DEVELOP A 250 GHZ GYROTRON FOR DYNAMIC NUCLEAR POLARIZATION & NMR SPECTROSCOPY

点击翻译按钮获取中文摘要

The main goal of this research program is to design and construct a gyrotron-based spectrometer suitable for dynamic nuclear polarization/nuclear magnetic resonance (DNP/NMR) and electron paramagnetic resonance (EPR) at 250 and 500 GHz. The motivation for this effort is the recent success at MIT with similar instrumentation at 140 GHz. We anticipate similar improvements with the systems that are presently being built for our studies at higher frequencies. Three research projects are underway: (1) construct a compact, 250 GHz cw gyrotron capable of producing 100 watts of rf power, (2) assemble a 375 MHz NMR system in order to perform DNP experiments using the gyrotron, and (3) modify the gyrotron to generate second harmonic power at 500 GHz. We also proposed investigating the possibility of operating the tube as an amplifier or as a tunable source. We have focused our attention over the past year on designing and constructing the 250 GHz gyrotron system, and buying the components needed for the EPR spectrometer. The planned DNP/EPR experiments at 250 GHz offer the potential for significant signal enhancement and improved resolution. These experiments require a source with a cw output power of at least 100 W. At the present time, there are very few sources of radiation at millimeter and submillimeter wavelengths capable of such high powers. In the past, most DNP/EPR experiments conducted above 40 GHz relied on slow wave devices to generate the necessary rf power. Such devices require an electron beam to pass by a slow wave structure in order to generate the microwave radiation. As the frequency increases, the physical size of these structures decreases, resulting in higher power densities that can have a detrimental effect on the circuit reliability. These factors ultimately limit the output power and lifetime of slow wave devices at the frequencies of interest for these experiments. The gyrotron utilizes a robust fast-wave circuit, and offers a viable solution to these problems.