Digital Miniature Cathode Ray Magnetometer

Round 1

Reviewer 1 Report

This paper presents the development of a Digital Miniature Cathode Ray Magnetometer in a very didactic manner, accessible to potential users without a specific background in in measurement technology, miniaturization, signal treatment.
The need to measure accurately the local magnetic field exist in many different communities, scientific research, development, high technology industries, … where the final user is not necessarily an expert in the measurement technology. Many techniques already exist, but as quoted in the introduction part of the paper, they all present several drawbacks.
The concept presented here provides spatial resolution accuracy, high dynamic range and absolute measurement and a wide temperature range of operation including cryogenic temperature. The most impressive aspect of this new technology is its versatility and the possibility to tune different prototypes to the needs of various users, e.g. by favoring accuracy (down to 25μT) or dynamic range (expected up to 3T) with a small modification of the system. Although only one prototype was realized to apply to wiggler inspection in light sources, it is easy to perceive that a wider range of applications is at hand.

The English level is very clear and accessible. We recommend to publish the paper as it is.

Author Response

Thank you very much for your comments.

Reviewer 2 Report

Summary

The article starts with an overview of magnetic field measurement methods and their strength and weaknesses. It introduces the space where the discussed novel Digital Miniature Cathode Ray Magnetometer (DMCRM) fit into that space. The second part presents the details of the prototype. The third part presents simulations and measurements of the performance of such a DMCRM prototype optimized for light source undulator mapping. Followed by a description of different improvements of such a device to eventually achieve the stringent requirements of the application mentioned above. Many of these next-generation improvements are work in progress.

General concept comments

Congratulations to the authors for the presented prototype. I recommend this proof-of-concept and the first results from a prototype for publication. From my point of view, in its current form, the article lacks some details, mainly around the technical details of the tested prototype, and shows some minor structural weaknesses with repetitions regarding future developments in the Discussions and the Summary chapters. Specific details are given below. 

Introduction

This section provides a concise "landscape" of magnetometry and provides an excellent framework to understand where the novel technology fits in. Some rough quantitative statements might be added to specify the qualitative statements like "faint fields", "temperature drift" (what scale), or "lack spatial resolution". 

Construction and Materials

This section provides a decent overview of the tested DMCRM prototypes. The figures/pictures in this section, except for Figure 1, would benefit from scales and additional technical details in the caption. Some of the parameters mentioned in this section are not discussed in the "Results" chapter (-50V on the cylinder, results other than 250V, lens vs. direct attachment).

Performance and Optimization

The first part of this section describes the performance of a very specific prototype. I recommend specifying the parameters of this very speific prototype more specific. As mentioned above, it is mentioned that some parameters were tested in a range, but the results are not quantitatively shown here. I recommend expanding on showing quantitative results. More details are given in the specific comments. 

Discussion

This section provides a very compelling discussion of further improvements. I would consider changing the title accordingly. For me, there are too many details in the last part discussing hypothetical signal processing details. I recommend to make the last part of this section more concise. 

Conclusions

The conclusion re-iterates some details more than I would consider necessary. I'd recommend expanding on the test results by potentially stating the achieved key performance parameters again, listing the future improvements but shortening the description, and referring to the Discussions chapter. Keeping the order used in the discussion order makes it easier for the reader to follow. The last paragraph provides an elegant bracket to the introduction closing the paper.

Specific comments

Introduction

49: while NMR is mentioned in the technologies, its strengths and weaknesses are not discussed here. In particular, because you propose MRI mapping, adding a sentence to NMR might be beneficial.  

50: "this", I recommend making clearer that this refers to the novel technology described in this article.

53: first use of CMOS, but defined only on line 82

56: "Executing calculations essential" sounds pretty vague; be more explicit about what it does. 

57: "orientation", I assume this technology only measures two dimensions? Might be worth to be more specific here.

59: "accuracy", the authors mention "accuracy" here, but in the body of the paper, accuracy is not discussed. I recommend adding information about the accuracy of the prototypes achieved.

62: "without the need of calibration". I assume the device needs to be calibrated at zero field ones? Do the authors maybe mean recalibration at other temperatures? 

