Automatic phase calibration for RF cavities using beam-loading signals
Precise calibration of the cavity phase signals is necessary for the operation of any particle accelerator. For many systems this requires human in the loop adjustments based on measurements of the beam parameters downstream. Some recent work has developed a scheme for the calibration of the cavity phase using beam measurements and beam-loading however this scheme is still a multi-step process that requires heavy automation or human in the loop. In this paper we analyze a new scheme that uses only RF signals reacting to beam-loading to calculate the phase of the beam relative to the cavity. This technique could be used in slow control loops to provide real-time adjustment of the cavity phase calibration without human intervention thereby increasing the stability and reliability of the accelerator.
Beam-based phase monitoring and gradient calibration of Jefferson Laboratory RF systems
Beam-based monitoring was instituted at Jefferson Lab in December of 1994 to correct the RF system phase setpoints against drifts of the master oscillator system, while running transparently to normal beam setup and delivery operations. As then implemented, the master oscillator distribution was subject to large thermal drifts, but no means existed of tracking the distribution of drifts, nor of identifying phase errors for individual cavities following maintenance activities. The background process implemented is capable of cresting each of the 312 cavities in the linacs to within approximately /spl plusmn/2 degrees. In addition, during dedicated system measurement operations, the RF cavity gradients have been calibrated with beam to within a tolerance of approximately /spl plusmn/5%. These beam-based results are in many cases more than 20% different from commissioning results using RF measurement techniques.
High-speed data processing module for LLRF
The linear accelerators, like Free-electron LAser in Hamburg (FLASH) or the European X-Ray Free Electron Laser (E-XFEL) take advantage of digital Low Level Radio Frequency (LLRF) system to control the phase and amplitude of electromagnetic field inside superconducting cavities. The real-time control LLRF system, processing data within a few micro seconds, must fulfil the performance requirements and provide monitoring and diagnostics. The AMC-based Controller (DAMC-TCK7) board was developed as a general purpose high-performance low-latency data processing unit designed according to the PICMG MTCA.4 spec. The module provides processing power, data memory, communication links, reference clock, trigger and interlock signals that are required in modern LLRF control systems. The module was originally designed as a Low Level Radio Frequency cavity field stabilizing controller for standing-wave linear accelerators. However, the application of the board is much wider, it is general purpose data processing module suitable for systems requiring low latency and high speed digital signal processing. This paper discusses the requirements for the digital real-time data processing module and presents the laboratory performance evaluation.