95 GHZ PULSE SPECTROMETER DEADTIME REDUCTION

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 ACERT 95 GHz脉冲光谱仪中的死时间目前约为40纳秒，这对系统信噪比和自旋灵敏度有很大影响。在收集低浓度生物样本的数据时，这一限制是显著的。我们的估计是，光谱仪目前的固有死区时间可以减少到15 ns或更少。对扩展互作用速调管放大器(EIA)调制器和b.准光桥波纹波导长度的缩短。关于后者的贡献，我们注意到目前900 mm波纹波导段的振铃时间被预测为约20 ns，这一数字与我们的低功率评估数据很好地吻合。计划于8月下旬安装的低温9T磁体将取代目前的牛津6T磁体，这将允许用300 mm的部分替代目前的波纹波导部分，从而将波导长度和振铃时间缩短3倍。由此产生的与波导相关的死区时间贡献将从最初的1KW降至约1NW，从而使光谱仪接收器噪声下限从20纳秒降至6.7纳秒。关于调制器时序，调制器内部时序硬件最初设计为在大约1？S的固定可再触发间隔内工作，以简化最初由离散时序模块组成的外部时序系统配置。然而，这种“可触发”的硬件选项有一个不受欢迎的副作用，即引入大约10 ns的RmS。调制器关断抖动，这造成了大约20 ns的额外死区时间。解决这一问题的方法很简单，可以最大限度地减少这种死区贡献。我们的95 GHz光谱仪计时系统已经升级，配备了商用多通道可编程卡和Acert设计的配套高分辨率(1 Ns)卡。经过适当编程的时序控制线，加上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，在该模式下，调制器关断时间将反映系统固有的1 ns分辨率和大约20 ns的死区时间改进。我们估计，本子项目中描述的两项系统改进将把95 GHz死区时间从目前的40 ns减少到15 ns。

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.