First Proof-of-Concept Prototype of an Additive Manufactured Radio Frequency Quadrupole

Round 1

Reviewer 1 Report

In this paper, the authors shows the first fabrication of an RFQ vane prototype by using the Additive Manufacturing technique.

"Although these first roughness measurements of the proof-of-concept RFQ show that the obtained surface roughness quality is still far from the required Ra=0.4 μm, it is important to keep in mind that these results were obtained without any specific adaptation of the AM technological process to strike for the better surface roughness outputs."

The authors clearly state that the AM process was not optimized for the ultimate needed surface roughness…is this limitation temporary or will never be possible? In which case, what would the options be?

Moreover, how do they plan to re-machine the cooling channels? Or with they be left as rough as they come out of the AM process?

I believe that the authors should add some details in order to explain possible solutions for the target roughness and/or alternative plans.

Best regards.

Author Response

Point 1. "The authors clearly state that the AM process was not optimized for the ultimate needed surface roughness…is this limitation temporary or will never be possible? In which case, what would the options be?"

Answer: Yes, potentially there are several ways how to achieve improvements and that is covered in the text (See enclosed document  L281-286 and L361 - 366). Also, it might be covered in more detail in future work. 

Point 2. "Moreover, how do they plan to re-machine the cooling channels? Or with they be left as rough as they come out of the AM process?"

Answer: This can be addressed with the scope of post-processing activities. At this stage, we are concentration on the most critical outer surfaces (on surfaces where lower Ra are required, this is improved in the text. Please see enclosed document L264-265). However, the raised issue is a future activity.

Point 3. "I believe that the authors should add some details in order to explain possible solutions for the target roughness and/or alternative plans."

Answer: The raised issue is relevant, however, it has been covered in the text (see enclosed document L375-377).

Thanks for your feedback! I hope our input improved the article.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper discusses the feasibility of using a 3D printer to fabricate RF cavities for accelerators. In the field of metal processing, it has become popular to fabricate complex structures by melting metal powders with a laser. The accelerator field is no exception, and manufacturers have been studying this possibility. In this paper, we discuss the RFQ, which is one of the accelerator cavities that requires a particularly high level of fabrication accuracy. To fabricate an actual cavity, it is necessary to test the RF characteristics and vacuum level. Although this paper does not cover this area, it does report the results of prototyping and measuring the machining accuracy and surface roughness of the vain tips, which require a particularly complex shape. The 750 MHz cavity at CERN, which has a very high frequency, is discussed as a sample due to the allowable size of the machine. It seems difficult to fabricate a 750 MHz cavity using this method at this time, but values that are already within the acceptable range for machining accuracy required by the lower frequency range. The point of conception is very interesting and could yield a lot of citations.

The paper as a whole is easy to read and well organized. I don't think any major changes are needed. I would like to suggest some minor points that could be improved.

L38.

Many high-current RFQs accelerate negative ions.

L88

Is the 90% conductivity value at high frequency, or is it at DC?

You mention the limits of the shapes that can be processed using L-PBF, but this part is not clear.

Author Response

Point 1. "Many high-current RFQs accelerate negative ions."

Answer: unclear place corrected by removing "positively" and now L38 looks as follows "..continuous beam of charged particles like protons or heavier ions as they come out of the ion source [1]."

Point 2. "Is the 90% conductivity value at high frequency, or is it at DC?"

Answer: Measurements is done by IACS standard and now text look as follows: "90% IACS" + footnote L94

Point 3. "You mention the limits of the shapes that can be processed using L-PBF, but this part is not clear."

Answer: We took into account the comment and we rephrased the paragraph. See enclosed document L146-157.

Thanks for your feedback! I hope our input improved the article.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors have submitted a manuscript on the use of additive manufacturing applied to rf quadrupoles. The work is in early development stages and the results are very preliminary, not clear if it can be applied in a useful manner. But the authors present this in a straightforward way and do not make unreasonable claims. The quality of the paper is appropriate for the journal. The paper can be published after revision. Only some minor items should be fixed, listed below.

Please add some references to previous work on additive manufacturing for particle accelerators.

There appears to be a heading error on page 6, line 205 "The Materials In order." Please fix.

The term TRUMPF is not defined or referenced. Please add this.

Author Response

Point 1. "Please add some references to previous work on additive manufacturing for particle accelerators."

Answer: in the text are added additional references, please see the enclosed file from L65-70.

Point 2. "There appears to be a heading error on page 6, line 205 "The Materials In order." Please fix."

Answer: we fixed the error (please look at enclosed document L212)

Point 3. "The term TRUMPF is not defined or referenced. Please add this."

Answer: The TRUMPF is a company, therefore we add GmbH to show that (please look at enclosed document L218). I hope that solve this point.

Thanks for your feedback! I hope our input improved the article.

Author Response File: Author Response.docx