35 GHZ UPGRADE FOR PULSED ESR MICROSCOPE

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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 will construct and develop a pulsed ESR microscopy system (ESRM) designed for operation at 35GHz, which would improve upon our present 6-17GHz pulse ESRM. The upgraded system will be based on a separate microwave bridge of modular frequency design and pulse imaging probe, while the control computer, gradient current driver and magnet regulator systems will be shared with the existing 6-17GHz system. We expect the higher frequency system should enable the acquisition of 3D images of a variety of bio-samples with an improved resolution of ~2x2x5um (cf. present 3x3x8um) in a few minutes of acquisition. In order to extend the frequency coverage capability of our current pulsed ESRM, we will use a similar transceiver to that used in the existing system, with the addition of a frequency block converter. This implies the addition of a 9GHz to 35GHz frequency block converter between the transceiver and the microwave solid-state amplifier, and replacing the 6-18GHz microwave solid state amplifier by an appropriate 35GHz amplifier. At the end of this development, we will have two band-specific microwave bridges, operating at 6-18GHz and 35GHz. The microwave block converter and 1-10W 35GHz power amplifier are presently under development by the A. Blank research group at Technion Institute, Haifa, Israel, and will be made available to ACERT on a components-cost basis as part of a broader ESR microscopy collaborative development effort. In addition to the microwave bridge development work, we will further develop within ACERT the requisite fast gradient coil current pulse drivers. Our goal is to implement the capability to generate short rectangular gradients, where after a short rise time, the current in the gradient coil is maintained constant for the pulse sequence then rapidly reduced to zero, thereby limiting dissipation and maximizing the allowable repetition rate for frequency-encoded imaging.