CONSTRUCTION OF NEW 170 & 250GHZ CW- ESR SPECTROMETER

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We have built our new HFHF-ESR cw spectrometer with improved, low-loss, broadband quasioptical components and incorporated it into the new 9T magnet purchased from Magnex. The observed improvements in signal to noise accruing from these upgrades, due in large part to the reduced insertion loss of the quasioptical bridge and higher mechanical stability of the new setup, are crucially important for the wide variety of biological samples in aqueous media that we study. The flexibility of the newly configured bridge is also important for the development work on circular dichroism ESR (CD-ESR) that we are undertaking. The upgrades that we are implementing will also improve the performance of our goniometer for single crystal rotation studies, because of the reduced cross-sectional area of the quasioptics in the wam bore of the new magnet. The increased accessible bore cross-sectional area allows a more robust mechanical control mechanism as well as a more efficient cryogenic control system which we have recently tested. The major improvement to the bridge implemented this year has been the installation of more powerful and reliable millimeter wave sources based on advances in the state-of-the-art for high-frequency multipliers. We have been able to increase the available power at 170GHz by a factor of 4 compared to our old source. At 240GHz we have achieved an improvement by an order of magnitude in the available power compared to our old source. In addition, the power level is conveniently controllable by the operator, as is the frequency. Furthermore, modifications to the source for implementation of CD-ESR or other advanced concepts will be much easier to affect as there is no phase-locked loop at the millimeter wave frequency. Such a phase-lock loop was an integral part of our old sources which made modification and servicing very difficult.