250/500 GHZ GYROTRON BASED DNP/EPR SPECTROMETER

点击翻译按钮获取中文摘要

DESCRIPTION: This is an instrumentation proposal by Dr. Kreischer and colleagues (Drs. Temkin and Griffin at MIT) to develop a dynamic nuclear polarization (DNP) enhanced NMR spectrometer to operate at 254 GHz electron irradiation frequency (about 9 Tesla magnetic field and 380 MHz proton NMR frequency) and a 254 GHz electron paramagnetic resonance spectrometer. These instruments will share many components and assemblies in common. Later, there will be an effort to double the electron frequency to 508 GHz through harmonic generation in order to develop a truly high-field DNP-enhanced NMR spectrometer. The rationale for this DNP instrument is that 5T (140 GHz) DNP experiments in Professor Griffin's laboratory have demonstrated a 50-fold DNP enhancement of nitrogen-15 NMR signals from a nitrogen-15-labeled protein, T4 lysozyme, and that higher magnetic fields will give even stronger and better-resolved NMR signals from proteins, promising hitherto impossible NMR structure/function studies on biological macromolecules with molecular weights over 100,000. The new 9 Tesla DNP/NMR spectrometer to be developed is seen as an eventual replacement for the existing 5 Tesla system. The rationale for the 254 GHz EPR spectrometer is that 140 GHz EPR experiments in Professor Griffin's laboratory have demonstrated the practical advantages of exploiting the excellent Zeeman resolution afforded by high-field EPR to solve interesting and important biochemical problems and that in many cases, an extension to even higher fields will give even more information. The new 254 GHz EPR spectrometer is planned as a complement to, not a replacement for, the current 140 GHz spectrometer. To construct the DNP instrument, a new compact 100-watt source of 254 GHz millimeter-wave radiation must first be developed. The proposed EPR instrument will use a 5-inch-bore 9.4T NMR magnet with a 2T sweepable field and have a CW heterodyne reflection bridge with Gunn diode sources, quasi-optic circulator, corrugated waveguide, low-temperature Dewar, and cylindrical resonators. The proposed DNP/NMR spectrometer will incorporate a low-temperature magic-angle-spinning probe and transmit the millimeter-wave power to the sample through low-loss corrugated waveguide.