Investigation on High-Efficiency Beam-Wave Interaction for Coaxial Multi-Beam Relativistic Klystron Amplifier

Round 1

Reviewer 1 Report

Dear Authors,
Your work, in my subjective opinion, is a study, the results of which deserve publication practically unchanged. This is extremely rare, but you have achieved such results in this manuscript. The only thing that needs to be changed is the size of the pictures in the text. Some of them are not large enough for the convenience of the readers.

Author Response

Dear Editor,

Thank you very much for sending us the valuable comments on our paper entitled “Investigation on high efficiency beam wave interaction for coaxial multi-beam relativistic klystron amplifier” (Manuscript ID: electronics-1525152). We have carefully responded to the comments accordingly. Our point-by-point responses are listed below.

 

ASSISTANT EDITOR:

Reply to Assistant Editor:

We express our sincere thanks for the work on our manuscript. We have, in the revised manuscript, responded to all questions and issues raised by the reviewer. Also, we have highlighted the changes and modifications while addressing the reviewers’ points in the revised manuscript.

 

REVIEWER #1:

Comments:

Your work, in my subjective opinion, is a study, the results of which deserve publication practically unchanged. This is extremely rare, but you have achieved such results in this manuscript. The only thing that needs to be changed is the size of the pictures in the text. Some of them are not large enough for the convenience of the readers.

Reply:

We express our sincere thanks for appraising our manuscript to be interesting. We have modified the size of the pictures in the revised manuscript. They are Figure2, Figure3, Figure7, Figure8, Figure9, and Figure10.

 

Finally, we have further revised the full text and the revised parts are marked in RED. Kindly please check!

 

Finally, on behalf of all the co-authors, I gratefully acknowledge the Editor and Reviewers for their constructive comments and precious time!

 

Yours sincerely,

Shifeng Li

 

No. 64, Mianshan Road, Mianyang 621900, China

Science and Technology on High Power Microwave Laboratory, Institute of Applied Electronics, China Academy of Engineering Physics,

E-mail: lishifeng@alu.uestc.edu.cn

Tel: +86-816-2484540

Reviewer 2 Report

On my opinion, this is an interesting paper describing a design of a powerful multi-beam klystron. The paper is clearly written and includes interesting results of optimization of the multi-cavity system. The paper can be accepted for the publication, but the Authors should take into account the following comments.

1. Abstract: “ … external quality factor of output cavity …”

The term “external Q-factor” appears also in the text. I think that the Authors should give somewhere in the text a brief explanation of the meaning of this term.

2. Lines 91-93: “It is shown that efficiency will increase non-linearly as the number of cavities increases [13]. When the number of cavity is greater than 5, the efficiency increases slowly. Therefore, we set  the number of cavity to be 5.”

I don't think that "five cavities" is a world constant. Probably, the optimal number of cavities depends on many parameters of the system (for example, the intensity of the electron-wave interaction, gain factor, spread in the electron beam, etc.). The calculations given in work [13] are just one of the possible examples of optimization for a particular system. It would be useful if the authors would give some more specific justification for this figure in the paper (for example, the proximity of some characteristics of their system and the system considered in work [13]).

3. Lines 94-96: “The effects of structural parameters (Lcavity, Lgap, Rout, and Rin) of the cavity on high-frequency parameters (M, f , and R/Q) are investigated, and the results are shown in Figure 2. “

I think, this are results of simulations? Then,  a description of the simulation model (or the used code) is needed here.

4. Line 99: “In addition, the equivalent circuit of the coaxial resonant cavity is an RLC circuit, as shown in Figure 3(a).”

I think many readers will be puzzled by the unexpected appearance of a fairly simple oscillatory circuit here, as well as its equivalence to the system considered in the article. If the authors believe that the analogy with the oscillatory circuit is really useful to readers, then it should be explained where this circuit comes from and what the analogy consists of.

5. Line 119: “AJDISK is a 1-D large-signal numerical simulation software based on the disc model”.

Detailed explanation of this code is needed (including referenced to papers describing this code, as well as to papers where this code  has been used).

5. Figure 4 and 5.

These figures give results of optimizations of the system over five parameters (fice frequencies in fig. 4 and five lengths in fig. 5). I do not understand how these optimizations were carried out? For instance, maybe, the authors changed one of five frequencies whereas the other four were fixed?

