95 GHZ PULSE SPECTROMETER DEADTIME REDUCTION

95 GHZ 脉冲光谱仪死区时间缩短

• 批准号: 7723968
• 负责人: CURT R DUNNAM
• 金额: $ 0.26万
• 依托单位: CORNELL UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-01 至 2009-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7723968
• 关键词: Adverse effects; Agreement; Amplifiers; Biological; Companions; Computer Retrieval of Information on Scientific Projects Database; Data; Evaluation; Floor; Funding; Grant; Institution; Length; Logic; Modification; Noise; Physiologic pulse; Pulse taking; Research; Research Personnel; Resolution; Resources; Sampling; Schedule; Solutions; Source; System; Time; United States National Institutes of Health; cryogenics; design; falls; nanosecond; present value; programs

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. Deadtime in the ACERT 95 GHz pulse spectrometer is presently around 40 nanoseconds, which carries substantial impact on the system SNR, and therefore spin sensitivity. This limitation is significant when collecting data on biological samples of low concentration. Our estimate is that the spectrometer's present intrinsic deadtime can be reduced to 15 ns or less by a.) modifications to the Extended-Interaction klystron Amplifier (EIA) modulator and b.) reduction of the quasioptical bridge corrugated waveguide length. With regard to the latter contribution we note that the ringdown time of the present 900mm corrugated waveguide section is predicted to be ca 20ns, a figure that is in good agreement with our low power evaluation data. Installation of the Cryogenic, Ltd. 9T magnet to replace the present Oxford 6T magnet, scheduled for late August, will permit substituting a 300mm section for the present corrugated waveguide section, thereby reducing the waveguide length and ringdown time by a factor of 3. The resulting waveguide-related deadtime contribution in attaining the spectrometer receiver noise floor of approximately 1 nW from an initial level of 1KW will accordingly fall from 20ns to 6.7ns. Regarding the modulator timing, the modulator internal timing hardware was initially designed to operate for a fixed retriggerable interval of approximately 1 ¿s to simplify the original external timing system configuration consisting of discrete timing modules. This "triggerable" hardware option, however, has the unwanted side effect of introducing around 10ns r.m.s. modulator turn-off jitter, which contributes about 20ns of additional deadtime. The solution to this minimizing this deadtime contribution is straightforward. Our 95 GHz spectrometer timing system has been upgraded with a commercial multichannel programmable card and companion high-resolution (1ns) card of ACERT design. A suitably programmed timing control line, with our planned modulator internal logic modifications, will permit us to operate the EIA modulator in a "strobed" mode, where the modulator turn-off time will then reflect the system's intrinsic resolution of 1ns and a deadtime improvement of about 20ns. We estimate that the two system improvements described in this Subproject will reduce the 95 GHz deadtime to ca 15ns, from the present value of ca 40ns.

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 ACERT 95 GHz脉冲光谱仪中的死区时间目前约为40纳秒，这对系统SNR产生了重大影响，因此对自旋灵敏度产生了重大影响。在收集低浓度生物样品的数据时，这一局限性很大。我们的估计是，光谱仪的本征死区时间可以减少到15 ns或更少的a。对扩展互作用速调管放大器（EIA）调制器的修改和B.）减少准光桥波纹波导长度。关于后者的贡献，我们注意到，目前的900毫米波纹波导部分的衰荡时间预测为约20纳秒，这是在良好的协议与我们的低功率评估数据的数字。计划于8月下旬安装Cryogenic有限公司的9T磁体以取代现有的Oxford 6T磁体，这将允许用300mm的部分取代现有的波纹波导部分，从而将波导长度和振铃时间减少3倍。因此，在从1KW的初始水平获得大约1nW的光谱仪接收器噪声本底时，所得到的波导相关死区贡献将从20ns下降到6.7ns。关于调制器定时，调制器内部定时硬件最初设计为在约1 μ s的固定可重新触发间隔内运行，以简化由离散定时模块组成的原始外部定时系统配置。然而，这种"可重构"的硬件选项具有引入约10ns r.m.s.的不希望的副作用。调制器关断抖动，其贡献约20ns的额外死区时间。最小化这种死区贡献的解决方案很简单。我们的95 GHz频谱仪定时系统已升级为商用多通道可编程卡和ACERT设计的配套高分辨率（1 ns）卡。适当编程的时序控制线，以及我们计划的调制器内部逻辑修改，将允许我们在"选通"模式下操作EIA调制器，其中调制器关断时间将反映系统的1ns固有分辨率和约20ns的死区时间改善。我们估计，在这个子项目中描述的两个系统改进将减少95 GHz的死区时间约15纳秒，从目前的值约40纳秒。