A Systematic Investigation of Beam Losses and Position-Reconstruction Techniques Measured with a Novel oBLM at CLEAR^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript: instruments-3470025

Title
A systematic investigation of beam losses and position reconstruction techniques measured with a novel oBLM at CLEAR

General comment
The manuscript is interesting, rather clearly written apart from the lack of some details that would improve its readability for users not well acquainted with electron accelerators and their operational concepts. I suggest to take care of this aspect in order to improve the understanding by the foreseen audience of readers.
I found that an equation is wrong and requires correction.

I recommends acceptance for publication, with minor changes as specified below.



Lines 124-130
I would recommend to extend this paragraph, providing enough details to readers not acquainted with the CLEAR accelerator features and operations: bunches, train charges,... I also suggest to specify the number of electrons/bunch, in addition to the 0.3nC charge, that provides an immediate reference number avoiding a mental calculation.
In addition, the issue of standard deviation at line 127 should be better described.

Equation at line 165-166
The same symbol L is wrongly used for two different quantities: (i) the coordinate along the fiber (say e.g. X), and (ii) the fiber length L. Moreover, the "+" sign in +L/2 perhaps should be "-", even though this depends on the choice of the coordinate direction. Please correct and clarify in the text.

Line 176
Train length? I guess this deserves a clearer definition/explanation. Please clarify, possibly with a typical example of train, bunches, durations, time spacing.

Figs.6 and 7
How come that the time scales (x-axes) are so much different from figs.4 and 5? Please explain.

Author Response

Please see the attachment. Thank you very much for your comments!

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents simulations and experimental results of a new oBLM system at the CLEAR facility at CERN. A previous “prototype setup” was already installed at this facility, and the results of those studies have been published in another journal. Monte-Carlo simulations of particle losses were run using the FLUKA code, and the upstream and downstream signals resulting from the simulated particle loss were compared. Experimental results are presented in which four screens located at various positions along the beam line were inserted into the beam to induce particle losses. The loss-position reconstruction technique is described, including the difference between the upstream and downstream signals, as well as various conversion methods. According to the authors, this is the first experiment testing both SiPMs and PMTs at the same facility, which allows a direct comparison of the two detector types, although the resolution of the system was found not to be the determining factor for the choice of detector in this case. Finally, the GUI developed for use at CLEAR with the oBLM system is presented.

This paper fits within the scope of the journal and builds upon previous work to provide further interesting results on oBLM systems at CLEAR. Overall, the paper is well structured, though the studies presented here could be more clearly placed in context in order to clarify what the novel aspects are. Furthermore, clarity could be improved in a number of places. Detailed comments are provided below.

 

General comments

1. The authors could do a better job placing this work in context of previous studies. Two previous works are referenced regarding a “prototype setup” at CLEAR, but the results of these studies are not mentioned in this paper. It is therefore not evident what the main differences are between the “prototype setup” previously published and the “novel installation” presented here. What, in particular, is “novel” about the current installation? Did previous results influence the design decisions? How does this setup compare to installations at other facilities? By discussing these issues, the authors could help the reader understand the context of their studies and any novel aspects.

2. In a number of places, qualitative comparisons are given, using words such as “relatively small”, “slightly lower”, “moderately”. These types of comparisons are vague and open to interpretation. More precise, ideally quantitative, comparisons would improve this paper.

 

Specific comments

1. The study’s key findings/results are missing from the abstract.

2. The first sentence of the introduction should contain references to other oBLM systems.

3. The introduction should mention advantages over other BLM systems.

4. Line 31: Does “these” refer to PMTs? This is not clear.

5. Line 35: A “novel installation” is mentioned. What is novel about it? How is it different from the previous setup? Is it novel compared to the previous setup at CLEAR or compared to oBLMs at other facilities?

6. Sec. 2.2: Suggest including a schematic of the setup. It is not clear why 130 m length is required for a 40 m long linac. Is most of the fibre length used to connect to the readout electronics in the gallery above? How far away is the gallery?

7. Lines 66-67: Should state that the optical fibre is located vertically above the beam line (assuming I’ve understood correctly).

8. Line 78: Presumably these dimensions are consistent with those of the CLEAR beam pipe, but this should be explicitly stated. Is 2 cm the inner or outer radius?

9. Line 81: Why were 2.5 million primary electrons chosen? Was a convergence study run? What does “numerous” mean? At least stating the order of magnitude would be helpful.

10. Line 85: How is the range -1 to 3 m determined? From Fig. 1 it looks like the intensity at -1 m is a lot less than the intensity at +3 m. It would be better to quantify this, e.g. with a 5 sigma range.

