Evaluation of Bunch Length by Measuring Coherent Synchrotron Radiation with a Narrow-Band Detector at LEBRA
Round 1
Reviewer 1 Report
In this manuscript, the method to evaluate bunch length at an infrared free electron laser is discussed. The bunch length is estimated without destructing the electron beam, and it is important technique. The method is expected to be used for the CSR of synchrotron facility and/or X-ray FEL. It is worth to be published with minor revision.
I would like to suggest English brushup. Sometimes it is difficult to understand the description and it affects the quality of the manuscript.
Figure 8 shows the CSR power vs bunch charge. In lines from 161 to 163, however, only the relation between the bunch length and the charge is discussed. Please resolve such description.
Author Response
Thank you very much for providing important insights.
(1) Figure 8 shows the CSR power vs bunch charge. In lines from 161 to 163, however, only the relation between the bunch length and the charge is discussed. Please resolve such description.
-> We agree that this point requires clarification, and have added the following text: (p.6, lines 162-164).
In other words, the CSR power is not proportional to the square of the charge in the burst mode where the amount of charge per micro-pulse is high.
Thank you once again for your valuable comments and suggestions.
Thank you for your generous consideration.
Reviewer 2 Report
Review Report
- A brief summary (one short paragraph) outlining the aim of the paper and its main contributions.
In this paper, the authors are proposing a method for conducting measurements of electron bunch lengths using a non-destructively technique using the CSR effect. These bunch length measurements, using the CSR technique, are studied and implemented in many accelerator facilities worldwide. Here the authors claim to be the first ones at measuring the root-mean-square (RMS) bunch length with high precision. This is done by considering the detector’s characteristic sensitivity during the observation of the CSR.
- Broad comments highlighting areas of strength and weakness. These comments should be specific enough for authors to be able to respond.
The paper claim in the abstract, i.e. presentation of a “novel technique”, is not developed through the paper in a detailed way. I think this should be the strength of the whole paper but it seems that no technological details are given about the detector. So it is not clear whether this is a commercial device that everybody can purchase or whether it is something developed but the group presenting this article.
- In the Introduction: What is the precision obtained in the measurements? A number would be nice to be placed.
- In the Conclusions: There is no emphasis on the “novel technology” that was indicated in the introduction and I don’t see strength in the authors’ proposed approach of bunch length measurements.
- Specific comments referring to line numbers, tables or figures. Reviewers need not comment on formatting issues that do not obscure the meaning of the paper, as these will be addressed by editors.
I don’t have any specific comment. Everything was well explained and depicted.
Author Response
Thank you very much for providing important insights.
(1) The paper claim in the abstract, i.e. presentation of a “novel technique”, is not developed through the paper in a detailed way. I think this should be the strength of the whole paper but it seems that no technological details are given about the detector. So it is not clear whether this is a commercial device that everybody can purchase or whether it is something developed but the group presenting this article.
-> We agree that this point requires clarification, and have added the following text and the reference: (p.4, lines 95-97, p10, lines 302-304).
This detector is a commercially available Schottky barrier zero bias diode type, which is characterized by small, robust and thermally stable [24].
(2) In the Introduction: What is the precision obtained in the measurements? A number would be nice to be placed.
-> The accuracy of the data used in the calculation is n = 0.68 ± 0.02. Accordingly, we have added the following text to this section: (p.7, lines 200-201).
As we have indicated above, the accuracy of the data used in the evaluation is n=0.68±0.02.
(3) In the Conclusions: There is no emphasis on the “novel technology” that was indicated in the introduction and I don’t see strength in the authors’ proposed approach of bunch length measurements.
-> We agree that this point requires clarification, and have added the following text: (p.8, lines 222-224).
In this method, A commercially available product-based detector can be used to easily evaluate the change in bunch length for each micro-pulse.
Thank you once again for your valuable comments and suggestions.
Thank you for your generous consideration.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The authors claim that they may reconstruct the pulse duration of a beam starting from the spectral modification of the emitted CSR radiation as a function of the beam charge. They correlate the spectral change to the charge, as if the charge is the only parameter into play. I expect the bunch length to be correlated to the CSR spectral properties, reconstructing the longitudinal distribution of charge from the entire spectrum. Now the procedure proposed is based on the determination of the spectral content as a function of the charge, but the charge induces several modification to the beam dynamics as a change in the beam envelope, the beam emittances and the duration and the longitudinal shape. I am skeptical that this is possible with a simple relation as the one proposed and used by the authors. Unfortunately I could not understand more, because of the missing definitions, the poor description of the method and the setup, and last but not least, the English language which should be improved.Author Response
Dear Reviewer,
Thank you for providing these insights.
Although we are now doing our best to revise condensedmatter-712619, we are unable to send the revised manuscript by the due date. We have found that we need a lot of modifications for the complete revision and they will take a while.
We realized the submission delay will cause some inconveniences for you, we would be grateful if you could extend the deadline by 7 March 2020. Your understanding and kind support will be appreciated.
Kind regards,
Takeshi Sakai
Reviewer 2 Report
The paper is dedicated to the development of technique to the measurements an electron bunch length (RMS value) if the shape of the bunch is well known. The authors looked at a particular case of a Gaussian bunch. The authors suggested that to measure the bunch length a measurement of the CSR signal amplitude at a single frequency should be sufficient. In the ideal case if: the bunch charge is accurately measured (no errors), the bunch has a pure Gaussian shape i.e. it is not a combination of two Gaussian functions which would describe rise and decay times, there is no background noise and all components are well calibrated, it may be possible. However, if a single condition from the list above is not satisfied this will not be possible.
The paper has several major faults:
English is very unclear and it has to be improved significantly before the publication References are not representing near enough the efforts made by the international scientific community to design single shot bunch profile monitor i.e. to measure the bunch length The statements made by authors like “…we succeeded in measuring the root-mean-square bunch length with high precision…” are not proven i.e. no results of alternative measurements of the same parameter are given to compare. In the experiments the authors used components like quartz window, but no RF characteristics (absorption/transmission) of the window in the frequency range of the interest are provided. Same issue with other components of the experiments including the mirror. According to the description of the experiment after the output window the CSR signal propagates through the air and the air absorption in this frequency range can be strong. No analysis of the air absorption is given. In the text a number of parameters is introduced but not well defined for example Se , this should be carefully checked prior to the submission. I am still not sure at which frequency the experiments were carried out. It looks like the whole frequency range [92-102] available to the detector plus band-pass filter system was used. The band width is 10GHz and it is not narrow to justify the expression (5). The reason to introduce (5) is unclear.
There is a number smaller errors but there is no points to consider smaller errors while the main issues are not resolved.
Author Response
Dear Reviewer,
Thank you for providing these insights.
Although we are now doing our best to revise condensedmatter-712619, we are unable to send the revised manuscript by the due date. We have found that we need a lot of modifications for the complete revision and they will take a while.
We realized the submission delay will cause some inconveniences for you, we would be grateful if you could extend the deadline by 7 March 2020. Your understanding and kind support will be appreciated.
Kind regards,
Takeshi Sakai
