HYBRID PULSED FIELD GRADIENT COIL DRIVER

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。 为了进一步增强我们在脉冲ESR显微镜中的仪器能力，不同于C.W.，实验者可以直接测量许多关键参数，如自扩散、磁探针的弛豫时间、粘度、精确的O2浓度等，我们设计了一款性能先进的可编程脉冲梯度线圈驱动器。基于由我们现有的门控半正弦线圈励磁方案和快速开关恒流源组成的混合拓扑，新的梯度线圈驱动器设计既可以在可编程“矩形”模式下运行，以满足我们在脉冲序列期间对时间不变梯度的需求，也可以在以前的快速“正弦”梯度励磁模式下工作。快速脉冲矩形梯度的主要优点是它可以例如仅在每个成像脉冲序列期间打开，这使得操作员能够避免在频率编码的成像应用中的一个维度上产生恒定梯度的热的问题。 最终，随着进一步的发展，我们希望能够以0.5%的稳定性产生约100 ns的矩形短梯度脉冲。这种梯度可以在特定的微波脉冲期间选择性地开启，这将允许例如切片选择成像能力的可能性。此外，当工作在我们目前的半正弦电流驱动器模式下时，新的混合设计将能够提供更强和更短的脉冲场梯度，这是支持T2‘S在100-400 ns范围内对氮氧化物自由基的电子自旋共振M研究所必需的。在计划开发和改进梯度驱动器后，预计成像探头将能够产生持续时间约80 ns的半正弦脉冲场梯度。 设计并制作了一种双通道混合型脉冲梯度线圈驱动器样机，目前正在测试中。在来年，该装置将取代现有的仅半正弦线圈驱动器系统，并将在现场纳入和评估持续的开发升级。

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. To further enhance our instrumentation capability in pulsed ESR microscopy, where unlike c.w., the experimenter can directly measure many key parameters such as self diffusion, relaxation times of the magnetic probe, viscosity, accurate O2 concentration, etc., we have designed a programmable pulsed field gradient coil driver of advanced capability. Based on a hybrid topology consisting of our existing gated-haversine coil excitation scheme and a fast-switched constant-current source, the new gradient coil driver design can be operated in either a prgrammable "rectangular" mode to accommodate our need for time-invariant gradients during the pulse sequence, or the previous fast "haversine" gradient excitation mode. The main advantage of a fast pulsed rectangular gradient is that it can be turned on, for example, only during each imaging pulse sequence, which enables the operator to avoid the problem of a heat producing constant gradient in one of the dimensions for frequency-encoded imaging applications. Ultimately, with further development, we expect to be able to produce short rectangular gradient pulses of ca 100ns at 0.5% stability. Such gradients can be selectively turned on during a specific microwave pulse which would permit, e.g., the possibility for slice selection imaging capability. Furthermore, when operating in the mode of our present haversine current driver, the new hybrid design would be capable of stronger and shorter pulsed field gradients which are necessary to support ESRM studies of nitroxide radicals with T2's in the 100  400ns range. After the planned developments and improvements in the gradient drivers, it is anticipated that the imaging probes will be able to generate haversine pulsed field gradients with durations of ~80 ns. A two-channel prototype "hybrid" pulsed field gradient coil driver has been designed and constructed and is presently under test. During the coming year, this unit will replace the existing haversine-only coil driver system, and continuing developmental upgrades will be incorporated and evaluated in situ.