The DREAM Endstation at the Linac Coherent Light Source

Round 1

Reviewer 1 Report

Li and coauthors reported and outlined the design of a Dynamic Reaction Microscope (DREAM) endstation at the Linac Coherent Light Source (LCLS). The authors conducted simulations of both Coulomb explosion imaging and electron-ion coincidence experiments to showcase the capabilities of the DREAM endstation. Thanks to the pulse properties and high repetition rate (1MHz) of the upgraded LCLS-II, the authors claimed that a wide range of scientific opportunities are enabled, providing unprecedented opportunities to study charge and energy flow in photo-excited systems. With the ability to detect ions and electrons in coincidence, the DREAM endstation offers the science community a powerful new tool to study photoinduced quantum phenomenon. 

The introduction of the motivation, the detailed description of the DREAM design, the plot of the hardware layout, and the presentation of the simulation data are of high quality. The entire manuscript is very well written. 

As a previous LCLS-I user, I believe the entire science community is eagerly looking forward to the full commissioning of the LCLS-II. The DREAM endstation at LCLS-II reported in this manuscript is very likely to yield significant scientific advancements in the near future. 

From what has been presented, I would recommend the publication of this manuscript without hesitation.

Author Response

Dear Sirs and Madams,

First of all, we thank the reviewers for their positive feedback, and their very detailed look into our manuscript. We appreciate the reviewers’ extremely helpful comments and suggestions, which we believe helped us improve the clarity of our manuscript. We have addressed every points of concerns, and to emphasize this in the revised manuscript, we have implemented the following changes in order to better guide the reader through the individual findings and discussions:

General changes:

First Author Xiang Li has been moved through the author list in alphabetical order at his own request. Some minor reorders were implemented for this change. The corresponding author remains the same.

Further proof reading has been done and minor typos and mistakes have been corrected. 

All changes made to the text are marked in red. 

Response to Referee 1 

We thank the reviewer for their positive assessment of the manuscript, and their feedback. We share their enthusiasm about this endstation that we are commissioning for next generation high-repetition rate FEL based multi-particle coincidence spectroscopy.

Response to Referee 2

We thank the reviewer for their kind assessment of the manuscript and their detailed feedback. In the following, we are describing the changes made to the manuscript to implement the suggestions made the reviewer:

1. We thank the reviewer for their detailed reviews, and we modified the text to reflect the proper units and formatting throughout the text. The changes are marked in red.
2. We have adjusted the positions of the figures and also made appropriate adjustments in the text.
3. We have made adjustments in the text to better accommodate the tables.
4. We agree with the reviewer, and we have added more information about the specific points made by the reviewer and also made sure acronyms are introduced correctly. The points address can be found in page 5, lines 137-141 which addresses details and modality of the jet assembly; in page 7 lines 160-162 and lines 167 - 172 which addresses details about the TIXEL detectors; and in lines 173 - 174, which guides the reader about the necessary parameters emphasizing the capability of TIXEL.
5. More information has been added to the text regarding the MHz operation of the KB mirrors on page 2, lines 80-82
6. The information about the readiness for user experiments has been added to the manuscript on page 16, line 357-358.

Reviewer 2 Report

The manuscript entitled “(Design and simulation of)The DREAM Endstation at the Linac Coherent Light Source” by Li et al. presents a new endstation for electron and ion spectroscopy studies at LCLS-II. The paper summarizes the design of the endstation and discusses some simulations of its performance. I recommend publication of the manuscript in Applied Sciences. However, some (mainly minor) points should be addressed before:

11.   Please check the wording and style throughout the manuscript. E.g. instead of “um” please write “µm” or the two sentences in the middle of page 5 “The basic idea…  The idea here is…” There are many more examples. Also there are some labelling that did not work, such as on page 10 a reference to “[??]$ and on page 11 to “Fig. ??”.

22.    In general, I recommend to first reference to a figure that shows some details and describe those afterwards. In sections 2.1, 2.2, 2.3 this is done the opposite way, where the reference to the corresponding figure is given at the end of the paragraph.

33.    In this context, tables 2 and 3 are not referenced at all in the text. Especially table 3 summarizing all technical details of the endstation should be introduced in the main text.

44.    I am missing some details in the description of the endstation parts. In particular: (1) details of the jets and (2) detector details. For (1), what kind of jets and nozzles are planned/used? Is this versatile / decided by the users? Can users bring their own environments? For (2), although this detector is rather prototypical, please provide more details. For instance, TOT and TOA are not defined (I assume TOT means “time over threshold”, but not every reader knows such abbreviations). Also in the text a rate of 1 MHz is given, table 2 says “5kfps” for “Full matrix readout”. This should be specified, and maybe compared to existing MHz FEL detectors (e.g. at European XFEL which make use of the pulse train structure of the XFEL).

55.    Are there any issues with MHz operation for the optical components? At European XFEL, first MHz experiment showed not only influences on samples but also on optical components such as heat load on monochromators (see e.g. doi:10.1364/OE.451110). Please provide details.

66.    Maybe most important, is the endstation already operational? Please give an estimate for its time frame, e.g. user operations.

Author Response

Dear Sirs and Madams,

First of all, we thank the reviewers for their positive feedback, and their very detailed look into our manuscript. We appreciate the reviewers’ extremely helpful comments and suggestions, which we believe helped us improve the clarity of our manuscript. We have addressed every points of concerns, and to emphasize this in the revised manuscript, we have implemented the following changes in order to better guide the reader through the individual findings and discussions:

General changes:

First Author Xiang Li has been moved through the author list in alphabetical order at his own request. Some minor reorders were implemented for this change. The corresponding author remains the same.

Further proof reading has been done and minor typos and mistakes have been corrected. 

All changes made to the text are marked in red. 

Response to Referee 1 

We thank the reviewer for their positive assessment of the manuscript, and their feedback. We share their enthusiasm about this endstation that we are commissioning for next generation high-repetition rate FEL based multi-particle coincidence spectroscopy.

Response to Referee 2

We thank the reviewer for their kind assessment of the manuscript and their detailed feedback. In the following, we are describing the changes made to the manuscript to implement the suggestions made the reviewer:

1. We thank the reviewer for their detailed reviews, and we modified the text to reflect the proper units and formatting throughout the text. The changes are marked in red.
2. We have adjusted the positions of the figures and also made appropriate adjustments in the text.
3. We have made adjustments in the text to better accommodate the tables.
4. We agree with the reviewer, and we have added more information about the specific points made by the reviewer and also made sure acronyms are introduced correctly. The points address can be found in page 5, lines 137-141 which addresses details and modality of the jet assembly; in page 7 lines 160-162 and lines 167 - 172 which addresses details about the TIXEL detectors; and in lines 173 - 174, which guides the reader about the necessary parameters emphasizing the capability of TIXEL.
5. More information has been added to the text regarding the MHz operation of the KB mirrors on page 2, lines 80-82
6. The information about the readiness for user experiments has been added to the manuscript on page 16, line 357-358.