6. Lines 169-172: “The 3-D PIC simulation is more in line with the actual model of CMB-RKA and the software we used is CHIPIC which can clearly analyze the bunching process of the electron beam and the physical nature of the high-efficiency beam-wave interaction. “

Here I would like to make a comment similar to comment 4.

Author Response

Dear Editor,

Thank you very much for sending us the valuable comments on our paper entitled “Investigation on high efficiency beam wave interaction for coaxial multi-beam relativistic klystron amplifier” (Manuscript ID: electronics-1525152). We have carefully responded to the comments accordingly. Our point-by-point responses are listed below.

 

ASSISTANT EDITOR:

Reply to Assistant Editor:

We express our sincere thanks for the work on our manuscript. We have, in the revised manuscript, responded to all questions and issues raised by the reviewer. Also, we have highlighted the changes and modifications while addressing the reviewers’ points in the revised manuscript.

 

REVIEWER #2:

Comments:

On my opinion, this is an interesting paper describing a design of a powerful multi-beam klystron. The paper is clearly written and includes interesting results of optimization of the multi-cavity system. The paper can be accepted for the publication, but the Authors should take into account the following comments.

Reply:

Our gratitude is due to the reviewer for appreciating our work and immensely motivating us by encouraging comments.

 

Question 1:

Abstract: “ … external quality factor of output cavity …”

The term “external Q-factor” appears also in the text. I think that the Authors should give somewhere in the text a brief explanation of the meaning of this term.

Answer 1:

We would like to thank the reviewer for the suggestion. A brief explanation of the external Q-factor was added in lines 166-168 as “In the output cavity, the Q_ext was used to describe its coupling with the external coupler waveguide, and relate closely to its gap voltage to decelerate the modulated electrons sufficiently.”.

 

Question 2:

Lines 91-93: “It is shown that efficiency will increase non-linearly as the number of cavities increases [13]. When the number of cavity is greater than 5, the efficiency increases slowly. Therefore, we set the number of cavity to be 5.”

I don't think that "five cavities" is a world constant. Probably, the optimal number of cavities depends on many parameters of the system (for example, the intensity of the electron-wave interaction, gain factor, spread in the electron beam, etc.). The calculations given in work [13] are just one of the possible examples of optimization for a particular system. It would be useful if the authors would give some more specific justification for this figure in the paper (for example, the proximity of some characteristics of their system and the system considered in work [13]).

Answer 2:

We would like to thank the reviewer for attention to the unclear expression. In the revised manuscript, we have modified the expression in lines 90-93 as” And Ref [13] researched the maximal efficiency of two multi-beam klystrons (7-beams and 42-beams) that their efficiency all increased non-linearly as the number of cavities increased. When the number of cavities is greater than 5, the efficiency increases slowly.”.

 

Question 3:

Lines 94-96: “The effects of structural parameters (L_cavity, L_gap, R_out, and R_in) of the cavity on high-frequency parameters (M, f, and R/Q) are investigated, and the results are shown in Figure 2.” I think, this are results of simulations? Then, a description of the simulation model (or the used code) is needed here.

Answer 3:

We would like to thank the reviewer for the useful proposal. The simulation model has been shown in Figure 1. We have been added the description of the simulation software in lines 95-97 as “The effects of structural parameters (L_cavity, L_gap, R_out, and R_in) of the cavity on high-frequency parameters (M, f, and R/Q) are simulated in 3D EM analysis software (CST Studio Suite) [25], and the results are shown in Figure 2.”.

Question 4:

Line 99: “In addition, the equivalent circuit of the coaxial resonant cavity is an RLC circuit, as shown in Figure 3(a).”

I think many readers will be puzzled by the unexpected appearance of a fairly simple oscillatory circuit here, as well as its equivalence to the system considered in the article. If the authors believe that the analogy with the oscillatory circuit is really useful to readers, then it should be explained where this circuit comes from and what the analogy consists of.

Answer 4:

We would like to thank the reviewer for attention to unclear expression. In the revised manuscript, the expression has been modified in lines 100-103 as “In addition, the equivalent circuit of the coaxial resonant cavity is an RLC circuit, as shown in Figure 3(a). L and C represent the high-frequency characteristics of the toroidal and parallel-plate portion in the cavity, R represents the electronic beam load, external load, and cavity wall loss.”.

