Cryogenic Facility for Prototyping ET-LF Payloads Using Conductive Cooling

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

The reviewer believes that in this work the authors have successfully solved a problem of extreme complexity, thanks to their many years of experience working with the Virgo and KAGRA gravitational-wave interferometers. Most of them are co-authors of the project [2] \\

 Without a doubt, their manuscript deserves to be published in the Galaxies journal. 

The reviewer has, however, some minor comments that it would be desirable to correct:

1. the article contains figure 3 (cryogenic payload), but there is no reference to it in the text .                                                                                                        

2. figure 4 (close-up view) is unclear, especially in its right part, I ask that this part be corrected or replaced.

Author Response

Thank you very much for taking the time to review this manuscript.  Please find the detailed response below:

1. the article contains figure 3 (cryogenic payload), but there is no reference to it in the text .                                                                                                        

The payload, depicted in Figure 6 (Figure 3 of the first version of the manuscript), is described in detail from Line 156 ; we added the names of the main components on the Figure. 

2. figure 4 (close-up view) is unclear, especially in its right part, I ask that this part be corrected or replaced.

Thank you for the hint, actually the Figure 4 was not clear so we decided to divide it in two different figures (Figure 7 and Figure 8). We added clearer captions on the Figures and a better explaination in the text. Line 180-201

Reviewer 2 Report

Comments and Suggestions for Authors

The paper shows a description of a prototype for an experiment to test the cooling capabilities for the mirror of the Einstein Telescope, in a simplified version. The paper is promising but it seems to be a little short as some of the explanations are not complete, which makes the reader guess the real content. Attached is a file with the regions that needs to be improved, the regions are highlighted with some comments. The paper could be published with all the suggested improvements.

Comments for author File: Comments.pdf

Author Response

Thank you very much for taking the time to review this manuscript.  
Regarding the highlighted sentences without specific comments, we have done our best to rephrase them.

Detailed explanations for all other comments are provided below:

Line 5
This fact is not mentioned in the text.

We rephrased the sentence and mentioned the high quality factor in Line 37 and Line 191-194.

Line 6-10
Rephrase it!

Thank you for pointing this out. We rephrased the abstract.

Figure 1
Indicate the refrigeration line.

Thanks for the hint. We added labels in the Figure 1 and added Figure 2 for better understanding of the infrastructure.

Line 40-41
A figure in be great.

Thanks for the suggestion. A better view of the Pulse Tubes can be seen in Figure 4 and their location is indicated also in Figure 1 and Figure 3.

Line 59
More explanation is needed!

We rephrased Line 59-61, now Lines 69-74, in order to explain the relevance of soft heat links to damp vibrations.

Figure 2
It will be good showing the suspension of the cooling bar.

Thanks for the suggestion. We added Figure 4 for better view of the suspension.

Line 74-77
Why different temperatures?

Thank you for your question. We pointed the expected temperatures at the connection of the Pulse Tube. Since the First stage connection to the shield of the refrigeration line will have a temperature of 30K, the reference thermal conductivity value has been indicated at 30K. The second stage connection will be around 10K, so the reference thermal conductivity value has been indicated at 10K. Line 83-88

Line 85
A reference will be good.

If this comment is related to the Rigid Multi Layer, then, this solution was conceived by us. Hence, there are no references yet. 

Line 94-96
In it shown in figure 1?

We rephrased Line 94-96, now 112-118. We explained the mounting and maintenance procedure based on the horizontal division of the system. Moreover, we added Figure 5 for better visualization.

 

Line 112
In this temperature for the payload or for the ITS?
If it is for the ITS, why this temperature is higher than the temperature of the OTS?

The 120K is the temperature of the payload during its cooling. That is not a steady-state temperature but a transient one. The payload will be cooled to its target temperature starting from room temperature and the two heat transfer method are conduction and radiation. From room temperature to around 120K, the radiation contribution is the relevant one, from 120K to the target temperature the radiation becomes ineffective and the conduction will be the predominant heat transfer method. We tried to summarize this concept in Lines 141-144.

