研究目的
Investigating an alternative and novel means of beam phase determination based on beam-excited higher order electromagnetic modes and the accelerating electromagnetic mode in superconducting radio frequency cavities.
研究成果
The monitor presented in this paper is the first type that can directly and online monitor the phase between the electron beam and the RF field inside a cavity. This will provide valuable diagnostic information for the LLRF system, such as the long-term monitoring of the stability of the beam phase. The electronics for the European XFEL are under development.
研究不足
The resolution of the beam phase determination depends critically on the signal to noise ratio. The discrepancy between the obtained resolution and the theoretical limit is due partially to the RF components used during the measurements.
1：Experimental Design and Method Selection:
A coupled resonant circuit model was developed to study the dynamics of the second monopole band. The circuit model was implemented in Simulink and solved with a 5 ps step.
2：Sample Selection and Data Sources:
Measurements were made at the European X-ray Free Electron Laser (XFEL) injector module using a fast oscilloscope.
3：List of Experimental Equipment and Materials:
The experimental setup consists of several RF band-pass filters, a combiner/splitter, and a fast Tektronix scope TDS6604B (20 GS/s with 6 GHz bandwidth).
4：Experimental Procedures and Operational Workflow:
The signal from each HOM coupler was transmitted by a RF cable with a length of approximately 60 m from the tunnel to the measurement rack. The signal was then split with a Mini-Circuit power splitter. Each split signal was filtered, one centered at approximately 1300 MHz with 100 MHz bandwidth and the other at approximately 2435 MHz with 190 MHz bandwidth. The filtered signals were then combined again before they were fed into the fast scope.
5：Data Analysis Methods:
The phase of the 1.3 GHz signal was varied to simulate a RF phase change and then retrieved based on the procedure described in the Appendix. The calculation was performed independently for HOM1 and HOM2. The RMS of the phase difference between HOM1 and HOM2 was used to evaluate the resolution of the beam phase determination.
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