 

Question 5:

Line 119: “AJDISK is a 1-D large-signal numerical simulation software based on the disc model”.

Detailed explanation of this code is needed (including referenced to papers describing this code, as well as to papers where this code has been used).

Answer 5:

We would like to thank the reviewer for the suggestion. In the revised manuscript, the detailed explanation and reference of AJDISK has been added in lines 122-128 as “AJDISK is a 1-D large-signal numerical simulation software developed at SLAC and based on the disc model, which is adapted to simulate klystrons with a single cylindrical and sheet beam [27]. Thus, when it was used to analyze the high-efficiency beam-wave interaction of CMB-RKA, the equivalent has to be done. In AJDISK simulation, the R/Q is 14 times the CMB-RKA and the beam current is 300 A that 1/14 times the CMB-RKA, the other parameters, such as M, beam voltage, f_n, beam radius, drift tube radius, input power, Q_ext, and l_n, keep the same with the CMB-RKA.”.

 

Question 6:

Figure 4 and 5.

These figures give results of optimizations of the system over five parameters (five frequencies in fig. 4 and five lengths in fig. 5). I do not understand how these optimizations were carried out? For instance, maybe, the authors changed one of five frequencies whereas the other four were fixed?

Answer 6:

We would like to thank the reviewer for attention to unclear expression. In the revised manuscript, the details of the optimization method have been added in lines 128-130 as “Besides, the single variable method was taken in the whole process of the research. It means that only one parameter was changed whereas the others were fixed.”.

 

Question 7:

Lines 169-172: “The 3-D PIC simulation is more in line with the actual model of CMB-RKA and the software we used is CHIPIC which can clearly analyze the bunching process of the electron beam and the physical nature of the high-efficiency beam-wave interaction.” Here I would like to make a comment similar to comment 4.

Answer 7:

We would like to thank the reviewer for the suggestion. In the revised manuscript, the detailed explanation and reference of CHIPIC have added in lines 176-181 as “The 3-D PIC simulation is more in line with the actual model of CMB-RKA and the software we used is CHIPIC which was developed at the University of Electronic Science and Technology of China and was proved a validity electromagnetic PIC code [28]. It can clearly analyze the bunching process of the electron beam and the physical nature of the high-efficiency beam-wave interaction.”.

 

Finally, we have further revised the full text and the revised parts are marked in RED. Kindly please check!

 

Finally, on behalf of all the co-authors, I gratefully acknowledge the Editor and Reviewers for their constructive comments and precious time!

 

Yours sincerely,

Shifeng Li

 

No. 64, Mianshan Road, Mianyang 621900, China

Science and Technology on High Power Microwave Laboratory, Institute of Applied Electronics, China Academy of Engineering Physics,

E-mail: lishifeng@alu.uestc.edu.cn

Tel: +86-816-2484540

Reviewer 3 Report

This is a very well written and informative paper, and I have no issue with accepting it for publication after some very minor suggestions/additions, which I feel could improve an already good manuscript.

Section 1:

1. Line 23-24: reference to review paper on RKA if it exists?

Section 2:

• Line 73-74: Missing "represented as a δ function"?
• Line 84: Unnecessary "And".
• Line 91-92: Here the authors discuss the number of cavities above 5 having little effect on efficiency. It might be nice to show the diminishing effect in efficiency improvement as a plot?
• Line 95: How is the coupling parameter, M, calculated?

Section 3:

• Line 119: suggest a reference to AJDISK, A. Jensen et al, IEEE TED, 61(6), 2014.
• Line 121-123: slight rewording to clarify that AJDISK is only simulating a single beam, and so the R/Q and beam current are changed.
• Line 129-130: Not sure what the sentence "As a result...anti-buunching electrons." is referring to?
• Line 135-141, Figur3 4: Perhaps being pedantic, but I found it confusing to refer to idler cavity I, cavity I, and input cavity. This could confuse a reader, and could be addressed by referring to them as "input cavity, cavity 2, cavity 3..., output cavity".
• Figure 4 & 5: Are these curves calculated with all other parameters (other than resonant freuuqnecy in figure 4, and drift length in figure 5)  remaining fixed? If so, it could be useful to say this explicitly in the captions.
• Figure 6: It might be worth adding some data points to the figure to indicate which values of Qext where examined?
• Line 170: Reference to CHIPIC?