11. Line 86: How many particles hit the fibre beyond 16 m?

12. Line 89: Does “created” mean “secondary” particles?

13. Fig. 2: Should clarify that the x-axis is the position of the fibre hit. How is this position reconstructed for the upstream and downstream signals? Which errors are included?

14. Lines 98-102: Should mention what determines whether photons are emitted after a hit. Should the upstream be “5 times less” or “5% less”? What order of magnitude is meant by “multiple photons”?

15. Line 107: Should state why the upstream signal provides a “more accurate reconstruction”.

16. Line 119: What material are the screens made of?

17. Lines 127-130: What are the sources of uncertainty? Is the uncertainty mentioned in line 128 the “standard deviation” mentioned on the line above, but just when considering 20 shots? The statement “even single shot measurements can give valuable information” is unclear. Is the point that 20% uncertainty sufficient for certain applications? If so, which applications?

18. Line 165: This equation is not at all clear. How is L defined? What corresponds to L = 0? Why does L appear on both sides of the equation?

19. Line 166: It seems difficult to believe that the length of the fibre is only known to within 1.3 m. Surely it can be measured to much better precision.

20. Lines 176 to 178: This is not formulated clearly. Why should the maximum of the waveform correspond to triggering at the start of the train?

21. Line 209: What is meant by “relatively small”?

22. Fig. 4 and 5: It looks like the ratio of downstream to upstream signals is about 5 to 6; however, in Fig. 2 it is about 10. Why is this?

23. Line 253: “slightly lower noise levels” should be quantified.

24. Line 256: It should be stated whether this problem is specific to the SiPMs used here or is a general problem for SiPMs.

25. Line 262: Should clarify these are “longitudinal positions”.

26. Line 263: Should state what the 20 measured waveforms correspond to.

27. Line 268: Is the difference between the origins due to installation tolerances?

28. Fig. 8: Why is the uncertainty for the point around 30 m so high compared to the others? The black line does not look like a very good fit. What is the value of a and its uncertainty?

29. Line 279: It is not clear what rms deviation is being referred to here. The rest of this paragraph is also not very clearly formulated.

30. “Constant fraction discrimination” instead of “constant fraction discriminator”, as originally introduced, frequently appears in the text.

31. Line 314: Why are results shown with a threshold of 15 mV if 100 mV gives much better results?

32. Line 319: What is the applied voltage?

33. Line 345: What is meant by “significantly” and “moderately”? Can these be quantified?

34. CFD is missing from the list of abbreviations.

Comments on the Quality of English Language

Although the English language is generally understandable, there are a number of grammatical errors and typos that need fixing. Some examples I noticed:

• ‘allow for’ should be ‘allow’ or ‘enable’ (lines 1 & 40)

• ‘allow to + verb’ is frequently used

• ‘analyses methods’ should be ‘analysis methods’ (line 42)

• misspelling of ‘target’ (Fig. 2 caption)

• ‘few’ rather than ‘a few’ (line 85)

• ‘behind of’ (line 86)

• ‘derivative’ should be plural (line 191)

• ‘lower rise time’ should be ‘shorter rise time’ (line 317)

• ‘restraints’ should be ‘constraints’ (line 357)

• ‘later’ should be ‘latter’ (line 369)

Author Response

Please see the attachment. Thank you very much for your extensive review!

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have provided thorough responses to all comments and have made substantial additions and edits to their manuscript based on these comments. In responding to one of the comments they were able to self-identify a mistake in the parameters used for a simulation and have corrected this. I just have some outstanding comments related to Sec 4.4 and Fig. 10, which ought to be addressed prior to publication.

1. The method used for the fit, e.g. least squares, should be explicitly stated in the text. Are the uncertainties on the reconstructed positions taken into account when fitting?
2. The authors mention in their comments that "the fit would seemingly be better if the slope were slightly lower". This does indeed seem to be true for the example shown here, even when only considering the first two screens. Is this generally the case or just for this example? Does it apply when considering both upstream and downstream signals separately? I feel this general issue of the slope deserves some more discussion.
3. I would suggest adding the uncertainty of the fit offset to Fig. 10. This could be displayed as a shaded area or alternatively as error bars at the ends, for example.

Finally, it is not clear how to access the data using the information in line 480.

Comments on the Quality of English Language

Just some minor comments related to the recent additions:

1. Comma in line 341 should be semicolon
2. 'allow to' in line 345 is not grammatically correct

Author Response

Please see the attachment.

Author Response File: Author Response.pdf