MULTI CHANNEL TRANSMISSION LINE PROBES FOR HIGH FREQUENCY SOLID STATE NMR

如前几份报告所述，探测器的研制仍在继续 随着四谐振式输电的成功实施 500和750 MHz的线路探头。我们对此感到非常满意 在750 MHz的场强超过 在-100瓦时获得125千赫。进一步开发和应用 三重和四重共振实验需要高功率 目前正在测试的管状放大器。我们已经开发出 传输线MAS探头在以下方面有显著改进 几个重要领域的局部调谐探头：(1)效率，(2) 功率处理能力(电弧阈值和最大射频占空比)， (3)多声道可调谐性；(4)有效利用 磁体孔，以及(5)在大范围内不受干扰地运行 温度。两代设计已经在 频率从200兆赫到750兆赫。所有设计都基于 McKay等人提出的RF电路拓扑，其中唯一集总的 磁体内的调谐元件是(1)螺线管样品线圈和 (2)可选串联调谐电容器。低损耗空气介质 传输线用于以如下方式转换阻抗 允许以高效率和隔离度调谐多个频率。 每种情况下的一般拓扑都需要转换 与高频(H)电压节点一致的样品线圈电感 其中第一个物理结点位于磁体孔外。尖峰 该调谐电路内的电压被最小化(对于给定输入 功率)通过选择适当较低的电感值 调整和匹配。在低频方面，细节有所不同 视拓扑而定。在一种情况下，集总元件陷阱用于 隔离电路。在第二种情况下，低频节点是 用于电路隔离。为了达到高效率 在更高(&gt；500 MHz)频率下，我们开发了一种通用方法 这在高频时尤其有用。这些事态发展 已经允许设计和建造几个探测器，范围 从200 MHz到750 MHz，大多数都有三到四个高功率射频通道。 低温(&lt；150K)版本的此类探头使用射频工作 性能不会受到相对于 室温探头。

Probe development, as described in previous reports, has continued with the successful implementation of quadruple-resonance transmission line probes at 500 and 750 MHz. We have been extremely pleased with the efficiency of 'H operation at 750 MHz, with fields in excess of 125 kHz obtained with -100 Watts. Further development and application of triple and quadruple resonance experiments requires a high power tube amplifier that is currently being tested. We have developed transmission line MAS probes that offer significant improvements over locally tuned probes in several important areas: (1) efficiency, (2) power-handling capability (arc threshold and maximum rf duty cycle), (3) multi-channel tunability, (4) efficient use of space within the magnet bore, and (5) unperturbed operation over a large range of temperatures. Two generations of designs have been implemented at frequencies ranging from 200 to 750 MHz. All designs are based on the rf circuit topology proposed by McKay et al., where the only lumped tuning elements within the magnet are (1) the solenoid sample coil and (2) an optional series tuning capacitor. Low loss air-dielectric transmission line is used to transform impedance in a manner that allows tuning several frequencies with high efficiency and isolation. The general topology in every case requires transformation of the sample coil inductance to a high frequency (H) voltage node coincident with the first physical junction outside the magnet bore. Peak voltages within this tuning circuit are minimized (for a given input power) by choosing appropriately low values of inductance before tuning and matching. On the low-frequency side, details differ depending on topology. In one case, lumped element traps are used for isolation circuits. In the second case, low frequency nodes are exploited for circuit isolation. In order to achieve high efficiency at higher (>500 MHz) frequencies, we have developed a general approach that is particularly useful at high frequencies. These developments have permitted the design and construction of several probes ranging from 200 to 750 MHz, most with three or four high-power rf channels. Low-temperature (<150 K) versions of such probes operate with rf performance which is not significantly compromised relative to the room-temperature probes.