Faraday Cups: Principles, Designs, and Applications Across Scientific Disciplines—A Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Some comments and recommendations for the manuscript

instruments-3760251

10. July. 2025

 

This manuscript is a review article on Faraday Cups (FCs), in which not only principles and designs but also many applications, antimatter research, mass spectroscopy, broad ion beam measurements, space propulsion, fusion reactors, nuclear, particle, and high-energy physics, medical accelerators, etc., along with recent and future technological advancements, are given in detail. This review article may help young researchers, engineers and to say nothing of experts to start FC designs in wide applications.

I believe that this article gives an excellent review to fundamental designs of FCs at a starting point in many applications. This article is described by a clear discussion and plain English. However, I will give following questions and some minor comments as a reader of the interesting article, although the summarized review is very interesting. I recommend this article to publish in Instruments (MDPI).

 

Minor suggested points

• In eq.(3) of section 3 in p.6, the sputtering yield \gamma_{sput} is defined. However, in Fig.3, Fig.4 and Fig.5 of section 3, a similar parameter “sputter yield (S)” is used without any definition. It is ambiguous that these two parameters have the same definition. Please check it.
• In eq.(5) of section 3 in p.6, a comma should be put not at the end of denominator, but the end of equation. Please check it.
• In Fig.7 of section 3.1.1 in p.8, it can be seen that clear two peaks are around 100 eV. It is ambiguous which peak corresponds to EBP or that both the peaks correspond to EBP. Please check it.
• In the 236^th line of section 3.1.1 in p.10, it is seen that there is an additional “along”.
• In the 246^th to 270^th lines of section 3.1.1 in p.11, it may be difficult to understand the detailed explanations without any drawings. It may be better to insert even simple drawings.
• In eq.(8) of section 3.1.1 in p.12, the scattering angle \theta^’ is defined, and however, in the 277th line, the angle is indicated by \theta without any symbol dash. Please check it.
• In the 280th to 281th lines, you mention that the scattering cross section scales as 1/E^2 at high energies, and however, in eq.(8), it scales as 1/E. Please check it.
• In Fig.10(a) of section 3.1.1 in p.13, the legend in the right-hand side may be missed. Please insert its legend.
• In Fig.12 of section 3.1.2 in p.15, it may be better to use a clearer drawing because it is unclear to read the numerical value of the target depth.
• In the 347th line of section 3.1.2 in p.15, you mention on “CFD analysis” without any description. It is better to stand for the abbreviation.
• In the 259th to 260th lines, you mention on “Allison type scanner”. It may be better to refer to a related reference.
• In Table 3 of section 3.1.2 in p.17, it may be better to unify the font in “pbar/p/e-“ of the 1^st line because the font of “pbar” is different from others. Please check it.
• In the 283th to 285th lines of section 3.1.3 in p.18, it may be better to be revised to “The critical energy, where …. is equal, is given by ….”.
• In the 409th line of section 3.1.3 in p.18, it may be better to be revised to “For magnetic fields: High-permeability alloys (…), Composite materials ….”.
• In Fig.15 of section 3.1.3 in p.18, it seems that there are too fewer explanations. For example, what is a solid blue circle around the center location?, what is the solid red circle inside the alloy?, what does the double shielding mean?, etc., although you refer to a reference.
• In eq.(12) of section 4.1.1 in p.20, there is a mistake in the equation. That is, it shows \Delta V=\sqrt{4k_BRT/t_m}. Please check it.
• In Fig.18 of section 4.1.2 in p.21, there are no figure indicators, (a) and (b).
• In eq.(13) of section 4.1.3 in p.22, it may be better to be revised to V_{out}=-\frac{1}{RC}…, which shows a mathematical fraction style.
• In Fig.20 of section 4.1.3 in p.22, the feedback capacitor is shown by “Cf”, and however, it is described by “C” (see the 499^th line).
• In the 526^th to the 527^th lines of section 4.1.3 in p.23, it may be better to refer National Instrument, Xilinx, Altera to each reference(web site), while only the web site of CAEN is referred.
• In a case of 2x Frequency of Fig.21 of section 4.1.4 in p.24, it may be pedagogically better to superimpose another low frequency aliasing wave in the figure.