Section 4:

• Figure 9 & 10: In the phasespace plots, a small number of spent electrons (slow velocity after output cavity) are seen at the end of the geometry. Do these affect the device over long time periods?
• Line 213-216: Here the authors discuss reflected electrons - does the output power remain stable even with reflected electrons, or does it become very oscillatory? In addition, have longer runs been performed to ensure the klystron is stable over long periods of time?
  
  
• Figure 11: Add the input power for the generated waveform caption, indicating efficiency, gain and input power.

Author Response

Dear Editor,

Thank you very much for sending us the valuable comments on our paper entitled “Investigation on high efficiency beam wave interaction for coaxial multi-beam relativistic klystron amplifier” (Manuscript ID: electronics-1525152). We have carefully responded to the comments accordingly. Our point-by-point responses are listed below.

 

ASSISTANT EDITOR:

Reply to Assistant Editor:

We express our sincere thanks for the work on our manuscript. We have, in the revised manuscript, responded to all questions and issues raised by the reviewer. Also, we have highlighted the changes and modifications while addressing the reviewers’ points in the revised manuscript.

 

REVIEWER #3:

Comments:

This is a very well written and informative paper, and I have no issue with accepting it for publication after some very minor suggestions/additions, which I feel could improve an already good manuscript.

Reply:

Our gratitude is due to the reviewer for appreciating our work and immensely motivating us by encouraging comments.

 

Question 1:

Line 23-24: reference to review paper on RKA if it exists?

Answer 1:

We would like to thank the reviewer for the advice. The reference to review paper on RKA has been added in lines 23-24 as “RKA no longer pursues power improvement but focuses on miniaturization, high efficiency and low power consumption [11].”

 

Question 2:

Line 73-74: Missing "represented as a δ function"?

Answer 2:

We would like to thank the reviewer for the suggestion. The missing expression have been added in lines 73-74 as “which means the density of modulated beam is well represented as a δ function.” in the revised manuscript.

 

Question 3:

Line 84: Unnecessary "And".

Answer 3:

We would like to thank the reviewer for the suggestion. “And” have been deleted in line 84 in the revised manuscript.

 

Question 4:

Line 91-92: Here the authors discuss the number of cavities above 5 having little effect on efficiency. It might be nice to show the diminishing effect in efficiency improvement as a plot?

Answer 4:

We would like to thank the reviewer for the useful advice. Ref [13] researched the maximal efficiency of two different multi-beam klystrons. The plot of their relationship is shown in Ref [13]. Readers can get the plot by reading Ref [13]. Meanwhile, in the revised manuscript, we have modified the expression in lines 90-93 as” And Ref [13] researched the maximal efficiency of two multi-beam klystrons (7-beams and 42-beams) that their efficiency all increased non-linearly as the number of cavities increased. When the number of cavities is greater than 5, the efficiency increases slowly.”.

 

Question 5:

Line 95: How is the coupling parameter, M, calculated?

Answer 5:

Firstly, . Secondly, we can obtain the distribution of E_z along the centerline of the cavity gap through simulation in CST Studio Suite software. Lastly, we write the code based on the equation M and the simulation result of E_z to attain the value of M.

 

Question 6:

Line 119: suggest a reference to AJDISK, A. Jensen et al, IEEE TED, 61(6), 2014.

Answer 6:

We would like to thank the reviewer for the useful advice. In the revised manuscript, a reference to AJDISK have added in lines 122-128 as “AJDISK is a 1-D large-signal numerical simulation software developed at SLAC and based on the disc model, which is adapted to simulate klystrons with a single cylindrical and sheet beam [27].”.

 

Question 7:

Line 121-123: slight rewording to clarify that AJDISK is only simulating a single beam, and so the R/Q and beam current are changed.

