A Compact, High-power Terahertz Amplifier for DNP-NMR and EPR Spectroscopy

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DESCRIPTION (provided by applicant): We propose to develop a compact, cost-effective Traveling Wave Tube (TWT) amplifier at 263 GHz with 50 W of peak power, 5 W of continuous wave power and 5% instantaneous bandwidth for application in Dynamic Nuclear Polarization (DNP) enhanced solid-state and solution-state NMR and Electron Paramagnetic Resonance (EPR) spectroscopy. With DNP, the inherently small signal intensities in a NMR experiment can be enhanced by up to two orders of magnitude. This significantly increased overall sensitivity will be highly beneficial for analytical applications of NMR spectroscopy as well as in the structure determination of bio- macromolecules using NMR methods. Currently, DNP is performed with either low power solid-state sources (whose output power is limited to a few mW at frequencies >300 GHz) and at low temperatures in the range of 20-30 K (to compensate for low microwave power) or with large, gyrotron systems which can generate 50 W of power. Gyrotrons are expensive and do not possess sufficient tuning bandwidth (<0.1%) necessary for investigating a wide range of DNP experiments and thus require expensive sweep coils in the NMR magnets. The proposed TWT will address all the above concerns. The TWT can also be used as an external amplifier on a commercial 263 GHz EPR spectrometer to significantly improve the output power capability by 30dB. The TWT is expected to cost less than one-fourth of the cost of a gyrotron system, provide 5% instantaneous bandwidth and will be a compact table-top system. These advantages will allow a larger number of researchers to take advantage of the sensitivity boost offered by DNP in NMR experiments. In Phase I, we will design, build and test key subsystems of the of the TWT including the electron gun, the compact permanent magnet system and the interaction structure. The latter will be built on a state-of-the-art nano-computer numerical controlled (CNC) milling machine to achieve the high precision and surface quality necessary for operation at such high frequencies. The successful testing of the key subsystems will enable optimization of the design for a full prototype in Phase II. The technology is scalable and can be used at frequencies as high as 593 GHz (900 MHz NMR). A higher peak power version of the device will advance the state-of-the-art in high field EPR spectroscopy. As an ultimate result of this project, we expect Bridge12 to offer commercial TWTs from 263 GHz(400 MHz NMR) to 593 GHz (900 MHz NMR) for DNP-NMR and EPR spectroscopy. This will greatly accelerate structure determination of bio-macromolecules of relevance to human disease research funded by NIH.