NEW PROBE HEADS FOR PULSE ESR EXPERIMENTS

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。我们经常使用17 GHz的低温探头，头的基础上，牛津CF 935流量低温恒温器和介质谐振器耦合到Ku波段波导。该系统使我们能够将温度降低到4.2 K或更低。增加了一个分子泵站，以保持低温恒温器真空夹套内的高真空，使其能够从单个60升液氦存储杜瓦瓶中连续获取样品在60-80 K下120小时的DQC数据。样品可以在2-3分钟内更换，这对于研究多个样品非常重要。谐振器接受2 microL的样品，并在最佳耦合时接受短至3.2 ns的脉冲。死区时间小于39 ns，在对接收器保护器进行修改和改进谐振器屏蔽后，死区时间可以进一步改善。该工作频率以及9.5 GHz和35 GHz的其他探头正在使用CST的CST Microwave Studio进行设计，并使用用于验证的内部微波工作台进行制造。利用CST微波工作室，对液氮温度下双电子-电子共振谱（DEER）腔型双模谐振器进行了模拟，并在X波段谱仪上配备了两个不同频率的独立脉冲源。特别注意的是，设计的谐振器的微波场（B1）的磁分量的均匀性得到改善。这对于DQC工作和多脉冲序列的产生是重要的。虽然可以使用桥接环隙谐振器，但高功率脉冲可能导致振荡。介电谐振器虽然表现出高介电强度，但其场并不非常均匀。提出了一种介质谐振器（DR）结构，它具有类似于桥接环隙谐振器的均匀性，并设计了DR屏蔽和与矩形波导的耦合。

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.