Answer 7:

We would like to thank the reviewer for his/her better expression. The expression has changed in lines 122-128 as “AJDISK is a 1-D large-signal numerical simulation software developed at SLAC and based on the disc model, which is adapted to simulate klystrons with a single cylindrical and sheet beam [27]. Thus, when it was used to analyze the high-efficiency beam-wave interaction of CMB-RKA, the equivalent has to be done. In AJDISK simulation, the R/Q is 14 times the CMB-RKA and the beam current is 300 A that 1/14 times the CMB-RKA, the other parameters, such as M, beam voltage, f_n, beam radius, drift tube radius, input power, Q_ext, and l_n, keep the same with the CMB-RKA.”.

 

Question 8:

Line 129-130: Not sure what the sentence "As a result...anti-bunching electrons." is referring to?

Answer 8:

Electrons of the bunching beam can be divided into bunching and peripheral (anti-bunching) electrons. When they enter into the gap of the detuning cavity, the electrons within the bunching core will be modulated weakly compared to the anti-bunching electrons.

 

Question 9:

Line 135-141, Figur3 4: Perhaps being pedantic, but I found it confusing to refer to idler cavity I, cavity I, and input cavity. This could confuse a reader, and could be addressed by referring to them as "input cavity, cavity 2, cavity 3..., output cavity".

Answer 9:

We would like to thank the reviewer for his/her advice. In the revised manuscript, idler cavity I, cavity II, and cavity III have been modified as cavity 2, cavity 3, and cavity 4.

 

Question 10:

Figure 4 & 5: Are these curves calculated with all other parameters (other than resonant frequency in figure 4, and drift length in figure 5) remaining fixed? If so, it could be useful to say this explicitly in the captions.

Answer 10:

We would like to thank the reviewer for his/her attention to unclear expression. We changed only one parameter whereas the others were fixed. In the revised manuscript, the details have been cleared in lines 128-130 as “Besides, the single variable method was taken in the whole process of the research. It means that only one parameter was changed whereas the others were fixed.”.

 

Question 11:

Figure 6: It might be worth adding some data points to the figure to indicate which values of Q_ext where examined?

Answer 11:

We really appreciate the reviewer’s suggestions. Data points to the Figure 6 have been added in the revised manuscript.

 

Question 12:

Line 170: Reference to CHIPIC?

Answer 12:

We would like to thank the reviewer for the suggestion.

In the revised manuscript, the detailed explanation and reference of CHIPIC have added in lines 176-181 as “The 3-D PIC simulation is more in line with the actual model of CMB-RKA and the software we used is CHIPIC which was developed at the University of Electronic Science and Technology of China and was proved a validity electromagnetic PIC code [28]. It can clearly analyze the bunching process of the electron beam and the physical nature of the high-efficiency beam-wave interaction.”.

 

Question 13:

Figure 9 & 10: In the phasespace plots, a small number of spent electrons (slow velocity after output cavity) are seen at the end of the geometry. Do these affect the device over long time periods?

Answer 13:

These spent electrons would collide with the wall of the output cavity and electron channel, to reduce the life of the device.

 

Question 14:

Line 213-216: Here the authors discuss reflected electrons - does the output power remain stable even with reflected electrons, or does it become very oscillatory? In addition, have longer runs been performed to ensure the klystron is stable over long periods of time?

Answer 14:

First, the output power remains stable or not, it is decided from the number of reflected electrons. As shown in Figure 10, when the input power is above 3.7 kW, the number of reflected electrons is very large, resulting in a serious decline in output power. If the reflection of the electrons is slight, the output power does not drop too much, or it remains stable. Second, the simulation time is 80ns, which has long enough to ensure the klystron is stable over long periods of time.

 

Question 15:

Figure 11: Add the input power for the generated waveform caption, indicating efficiency, gain and input power.

Answer 15:

We would be deeply grateful to the reviewer for the advice. In the revised manuscript, the input power for the generated waveform caption has been added in Figure 11.

 

Finally, we have further revised the full text and the revised parts are marked in RED. Kindly please check!

 

Finally, on behalf of all the co-authors, I gratefully acknowledge the Editor and Reviewers for their constructive comments and precious time!

 

Yours sincerely,

Shifeng Li

 

No. 64, Mianshan Road, Mianyang 621900, China

Science and Technology on High Power Microwave Laboratory, Institute of Applied Electronics, China Academy of Engineering Physics,

E-mail: lishifeng@alu.uestc.edu.cn

Tel: +86-816-2484540

Round 2

Reviewer 2 Report

On my opinion, the revised version of the paper can be accepred for the publication.