The Electrodynamic Mechanism of Collisionless Multicomponent Plasma Expansion in Vacuum Discharges: From Estimates to Kinetic Theory

Round 1

Reviewer 1 Report

Dear Authors,

I have read and appreciated your manuscript, which I found interesting and, in my opinion, sound.

I have just two remarks before recommending publication, and two questions:

1) the English text should be revised. There are several apparent misprints, misplaced terms and/or missing words that considerably affect the reading of the text. I just list here a few examples, but I invite you to revise the English globally, since in my opinion issues of this kind can be found almost in each paragraph:

• line 16 : "...cover two the cases..."
• line 36 : "...in was shown.."
• line 70:  "...discuss at.."
• lines 72-73: "..pretending to a complete..."
• lines 108-109: " Since... , so..." 

2)  At lines 59-61 you comment about a mechanism of ion acceleration by mentioning the role of Lorentz force. What do you mean with Lorentz-force, here? I guess you refer to the electrostatic contribution, since the q(v x B ) term does not do any work? I  note in this regard that, sometimes,   with the expression Lorentz force one refers more to the q(v x B ) term than to the qE term (I am among those, for example). Maybe you could expand this sentence a little, so to clarify the sentence also for readers that use "Lorentz force" with a slightly different meaning?

3) In your quantitative analysis you make the choice of a specific ion component, that is, ions of Zn. I have two questions, related to this:

• Could you please write some words in the text about the relevance of this specific choice? (e.g., why Zn is chosen, beside of making a comparison with Ref.[4], if it is of particular experimental interest, etc.)
• I understand from your results that, since you evidence the electrostatic potential to be responsible of the ion acceleration, a (roughly inverse, I would say) dependence of the ion peak velocity on their mass should appear if  ions of different mass had been considered. I guess that  this should become  manifest also if, in place of a different metal than Zn, a mixture of two ion species with different masses (and maybe similar ion charges) had been considered. If my guess is correct, is there any reason for which you preferred not to mention these points?  (In my opinion a mention about these points could be of some interest to the reader, or otherwise, please correct my point in your reply).

4) In the system of Eqs.1 you neglect the q(v x B ). Maybe you could recall in the text since the beginning why? You say the expansion takes place in absence of background magnetic field but, does  the restriction to the non-relativistic limit -that you indeed mention later, at lines 101-102-  also play a role (e.g. in allowing to neglect  self-consistent magnetic fluctuations related to the possible appearence of  current densities) ? 

Author Response

Please, see the attached PDF file with our answers and remarks to Your comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

Line 114/115: should read: “is connected in series with R to the voltage source. Potential and voltage (=potential difference) are not the same quantity.

Line 142: 3000 “per” 2001 ?

Lines 160 and 178: use symbol, not “u” in micro-s

Line 161/162: what does it mean:  “a very little expand” and “can be widely” English needs careful checking throughout paper?

Line 171: what are “D” and “S” ?

Lines 93, 176, and elsewhere: use superscript for positive charge (+), e.g., in Zn+, Zn++, Sb+, ..

Figures 1, 2, 5 and 6: where are anode and cathode? What is plotted here? A density plot? Density is particles per cubic-m. What are sec/(kg m4)? In essence, there are 2 (maybe 3) colors. That is all? Color code must be given.

How does the discharge start? What are the initial electron and ion numbers/densities? Are particle-surface reactions and volume reactions considered? What sense does it make not to take these into account?

Conclusions are missing (partly included in discussion).

Author Response

Please, find the attached PDF file with our answers and remarks to Your comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have considered all points of this reviewer. The paper is now ready for publication.