Design and Test of a Klystron Intra-Pulse Phase Feedback System for Electron Linear Accelerators

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In view of the fact that beam stability and timing jitter are of great interest and of increasing importance in the field of modern linear accelerators, the present work on the development and testing of a klystron phase feedback system within a pulse could be of importance in this field and represents an original approach. I recommend that this work be published if it contains some clarifications and improvements:

1) All acronyms (standard acronyms and author-defined acronyms) should be defined at first mention in the abstract and in the body of the article. Authors should define abbreviations and acronyms when they are used for the first time in the text, even if they have already been defined in the abstract. Abbreviations such as RF, LNF, SPARC_LAB and PFN are not defined in the abstract, but should be. Abbreviations such as HV, LO and some others are not defined in the text.

2) The customized oven-controlled crystal oscillator with low phase noise is used as the reference master oscillator in the system. The authors should specify the phase noise value of this reference master oscillator. In addition, it would be useful for the readers of this paper if the authors would cite some papers previously published in this journal that deal with the measurement of phase noise of oscillators, such as:

Lavrič, A.; Batagelj, B.; Vidmar, M. Calibration of an RF/Microwave Phase Noise Meter with a Photonic Delay Line. Photonics 2022, 9, 533. https://doi.org/10.3390/photonics9080533

3) In addition, the authors mention numerous experiments on conventional SASE and seeded FELs, Thomson backscattering, THz generation, plasma beam focusing and acceleration (PWFA) with FEL generation and laser interaction with matter, but they make no reference to these experiments.

4) The authors mention the Libera LLRF system in the paper. Again, it would be very helpful to the reader if the authors gave a reference to this system. The authors should add a reference to a publication about the Libera LLRF system.

5) Authors should describe the acronyms shown in Figure 2 in the caption of this figure.

6) The authors should explain what the GBW product mentioned in line 149 is. It would be nice if they could add the equation of how the GBW product is defined.

7) The authors should describe in the text how much power is taken by the RF directional couplers for the feedback in the klystron loop experimental setup shown in Figure 5a.

8) The authors mention in line 176 that a phase shifter with a wider bandwidth will be used in further investigations. It would be nice if they could express some expectations about what they want to achieve with it.

Author Response

All the answers are in the attached doc file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors reported their results on the design and test of a klystron intra-pulse phase feedback system for electron linear accelerators. The fast intra-pulse feedback of an RF phase is quite important to have the ultimate stability of an electron linear accelerator for applications that require ultra-low timing jitters. The authors succeeded in implementing intra-pulse systems for S- and C-band RF plants. The achieved stability is high. I think this paper is valuable and can be a good reference for intra-pulse phase feedback for normal conducting RF linacs. The manuscript is well organized and no significant modifications are needed for publication. I only have a minor comment. The authors listed the R&D program that has been performed in SPARC_LAB in lines 68-70. I recommend authors add references to these activities if any report is available.

Author Response

All the answers are in the attached doc file.

Author Response File: Author Response.pdf