NEW PROBE HEADS FOR PULSE ESR EXPERIMENTS

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。我们常规使用17ghz低温探头，基于牛津CF935流动低温恒温器和耦合到ku波段波导的介电谐振器。该系统允许我们将温度降低到4.2 K或更低。在低温恒温器真空套内增加了一个涡轮分子泵站，以保持高真空，从而可以从一个60升液氦储存杜瓦瓶中连续获得样品在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微升的样品，并在最佳耦合下接受短至3.2 ns的脉冲。死区时间在39 ns以下，通过改进接收机保护器和改进谐振腔屏蔽，死区时间可以进一步提高。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微波工作室设计，并使用用于验证的内部微波工作台制造。利用CST Microwave studio，利用配备两个不同频率脉冲源的x波段光谱仪，对液氮温度下用于双电子-电子共振光谱（DEER）工作的腔型双峰谐振器进行了模拟。特别注意设计具有改善微波场磁分量均匀性的谐振器（B1）。这对于DQC工作和多脉冲序列的生成非常重要。虽然可以使用桥式环隙谐振器，但高功率脉冲可能导致拱。介质谐振器虽然具有高介电强度，但其场并不均匀。我们开发了一种类似于桥式环隙谐振器的均匀性改善的介电谐振器结构，并设计了介电谐振器的屏蔽和矩形波导耦合。

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.