From Repeatability to Self-Organization of Guided Streamers Propagating in a Jet of Cold Plasma
Round 1
Reviewer 1 Report
In the manuscript entitled “From repeatability to self-organization of guided streamers propagating in a jet of cold plasma”, the authors describe atmospheric pressure plasma jet device so called CHEREL. Under given conditions the self-organized streamers were occurred. The manuscript is very well written with a many information. Author performed electrical measurement which supported the ICCD camera imaging. It is a pity that the authors did not have available the streak camera with a temporal resolution that they mention in chapter 2.2.2, but the results are sufficient even with the Andor ICCD camera. The results are clearly described and the essence of self-organization is also explained.
The manuscript is novel and the topic of research is highly relevant, but minor changes in the manuscript are necessary:
1. In chapter 3.2.2, you also present the results from optical emission spectroscopy, which suitably complement the diagnosis of the discharge. In chapter 2.2 Diagnostics, however, you do not mention the spectrometer. Complete the technical data about the used spectrometer.
2. In chapter 2.1, you describe the CHEREL device used, where the inner and outer diameter of the capillary is indicated. What is the inner and outer diameter of the inserted hollow electrode? What material is the electrode made of?
3. Line 123: …capillary and polarized to the…
It would be better to write: …capillary and connected to the…
4. Line 126: replace the word “polarized” with e.g. supplied.
After these minor changes, I recommend accepting the article.
Author Response
Dear referee, thank you for your sharp reviewing and for having appreciated this research work. We have carefully addressed your concerns and made the necessary revisions to improve the clarity and rigor of the work."
Comment #1: In chapter 3.2.2, you also present the results from optical emission spectroscopy, which suitably complement the diagnosis of the discharge. In chapter 2.2 Diagnostics, however, you do not mention the spectrometer. Complete the technical data about the used spectrometer.
Answer #1: Thank you for this comment. The following paragraph has been added at the end of section 2.2.2.:
Optical emission spectroscopy is achieved to identify the radiative species from plasma. The spectrometer (SR-750-B1-R model from Andor company) operates in the Czerny Turner configuration, with a 750 mm focal length while diffraction is achieved with a 1200 grooves.mm−1 grating in the visible range. It is equipped with the same camera as the one used to achieve fast ICCD imaging.
Comment #2 : In chapter 2.1, you describe the CHEREL device used, where the inner and outer diameter of the capillary is indicated. What is the inner and outer diameter of the inserted hollow electrode? What material is the electrode made of?
Answer #2 : This information can indeed be added to the first paragraph of section 2.1. Please find the new version of paragraph as follows:
In this work, guided streamers are generated by a plasma device corresponding to a Capillary with inner Hollow Electrode and outer Ring ELectrode (CHEREL). The capillary, in quartz material, is 150 mm in length and has inner and outer diameters of 2 mm and 4 mm respectively. The inner hollow electrode (copper material, din = 1 mm, dout = 2 mm, length = 50 mm) is coaxially centered in the capillary and connected to the high voltage while the outer ring (aluminum material, din = 2 mm, dout = 4 mm, length = 10 mm) is grounded, as indicated in Figure 1a.
Comment #3 : Line 123: …capillary and polarized to the… It would be better to write: …capillary and connected to the…
Answer #3 : Indeed, this verb is more appropriate. Thank you!
Comment #4 : Line 126: replace the word “polarized” with e.g. supplied.
Answer #4 : Thank you for this remark.
Reviewer 2 Report
The paper is a complete characterization of a helium plasma jet impinging on a metalic mesh (MM) electrode placed in series with a grounded metallic plate (MP).
The authors are interested in investigating the behavior of guided streamers under three different target configurations, i.e., MM (floating potential), MP (grounded) and MM-MP.
Using systematic and well designed electrical (different voltage/current signals are measured) and optical methods (OES, ICCD, ...) they are able to distinguish repeatable streamers from self-organized streamers with varying order of complexity depending on the operating conditions of the plasma source. Allthough the former has been widely reported in the literature, much fewer studies have been focused on the latter phenomenon, which is particularly interesting to consider in various plasma-based applications.
The paper is well organised, English is clear, and the results are systematically presented using nice illustrations, which are supported by detailed discussions.
Therefore, the paper is recommended for publication.
Author Response
Dear referee, thank you for your global appreciation which rewards a long research work. We particularly appreciate your sensitiveness to our methodological approach.
Reviewer 3 Report
This paper deals with the behavior of a helium plasma jet at atmospheric pressure in a very specific configuration (jet in front of a floating metallic target followed by a grounded metallic target). The experimental setup is well thought out, the diagnostics are appropriate and the results well analyzed. However, although interesting as such for its singular aspect of highlighting a self-organization of streamers, the interest for the community is quite limited insofar as these observations concern a domain of extremely restricted parameters in an atypical experimental setup. Reading the manuscript is tedious. It has characteristics closer to a PhD thesis manuscript than to a scientific paper. The text is far too long and too detailed. There are way too many figures. The notations are complex, too numerous and sometimes inappropriate. The reader easily loses track of what is being presented. The essential points are drowned in the details. In the interest of the authors, this paper deserves to be completely reworked by favoring a much more synthetic presentation highlighting the essential points. Its length must be divided at least by factor two.
