CRYOGENIC BORE UPGRADE FOR 6T MAGNET

Cornell University, Ithaca NY

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. ACERT currently possesses an Oxford 6T magnet that has been in use with our 95GHz cw/pulse spectrometer since completion of the initial instrument configuration in 2002. This magnet exhibits good homogeneity and low cryogen consumption but, as supplied, has two major drawbacks[unreadable]a relatively narrow 50mm bore and limited allowable insert temperature range of approximately -10[unreadable] C to +60[unreadable] C. The narrow bore precludes the use of a vacuum dewar for ESR spectroscopy, with the unprotected bore temperature range limitation due to its copper insert wall and neoprene "o"-ring end seals. This type of seal hardens and contracts at temperatures below approximately -30[unreadable] C, effects which inevitably cause vacuum leakage and quench of the magnet. Our desire, having upgraded the 95GHz spectrometer experimental control capabilities for new experiments such as DEER 3- and 4-pulse and DQC distance measurements is to run these experiments at cryogenic temperatures. Although we are currently preparing a new cryogen-free 9T magnet (Cryogenic, Ltd.) for use with the spectrometer, during the initial phase of testing and fine-tuning the instrument experimental capabilities we prefer to expedite development and avoid introducing anomalies by continuing with the Oxford 6T magnet setup. Therefore, we designed and constructed a cryogenic-capable Controlled Temperature Insert (ref. Subproject 0162) for the Oxford magnet and rebuilt the magnet with custom cryo-rated internal dewar end seals (Creavey Seal Co.) and stainless-steel bore pipe to withstand bore temperatures down to at least 77K. Following this rebuild effort, we have operated the CTI at sample and bore pipe temperatures down to 80K without incurring any magnet vacuum problems.