NEW PROBE HEADS FOR PULSE ESR EXPERIMENTS

点击翻译按钮获取中文摘要

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. We are using routinely a 17 GHz cryogenic probe-head, based on an Oxford CF935 flow cryostat and a dielectric resonator coupled to Ku-band waveguide. The system allows us to lower the temperature to 4.2 K or less. A turbomolecular pumping station was added to maintain a high vacuum inside the cryostat vacuum jacket making it possible to acquire DQC data continuously at 60-80 K at the sample for 120 hours from a single 60-liter liquid helium storage dewar. Samples can be changed in 2-3 minutes, which is important for studying multiple samples. The resonator accepts 2microL samples and accepts pulses as short as 3.2 ns at optimal coupling. Dead-time is under 39 ns and could be further improved after making modifications to the receiver protector and improving resonator shielding. Other probe-heads for this working frequency and for 9.5 GHz and 35 GHz are being designed using CST Microwave Studio from CST and fabricated with the in-house microwave workbench used for verification. Using CST Microwave studio, the simulations were done for a cavity-type bimodal resonator for double electron-electron resonance spectroscopy (DEER) to be used in work at liquid nitrogen temperatures with an X-band spectrometer equipped with separate pulse sources for two different frequencies. Special attention was paid to design the resonators with improved homogeneity of the magnetic component of the microwave field (B1). This is important for DQC work and for the generation of multi-pulse sequences. Although Bridged Loop Gap resonators could be used, high-power pulses may cause arching. Dielectric resonators while exhibiting high dielectric strength do not feature very homogeneous field. We developed a dielectric resonator (DR) structure with improved homogeneity similar to that of Bridged Loop Gap resonators and designed the DR shield and coupling to rectangular waveguide.