Figure 3
Is that the sapphire rod?
what are these?

We added a more detailed caption and labels on the Figure 3 (now Figure 6) to distinguish better all the components of the payload.

Line 119
Where is the sapphire rod?

Now the sapphire rod is highlighted in Figure 6.

Line 155-157
Rephrase it!

We rephrased the sentences in Lines 191-195.

Figure 4 
What is a and b? Where are the two ribbons connected to the two sapphire blocks?

Thank you for the hint, actually the Figure 4 was not clear so we decided to divide it in two different figures (Figure 7 and Figure 8). We added clearer captions on the Figures and a better explaination in the text. Line 180-201.

 

Line 184
Simulations made how?
Show the results.

The simulations will be part of a more technical review of the project now in preparation. However, some highlights have been added along with Figures showing the results (Figure 9, 10, 11, 12). Chapter 4.

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Prof. Marco Ricci and all authors,

 

Thank you very much for your interesting and energetic research. This paper described about the design to test cryogenic mechanical suspensions for the ET-LF payloads. This work is very important foreseen for the Einstein Telescope. With the main revising, mainly the additional explanation, this paper should be accepted.

 

There are several comments, questions and requests.

 

Line15:

Is ETIC the initials of the “Einstein Telescope Infrastructure Consortium”? If it is correct, could you add it to the Abbreviations (line 231)

 

Line 18:

You wrote “its timeline is December 2025”. Could you tell us more detail about the timeline? The timeline of the design of the prototype, construct the manufacture of the prototype or experience of the cooling down?

 

Line 23:

Please add the KAGRA cryogenic system paper reference after [1]?

https://iopscience.iop.org/article/10.1088/1361-6382/abe9f3

 

Line 29:

It may be written in the reference [2] in detail, could you add the brief explanation about the ET-LF suspensions?

 

Line 32:

There are the description of the “technical noise injected by the cryogenics system”. What is the main technical noise? Vibration, sound, vacuum pressure and/or magnetic field? I think you need to add more description of the technical noise. One of the evaluation of environmental noise in KAGRA cryogenic system can be seen in 

https://iopscience.iop.org/article/10.1088/1361-6382/ac7cb5

 

Line 34:

Please add the reference of the KAGRA experience of the vibration from the heat link.

https://www.sciencedirect.com/science/article/abs/pii/S0011227521000382

 

Line 37:

This is just my interest, could you tell me the mean of “75” of the cryostat C75?

 

Line 44:

About the Figure 1. Could you add more explanation to the sectional view of the Figure .1? We cannot see the volume of this system, name of each component, where is the two refrigeration lines, cryostat C75 and cryogenic payload? Where are the PT420 and PT425? 

 

Line 55:

What the difference of the PT420 and PT425? You described the reason why you choose total for cryocooles in your paper, but if possible, could you add more detail description of the reason?

 

Line 57:

Do you have a spectrum of the vibration (1.4 Hz and its harmonics)?

 

Line 59-61:

You described to test the effect of the cryosystem to payload. Do you have some idea to evaluate this effect? Using cryogenic acceleration system or cryogenic monitor of TM, MN and platform?

 

Line 66:

Same as Figure 1., could you add more explanation to the sectional view?

 

Line 80:

Do you have a goal of the vacuum level in this system? To achieve this, is this design satisfied?

 

Line 81 – 82:

“for optical levers, thermometers, stiffeners etc…”, This description is too insufficient explanation. Will optical levers monitor the angular motion of TM or more, will optical levers set on the ground or cryostat? Do you have a plan to use other sensors, such as photo sensor? What type of the thermometers will you use? What is the stiffeners? How to evacuate this cryostat?

 

Line 83 and 87:

You described the design of the dodecagonal shape in outer and inner thermal shields, Could you let us the reason why you choose this design?

