论文标题
LCLS-II的相位参考线的安装，调试和性能
Installation, Commissioning and Performance of Phase Reference Line for LCLS-II
论文作者
论文摘要
分布式系统的任何腔控制器都需要一个相位参考线（PRL）信号，以从中定义腔场测量的阶段。 SLAC的LCLS-II PRL系统在1300 MHz的双向（正向和反向）相位引用到LLRF系统的每个机架。带有主振荡器（MO）嵌入的PRL控制器将两个方向的平均相锁定到MO本身。固件中应用了相平均跟踪循环，该固件支持取消由PRL电缆长度变化引起的相位漂移的功能。 FPGA逻辑移动数字LO的阶段，以获得两个PRL信号的零平均相。同样的LO用于处理腔拾取信号，从而建立了一个用于关键腔RF测量值的稳定参考阶段。在低频率下，相对于LO分布的开环PRL噪声包括强烈的环境和1/F组件，但是闭环噪声接近DSP的噪声底。这意味着，腔的近相噪声将由机箱DAQ噪声主导。与机器操作相关的最终循环相位噪声是相对于光束的空腔场的噪声。
Any cavity controller for a distributed system needs a Phase Reference Line (PRL) signal from which to define phases of a cavity field measurement. The LCLS-II PRL system at SLAC provides bidirectional (forward and reverse) phase references at 1300 MHz to each rack of the LLRF system. The PRL controller embedded with the Master Oscillator (MO) locks the average phase of the two directions to the MO itself. Phase-averaging tracking loop is applied in firmware which supports the feature of cancelling the phase drift caused by changes in PRL cable length. FPGA logic moves the phase of digital LO to get zero average phase of the two PRL signals. This same LO is used for processing cavity pickup signals, thus establishing a stable reference phase for critical cavity RF measurements. At low frequencies, open-loop PRL noise relative to the LO distribution includes a strong environment and 1/f components, but the closed-loop noise approaches the noise floor of the DSP. The implication is that the close-in phase noise of the cavities will be dominated by the chassis DAQ noise. The final out-of-loop phase noise relevant to machine operations is that of the cavity field relative to the beam.