On the other hand, at no time do the authors justify the interest of their research from both a fundamental and an application point of view. What prompted them to develop such an experimental configuration? For what purpose? This would make it possible to place their work in a much more general context and would reinforce the interest of their results.
Considering all of these remarks, it is obvious that the authors must carry out a major revision before resubmitting their manuscript.
Author Response
Dear referee, thank you for your suggestions to improve the quality of this manuscript. We have endeavored to respond to the various points you have raised, although we have wished to retain certain elements of our editorial line. Yours sincerely,
The authors.
Comment #1 : However, although interesting as such for its singular aspect of highlighting a self-organization of streamers, the interest for the community is quite limited insofar as these observations concern a domain of extremely restricted parameters in an atypical experimental setup.
Answer #1 : Beyond the singular/exotic aspect of the experimental setup, it is here the phenomenon of streamers self-organization that it is important and that has not yet been clearly reported in the literature. As you point out, the emergence of self-organized phenomena often requires very specific conditions. We believe that there are strong and interesting spin-offs for applied research and your comment provides a direct bridge to our applied activities in medicine. Consequently, an outlook has been added at the end of conclusion (See answer to your comment #5, below).
Comment #2 : Reading the manuscript is tedious. It has characteristics closer to a PhD thesis manuscript than to a scientific paper. The text is far too long and too detailed. There are way too many figures.
Answer #2 : Although the clarity of the manuscript has been appreciated by the other referees, we also understand that this format may seem "heavy" for others. When we started writing this article, a short format was initially envisaged. Nevertheless, considering the very particular character of the studied phenomenon (self-organization of streamers), it appeared very quickly that it was necessary to analyze it as finely as possible so that no doubt could emerge as to the reliability of the observed phenomena. We could have been confronted with methodological shortcomings such as optical/electrical artefacts which would have invalidated the physical phenomenon and thus the quality of this work. Therefore, we must assume this editorial line to prevent any criticism on lack of scientific rigor. Moreover, the figures are quite explicit to allow a reader in a hurry (or very familiar with the subject) to get a concrete idea of the article.
Comment #3 : The notations are complex, too numerous and sometimes inappropriate. The reader easily loses track of what is being presented. The essential points are drowned in the details.
Answer #3 : Most of the notations rely on the use of Greek letters that are frequently used in the literature. In addition, some of the notations in our article have already been used in papers we have published before, without any particular problem.
Comment #4 : In the interest of the authors, this paper deserves to be completely reworked by favoring a much more synthetic presentation highlighting the essential points. Its length must be divided at least by factor two.
Answer #4 : Reducing this manuscript by a factor of 2 would be detrimental to the rigor of the work done and would erase the subtleties that we wished to highlight. Once again, we must protect the scientific rigor of this work.
Comment #5 : On the other hand, at no time do the authors justify the interest of their research from both a fundamental and an application point of view. What prompted them to develop such an experimental configuration? For what purpose? This would make it possible to place their work in a much more general context and would reinforce the interest of their results. Considering all of these remarks, it is obvious that the authors must carry out a major revision before resubmitting their manuscript.
Answer #5 : Since our study deals with a fundamental research question, we considered that applied research justifications was not a mandatory, as it is often the case for published papers of fundamental research. However, we understand your point of view and the importance to give a context or at least a pragmatic opening to this article. We have therefore completed the conclusion by adding an “outlook paragraph” directly related to our applications in medicine.
In outlook, it is important to underline that this experimental study can have interesting spinoffs for applied research, particularly regarding the engineering of plasma medical devices. For example, in one of our previous papers, we developed a transferred plasma catheter that allows endoscopic treatment of the biliary tree of porcine models [37]. This type of catheter, supplied by helium and powered by high voltage pulses, has a floating electrode (long metallic wire) which endoscopically transfers cold plasma to the area to be treated (human tissue, cells, ...). An obvious parallel can be made by considering that this floating electrode and this region correspond to the MM and MP electrodes respectively. Therefore, this means that the transferred plasma catheter could be used in a modality favoring the self-organization of guided streamers, potentially inducing new therapeutic modalities. The effects of self-organized plasma patterns could be tremendous, as highlighted in the works of Chen et al where antitumor effects are strengthened in the case of breast cancer cells exposed to stratified plasma patterns [38].
Round 2
Reviewer 3 Report
The authors did not respond to my requests (apart from the last point) relating essentially to the presentation of their results. I therefore do not change my general opinion on this manuscript, but the results presented nevertheless deserve to be published. I therefore have no objection to their publication and leave it to the discretion of the editor.