 

Line 117:

I cannot find the description about the Figure 3. in the main contents. If you want to add the Figure 3., please add the description to main contents. And in the caption, 1. Section of -> Sectional view 2. they reach the “Actuation” Cage (AC)…

 

L126:

Could you let me know the motivation and difference of the “initial test” and different test? 

 

L 129:

This is my opinion, but to achieve the 20 K, the monitoring system of mirror surface and mirror height would be important. Do you have a plan to do this?

 

L 149 – 150;

I cannot catch up the point from this description. Could you add more explanation what is the Figure 4. And what do you want to say from Figure 4.?

 

L 183:

Could you explain more about the method of the simulation? Mainly by the theoretical calculation or some special simulation software?

Also, could you let us know the goal of those simulation? Check of the following four contents? If so, you need more description of the results of the simulation

 

L206:

If possible, could you write the future plan and/or schedule of this project? Construction of the infrastructure soon or need more investigation of the design or start cooling down as soon as possible?

 

Comments for author File: Comments.pdf

Author Response

Thank you very much for taking the time to review this manuscript.  Please find the detailed response below:

Line15:

Is ETIC the initials of the “Einstein Telescope Infrastructure Consortium”? If it is correct, could you add it to the Abbreviations (line 231)

 

Thank you for pointing it out. We inserted ETIC in the abbreviations and stressed it in the text.

 

Line 18:

You wrote “its timeline is December 2025”. Could you tell us more detail about the timeline? The timeline of the design of the prototype, construct the manufacture of the prototype or experience of the cooling down?

 

We updated the timeline of the project with the delivery deadline (December 2025) and subsequent assembly and test (2026) in Line 18.

 

Line 23:

Please add the KAGRA cryogenic system paper reference after [1]?

https://iopscience.iop.org/article/10.1088/1361-6382/abe9f3

 

Thank you for the suggestion, we added the reference for a better and more complete understanding of the topic.

 

Line 29:

It may be written in the reference [2] in detail, could you add the brief explanation about the ET-LF suspensions?

We added a brief explaination of the ET-LF suspension and cooling scenario. Line 29-37.

 

Line 32:

There are the description of the “technical noise injected by the cryogenics system”. What is the main technical noise? Vibration, sound, vacuum pressure and/or magnetic field? I think you need to add more description of the technical noise. One of the evaluation of environmental noise in KAGRA cryogenic system can be seen in 

https://iopscience.iop.org/article/10.1088/1361-6382/ac7cb5

 

Thanks for the hint, the technical noise we considered in the first version of the manuscript was the one coming from PTs. Now we have remarked it in the new version (Line 39-43) and we have cited the suggested reference.

 

Line 34:

Please add the reference of the KAGRA experience of the vibration from the heat link.

https://www.sciencedirect.com/science/article/abs/pii/S0011227521000382

 

Thanks, we added the reference.

 

Line 37:

This is just my interest, could you tell me the mean of “75” of the cryostat C75?

Thank you for your interest, 75 stands for the size of our cryostat which, in principle, was the 75% of the envisaged size of ET-LF cryostat. See Line 52.

 

Line 44:

About the Figure 1. Could you add more explanation to the sectional view of the Figure .1? We cannot see the volume of this system, name of each component, where is the two refrigeration lines, cryostat C75 and cryogenic payload? Where are the PT420 and PT425? 

 

We added a better view of the infrastructure with the description of all the components. Figure 1 and Figure 2.

 

Line 55:

What the difference of the PT420 and PT425? You described the reason why you choose total for cryocooles in your paper, but if possible, could you add more detail description of the reason?

 

We added the reference performance of the PT chosen in the system. We first bought the PT420 and later upgraded to the PT425 when it was released because it offered more power.  Then we decided to use the PT425 for the cooling of the Payload. Line 62-66

 

Line 57:

Do you have a spectrum of the vibration (1.4 Hz and its harmonics)?

No, at the moment we still don't have the spectrum of vibrations of the PTs in our system. However, from the experience with other PTs of Cryomech, we know the frequency of the PT with the relevance of the harmonics. 

