Selective Photonic-Structure Cavity for High-Cyclotron-Harmonic Gyrotrons
Round 1
Reviewer 1 Report
The article is devoted to the actual topic of creating high-frequency gyrotrons operating on the harmonics of the cyclotron frequency. The method proposed by the authors for using diffraction gratings as the side wall of the optical resonator of the gyrotron provides the generation of a selected higher harmonic and the suppression of lower-frequency harmonics, including the fundamental one, due to a much higher quality factor of this selected harmonic in the optical resonator. The article is certainly of interest to gyrotron developers and corresponds to the profile of Photinics.
However, the article contains many inaccuracies and typos that should be corrected.
I would also like to make a few remarks on physics, the consideration of which, in the opinion of the reviewer, would improve this material.
Physics Notes:
1) The electrons in Fig.2 must rotate in the opposite direction for a given direction of the magnetic field.
2) The paragraph with lines 117-120 contains the wrong conclusion of the authors. It has been known since the time of Robert Wood that the most efficient grating is the one whose gloss angle coincides with angle of working order of diffraction. In geometry of this article, this corresponds to a rectangular geometry with certain geometric parameters. A sinusoidal geometry (like any other periodic structure) will have less efficiency due to the reflection of radiation into many other diffraction orders. It is clear that the sharp corners of the rectangular structure give an increase in the field strength. Therefore, they must be rounded with a minimum radius so as not to greatly reduce the diffraction efficiency.
Moreover, if you look at the enlarged geometry of the authors' drawings, then they show exactly a rectangular structure with smoothed corners, and not sinusoidal geometry.
Moreover, the true sinusoidal geometry is used by the authors on the upper gratings of Fig. 8e). And this mirror, as follows from the physics of diffraction gratings, reflects not only into the working first order of diffraction, but also into the so-called zero order, at an angle of 90 degrees to the first. This zero order is used by the authors to extract radiation. The authors call this method of radiation output “elegant” (lines 306-307), but say nothing about its simple physical nature.
3) The use of polymer diffraction gratings (line 321) looks doubtful for stationary high-power generation. Perhaps the words "low power" or "impulse" should be added?
Formatting and typos:
1) On Fig.1e,f should be hII instead of kII.
2) Line 55: Nop=0 corresponds to ωop=0 according to (1). You probably need Nop=1 and ωop≈Ω.
3) Correct sloppiness in Fig1a): lines, arrows, etc.
4) Rotate Fig.1d, Fig.3 left, Fig.8b,c) clockwise by 45 degrees so that this geometry would be similar to Fig.2,3,4,5. The mental reversal greatly strains the readers.
5) Add the letter "A" to the right green curve in Fig. 5, where the changes in h are indicated. Make this curve look like the true left green curve.
6) Add numbers to the color scale in Fig. 3.7.
7) You should draw in Fig.2 the dimensions: a0, d0, h0. In this picture, measure "k" on "kopl". It is not parallel to the mirrors (line 145).
8) Line 150: replace "Fabri-Perot" with "Fabry-Perot".
9) Line 154: replace "second and third cyclotron harmonic" with "second and third cyclotron subharmonic".
10) The words “photonic structure” (line 299) are less informative than the words “diffraction grating”.
Comments for author File: 
Comments.pdf
Author Response
A file with our response to all referees' comments is attached.
Author Response File: 
Author Response.docx
Reviewer 2 Report
In the manuscript entitled “”Single-Frequency” Photonic-Structure Quasi-Optical Cavity for High-Cyclotron-Harmonic Gyrotrons”, the authors have modeled a photonic cavity (comprising two parallel corrugated mirrors) for improved mode selectivity of gyrotrons. The authors claim that the system looks quite realistic at a first glance. However, from my point of view, some details are missing. The authors used some material parameters without any reference to a specific material. For example, the metal conductivity that the authors used 1.4E7 S/m is associated to a particular material? Is a hypothetical value? Moreover, I didn’t see the amplitude of the field B. Is the amplitude used by the authors in agreement with recent literature?
Another important point is the title. From my point of view, the title seems like a set of words without any meaning. It is important to emphasize this issue because the title should provide the reader with a clear idea of the content in this work.
The presentation of the manuscript, in particular, the introduction should also be improved to better justify the simplifications that the authors are doing in this work. In particular, giving the reader a more convincing arguments to use a simple 2D model for the system.
Author Response
A file with our response to all referees' comments is attached.
Author Response File: Author Response.docx
Reviewer 3 Report
This paper described a novel quasi-optical cavity based on corrugated mirrors that may be pave the way to develop gyrotron. This research is interesting. However, due to some important parts are not clear in the manuscript, there are some important points I recommend to clarify.
1. I suggest authors present a 3D view to make the cavity structure more clearly. The mirror boundaries, open boundaries, and absorbers of the cavity also should be pointed. If the electron trajectory would be presented, that will be better.
2. Line 126 and 131, the a0 , d0 and h0 should be introduced in detail.
3. In fig 2.(b), orbit of electrons in the cavity is shown, this is the transverse section view, a longitudinal section view should also be presented. Or, this is just 2D simulation? I also suggest add an additional fig. 2(c) in fig. 2 which presents the vector direction of E field in the cavity.
4. The coupling efficiency between electrons and electromagnetic field of this cavity is very important, can authors have a try to give the coupling efficiency or elaborate the mechanism.
5. Each of a model is consist of ‘absorbers’ at the left and right port, so more details should be given about the simulation in HFSS.
6. In fig 8, an output system is given, a Gaussian beam is shown at the output port of the transverse section. It is necessary to give a complete model including this output system and interaction cavity.
Editing comments
7. Fig 1, line 71, the fig .1(d) should be fig .1(f).
Author Response
A file with our response to all referees' comments is attached.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors have addressed all my previous concerns. I recommend publishing the manuscript in its current form.
Reviewer 3 Report
The authors revised their manuscript according to the comments. So I recommend accepting the revised manuscript.