• In the 597^th line of section 4.2.3 in p.25, it may be better to refer to a reference for “CERN White Rabbit” timing modules.
• In the 620^th to 621th lines of section 4.2.5 in p.25, it may be better to refer to web sites, “LabVIEW” and “MATLAB”.
• In the 631^th line of section 5 in p.25, it may be better to be revised to “… the voltage reflection coefficient (\rho_v)” given ….
• In the 634^th and 636^th lines of section 5 in p.26, it should be specified by “Z=0” for short circuit and by “Z=\infty” for open circuit“, respectively.
• In up to the 636^th lines of section 5 in p.26, there are some descriptions on impedance matching for fast FC signals, and however, there are only descriptions on three matching conditions, that is, perfect matching, short circuit, and open circuit. It seems they are too short explanations. I suggest an idea to add a drawing including fast signal waveforms with and without any reflection signal, for example.
• In any explanations and discussions following the 641^th line of section 5 in p.26, including eqs. (16) and (17), any geometrical parameters, kappa, alpha, d, and L are not clearly defined, and thus, it is difficult to understand or follow any following explanations. It may be better to define these parameters with some drawings.
• In the 664^th line of section 6 in p.27, it may be better to be revised to “… is very limited in various experiments [140-144]”.
• In Fig.23 of section 6 in p.27, it is difficult to recognize any colored lines, which are too light. It may be better to use deeper colors for the lines.
• In the 689^th line of section 6 in p.28, it seems to be a strange style [151?-155]. Please check it.
• In the 690^th line of section 6 in p.28, it may be better to be revised to “… known 100~k(not italic but roman k)\Omega”. Please check it.
• In the 696^th and 698th lines of section 6 in p.28, it is difficult to understand the sentence, “Electrons deposit their ….. to release secondary electrons” and thus, it should be clearly described.
• In Fig.26(b) of section 8 in p.31, there may be a misprint “Minimum and ….”.
• In Fig.27(a) of section 8 in p.32, there may be a misprint “l_b (FC) (mA)”. In the figure, \sigma_{cx}:3.0x10^-15 cm^2 is indicated. Its scale 10^-15 may be wrong?, because it is too small. Please check it.
• In the 790^th line of section 8 in p.32, there may be a misprint “l_b (FC)”. Please check it.
• In the 798^th line of section 8 in p.33, it seems that an erf function is not defined anywhere. Please check it.
• In Fig.28(b) of section 8 in p.33, it seems that the quality of the figure is not so good. It may be better to replace it to more qualitavely good one.
• In the 819^th and 825^th lines of section 8.0.1 in p.34, you describe on the collimated FC by showing Fig. 29 (c), and however, it is not shown anywhere. Fig.29(c) may correspond to Fig.29(b) or it may be missing. Please check it.
• In the caption of Fig.30 of section 8.0.2 in p.35, the authors, Okamoto et al.?, may be missing.
• In the 866^th line of section 8.0.2 in p.35, it may be better to be revised to “the value of neutral flux \gamma_0 can be determined ….”.
• In “Beam Intensity Measurement” of section 9.1.1 in p.36, it may be better to add another drawing, which shows a measurement setup as shown in Fig.32.
• In Fig.33 of section 9.1.1 in p.37, it is difficult to recognize the black-colored letters “Faraday Cup” in the figure, because the background color is deep blue. It may be better to use white or blight color.
• In section 9.1.3 in p.38, it is unclear that in “Monitoring beam quality” and “Optimizing accelerator performance”, nondestructive beam diagnostics are generally required without destroying any beams, and however, FCs are based on destructive principle. It is better to give careful explanation to perform them.
• In Fig.34 of section 9.2.1 in p.39, it is difficult to understand the experimental setup because there are no explanations to any devices (Fig.34(a)). It is also ambiguous to recognize the intensity profile (Fig.34(c)), for that which dashed line contributes (Fig.34(b)). It is better to clarify it.
• In the 1095^th line of section 10 in p.43, it is better to insert unit in or 0.4 [211] because of the unit missing.
• In the 1112^th line of Conclusion in p.45, it may be a misprint (a period missing) “at low beam current, etc., …”.
• In the list of Abbreviations in p.46, KEK Ko Energy-kasokuki Kenkyukiko

