterisation in materials science and have revolutionised medical imaging. Despite the great success of NMR there remains a huge demand to push the boundaries by increasing the sensitivity and speed of the technique. This will enable NMR to be used in the study of a broad range of problems, including catalysis, batteries and fuel cells where today its impact is limited through lack of sensitivity. Furthermore, it is widely appreciated that structural information is key for understanding biological processes (e.g. protein folding, signal transduction etc.) and many problems will only be soluble if the sensitivity of NMR is dramatically increased. Dynamic Nuclear Polarisation (DNP) offers the exciting possibility to greatly increase the sensitivity of NMR by exploiting the inherently much larger polarisation of electron spins as compared to nuclear spins (e.g. ~ 2500 times for 13C). The DNP infrastructure at Warwick was funded by a £3.74M Basic Technology project (EP/D045967/1). All components of the DNP systems developed functioned at or above their design targets, except for the gyrotron microwave source which did not meet the necessary power/stability requirements for routine operation/exploitation. Nevertheless, large enhancements (60x) were achieved. The proposed new "turn-key" microwave source will provide significantly enhanced performance, is much more stable, agile, versatile and has significantly lower running costs than the gyrotron microwave source used to date. It will enable the continued rapid development and exploitation the DNP capabilities at Warwick. Development work will be done in collaboration with researchers at the Universities of Nottingham, St Andrews and Southampton while the enhanced DNP capabilities will be exploited by the wider vibrant UK MR community who will have access to a tool which enables research on systems previously out of reach. The research impact will be significant since the sensitivity enhancements in many applications are likely to be in excess of a few 100 times. The new capability will of course stimulate as yet unforeseen activities through the proposed pilot studies. The project objectives are: (a) Provision of a shared UK resource for CW DNP-enhanced solid-state NMR at a fraction of the cost of the current less able commercial system and with performance better than the current state of the art. (b) The development of pulsed DNP techniques with higher sensitivity than the current CW methodologies. This is possible because the new source can provide microwave pulses as well as continuous output and would be a unique capability. (c) DNP studies utilizing polarization sources with short electron relaxation times. This is possible because of the high power and versatility of the new microwave source and should greatly enhance the range of applicability of the enhancement technique.