64: A sentence mentioning that while the described devise is optimized for undulators, there are also other potential applications like the ones mentioned starting in this paragraph.

67: reference [4] doesn't seem to mention DMCRM. I recommend clarifying that the reference only describes the mentioned applications but doesn't mention DMCRM explicitly.

67: "can" -> "could" since, if I understand right, this is purely hypothetical at this point.

Construction and Materials

Figure 2: is the shown electron emitter W or LaBe6?

Figure 2: add scales

123: clarify that the spectrum peaks at 450nm

125-127: To me, this sentence is unclear. Aren't both arguments favoring the version with the lens? In this light, the sentence structure with "while" is unclear to me. Clarifications in which cases no lens is used.

129: around here a discussion about CMOS pixel size might be benefical?

Figure 3: scales in the pictures

Figure 3: what are the types/models of the shown CMOS (I assume commercial?), What's their pixel size? What is the size of b)?

Performance and Optimization

156-159: The transition between these sentences confuses me. I recommend the authors line out first what the prototype discussed in the first part of this section is optimized for and then describe it, followed by results. 

159-166: In the introduction, accuracy is also mentioned. Are there requirements for accuracy? I recommend adding a sentence about accuracy (requirements and, if possible, also what was achieved)

172: I'm a little lost in the discussion of the pixel size. First of all, it would be good for the reader to know what pixel size was used for the prototype. Secondly, here you state that 25uT can be achieved up to 10um, but on the other hand, you have not yet been able to demonstrate that. This should be clarified. 

174: this is not a complete sentence.

174-179: the discussed prototype, what sensor is used, what pixel size, what emitter material?

176: "length" -> "width"?

183: I'm confused here. You state that 250V "meeting the requirements of the targeted application", but doesn't the current prototype fall short by a factor of 5 (as mentioned in line 178?)

189: In the previous chapter, you mentioned that you tested the performance from 200 to 2000V. I recommend presenting these results here, further motivating the choice of 250V. This sentence would benefit from some quantitative argument. 

208: huge space between number and units

Table 1: I recommend stating the simulation values and the measurements, with uncertainties from the measurements (I assume you get that from multiple measurements at the same field, aka translate the stated 1um to the corresponding field sensitivities), separately to demonstrate to the reader how well they agree.

Figure 5: adding a signal from the 400 to 800um probe as a reference be beneficial here?

Figure 5: add scale

Figure 5: to me, it's unclear if all these pixels are saturated. A cross-section (s) with one dimension versus pixel value would be useful for the reader to understand the signals better. It would also help to illustrate the Gaussian character of the signal. 

Discussion

270: to me, it sounds like the very small form factor is an additional challenge the authors might want to consider mentioning here 

283: if the "beam deflection" is mentioned here as a challenge, the authors might consider discussing this topic already earlier in the article.

287: If this is a plan for the future, might the use of "would" instead of "is" be more appropriate? 

334: I assume a FPGA implementation would also greatly benefit the compensation idea mentioned earlier? If that is the case, the authors might consider adding a reference here. 

335-349: this very detailed discussion about the technical implementation seems to be too much detail for hypothetical future work in the context of this article. From my point of view, the point was already clear from the two paragraphs above (I would also consider shortening them). The fact that the authors are planning on using an IPBus in the future doesn't contribute to the topic of this article.

Conclusions

355: I recommend stating again that a 5mm diameter prototype was built and tested in this work. Potentially state the key performance parameters again. 

356: I believe this is not a full sentence.

358-359: I recommend the authors consider moving the statement about a potential custom CMOS to the end of the Discussion chapter. And here, just list the FPGA/DSP and other potential improvements very briefly without much detail since that's discussed in the last chapter. Keeping the same order as in the Discussion chapter would make it easier for the reader to follow.

360-371: to me, it is not completely clear how the fiber bundle here is significantly different from the concepts described in the Discussion section, and hence, the split between Discussion and Conclusion is not completely clear. I recommend having discussions and explanations in the Discussion sections, and here in the conclusion, briefly list all these ideas for future improvement. 

Author Response

Thank you very much for your comments. All the questions are addressed in the attached document and the revised paper.

Author Response File: Author Response.pdf