NEW PROBE HEADS FOR PULSE ESR EXPERIMENTS

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。我们通常使用17 GHz低温探头，它是基于牛津CF935流量低温恒温器和耦合到Ku波段波导的介质谐振器。该系统允许我们将温度降低到4.2K或更低。增加了涡轮分子泵站，以保持低温恒温器真空套内的高真空度，使从单个60升液氦存储杜瓦上连续获得60-80K下120小时的DQC数据成为可能。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。该谐振器可接受2微升样品，在最佳耦合条件下可接受短至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微波工作室进行设计，并使用内部微波工作台进行制造以进行验证。利用CST Microwave Studio，对用于液氮温度下的双电子-电子共振光谱(DER)的腔式双模谐振器进行了模拟，X波段光谱仪配备了两个不同频率的独立脉冲源。特别注意设计了具有改善微波场(B1)磁分量的均匀性的谐振器。这对于DQC工作和多脉冲序列的产生很重要。虽然可以使用桥式环路间隙谐振器，但高功率脉冲可能会导致拱形。介质谐振器虽然具有很高的介电强度，但场不是非常均匀。我们提出了一种类似于桥接环隙谐振器的介质谐振器结构，并设计了介质谐振器的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.