Comments for author File: Comments.pdf

Author Response

Thank you for your positive feedback and for identifying corrections to improve the review article. We have carefully reviewed and incorporated your suggestions to enhance the clarity and overall quality of the manuscript

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article is a good review, with an adequate bibliography.

I have no particular concerns about the content or form of the manuscript.

The work will be useful for students and newcomers to the field of beam diagnostics, particularly regarding the topic of Faraday cups.

Author Response

We would like to thank the referee for their positive feedback and comments.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Some comments and recommendations for the manuscript instruments-3760251.v2

19. Aug. 2025

 

After reading the revised article, I think that it has been revised in a quite satisfactory way because the argument has become clearer than that of the previous one. This review report is very interesting because such fundamental and technical review summary and discussions on FCs for present and also future various accelerator technologies are important.

I believe that this paper gives an important step to wider applications in accelerators and other disciplines. I strongly recommend this article to publish in Instruments.

Finally, I point out a few minor revisions to be revised before publication.

• In the 151^th line of p. 6 of the revised manuscript, it seems that the approximation condition may be correct in not 0.2\lesssim Z_t/Z_i \gtrsim 5 but 0.2\lesssim Z_t/Z_i \lesssim 5. Please check it.
• In the 301^th line of p. 12 of the revised manuscript, it may be better to be revised that “… … E_{bs} is proportional to the incident energy and …”. Please check it.
• In the 696^th line of p. 26 of the revised manuscript, it may be better to be revised that “… emitted with different energies and start times…”. Please check it.
• In Fig.22 of the revised manuscript, it seems that there are misspellings in “Signal input”. Please check it.
• In the 932^th line of p. 35, it may be better to be revised that “… the value of neutral flux \gamma_0 can be determined by…”. Please check it.

Author Response

After reading the revised article, I think that it has been revised in a quite satisfactory way because the argument has become clearer than that of the previous one. This review report is very interesting because such fundamental and technical review summary and discussions on FCs for present and also future various accelerator technologies are important.

I believe that this paper gives an important step to wider applications in accelerators and other disciplines. I strongly recommend this article to publish in Instruments.

Finally, I point out a few minor revisions to be revised before publication.

Reply: We would like to thank the referee for their positive feedback and satisfaction with the previous modifications. We have addressed the new comments in the revised manuscript and provide a point by point response below.

 

 

• In the 151^th line of p. 6 of the revised manuscript, it seems that the approximation condition may be correct in not 0.2\lesssim Z_t/Z_i \gtrsim 5 but 0.2\lesssim Z_t/Z_i \lesssim 5. Please check it.

Reply: We would like to thank the referee for pointing out the error. The correction has been made in the revised manuscript.

• In the 301^th line of p. 12 of the revised manuscript, it may be better to be revised that “… … E_{bs} is proportional to the incident energy and …”. Please check it.

Reply: We would like to thank the referee. It has now been corrected (added the missing ‘to’) in the revised manuscript.

• In the 696^th line of p. 26 of the revised manuscript, it may be better to be revised that “… emitted with different energies and start times…”. Please check it.

Reply: We would like to thank the referee for the suggestion. The sentence is now modified in the revised manuscript.

• In Fig.22 of the revised manuscript, it seems that there are misspellings in “Signal input”. Please check it.

Reply: We would like to thank the referee for noticing the issue. We have updated the figure in the revised manuscript.

• In the 932^th line of p. 35, it may be better to be revised that “… the value of neutral flux \gamma_0 can be determined by…”. Please check it.

Reply: We would like to thank the referee for the suggestion. The sentence is now rephrased in the revised manuscript for better clarity.