 

Line 59-61:

You described to test the effect of the cryosystem to payload. Do you have some idea to evaluate this effect? Using cryogenic acceleration system or cryogenic monitor of TM, MN and platform?

We will use cryogenic accelemeters and geophones (now under development) Line 90-92.

 

Line 66:

Same as Figure 1., could you add more explanation to the sectional view?

The sectional view of the refrigeration line has been updated with the description of the components (Figure 3). Figure 4 has been added with a view of the suspension mechanism of the shield and cooling bar.

 

Line 80:

Do you have a goal of the vacuum level in this system? To achieve this, is this design satisfied?

At the moment we don't have a clear idea of the vacuum level we will reach. First tests on the refrigeration lines will be performed before the complete assembly of the system. At that point we will have an estimation of the time and vacuum level of these components, this will help us in a better comprehension. The general idea is to have a pressure better than 10^-5 mbar at room temperature. 

 

Line 81 – 82:

“for optical levers, thermometers, stiffeners etc…”, This description is too insufficient explanation. Will optical levers monitor the angular motion of TM or more, will optical levers set on the ground or cryostat? Do you have a plan to use other sensors, such as photo sensor? What type of the thermometers will you use? What is the stiffeners? How to evacuate this cryostat?

 

We added a better description of all the sensors we will use in the system (Line 99 - Line 123 - Line 150). The pumps has been described in Line 119-122.

 

Line 83 and 87:

You described the design of the dodecagonal shape in outer and inner thermal shields, Could you let us the reason why you choose this design?

 

We explained the motivation behind the decision in Line 146 and in Figure 2.

 

Line 117:

I cannot find the description about the Figure 3. in the main contents. If you want to add the Figure 3., please add the description to main contents. And in the caption, 1. Section of -> Sectional view 2. they reach the “Actuation” Cage (AC)…

 

The payload, depicted in Figure 6 (Figure 3 of the first version of the manuscript), is described in detail from Line 156 ; we added the names of the main components on the Figure. 

 

L126:

Could you let me know the motivation and difference of the “initial test” and different test? 

 

Line 165. We rephrased the sentence to better explain the following: initially, we will use a dummy aluminum mirror, later on we will consider to replace it with a real crystalline mirror. 

 

L 129:

This is my opinion, but to achieve the 20 K, the monitoring system of mirror surface and mirror height would be important. Do you have a plan to do this?

Thanks for the interest. The aim of the project is to validate the cooling through PTs and soft heat links. The target temperature is 20K, so we designed the heat links number and dimension in order to obtain such a temperature. The system will also consider a realistic heat input on the mirror which mimics the input from the laser, we will obtain such a heat input by using heaters on the mirror. At regime (with the heat input) the mirror temperature should be around 20K. 

 

L 149 – 150;

I cannot catch up the point from this description. Could you add more explanation what is the Figure 4. And what do you want to say from Figure 4.?

 

Thank you for the hint, actually the Figure 4 was not clear so we decided to divide it in two different figures (Figure 7 and Figure 8). We added clearer captions on the Figures and a better explaination in the text. Line 180-201.

 

L 183:

Could you explain more about the method of the simulation? Mainly by the theoretical calculation or some special simulation software?

Also, could you let us know the goal of those simulation? Check of the following four contents? If so, you need more description of the results of the simulation

 

The simulations will be part of a more technical review of the project now in preparation. However, some highlights have been added along with Figures showing the results (Figure 9, 10, 11, 12). Chapter 4.

 

L206:

If possible, could you write the future plan and/or schedule of this project? Construction of the infrastructure soon or need more investigation of the design or start cooling down as soon as possible?

 

We added the timeline of the project in Line 17-20. The design has been frozen with the company and the delivery is planned before December 2025. The first cooling of the setup will not be done before 2026. 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The paper is much better now. There is, at least, one typping probem in line 139: foil-based heat links.Its average target temperature is 15K.  Now the paper can be published, making this correction. il-based heat links.Its average target temperature is 15 Kfoil-based heat links.Its average target temperature is 15 K