Plume Characterization of Electrodeless Plasma Thruster with Configurable Exhaust

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper focuses on electrodeless designs, enhancing thruster durability and lifespan, aligning with the current demands for spacecraft . The content is interesting.    1. The article does not explore the impact of magnetic field distribution (e.g., gradient, shape) on plasma acceleration, even though the magnetic field is a key factor in electromagnetic acceleration. Introducing multiple magnetic field configurations (e.g., varying coil currents or magnet pole arrangements) can further verify the universality of electromagnetic mechanisms.   2. The calibration details of the self - developed retarding potential analyzer (e.g., the determination method of grid transparency coefficient K) and error sources (e.g., electronic interference, plasma sheath effects) are not sufficiently discussed. The discovery of dual energy peaks (23.5–27.3 eV and 31.3–38.8 eV) is only interpreted as "dual acceleration regions" through Gaussian fitting, without a clear explanation of their physical mechanisms.   3. Recent advances in the EPTs field (e.g., magnetic nozzle optimization, multiphysics - coupled simulation) are not adequately discussed.   4. Figure 7 (IEDF distribution) lacks specific axis units or error ranges, and Figures 11 - 12 (Gaussian fitting) lack goodness - of - fit parameters (e.g., R²). It is recommended to supplement the explanation and standardize the chart format.   5. The paper does not compare the experimental IEDF with existing theoretical models (e.g., Maxwellian distribution, two - temperature distribution), leaving the explanation of phenomena without a reference. The addition of theoretical curve overlays is suggested to visually show differences.

Author Response

Dear Reviewer 1,

Thank you for your kind processing of our manuscript!

Please find the point-by-point answers to your comment and suggestions in the .pdf file.

Thank you!

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors of the paper titled "Plume Characterization of an Electrodeless Plasma Thruster with a Configurable Exhaust" presented an analysis of an electrodeless plasma thruster. The studied thruster consists of a cylindrical gas discharge chamber, an inductor, a system of electromagnets, and a diaphragm with a variable aperture diameter. The ion energy distribution functions were obtained for varying values of the power consumption and the exit aperture diameter of the thruster.

However, the paper, in its current form, cannot be published in Symmetry Journal as it requires significant improvements.

Major Revisions:

1. Abstract: The abstract is poorly written and requires a complete rewrite.

2. Introduction: The introduction is too short, containing only nine references. This section should be expanded by incorporating more recent research on plasma thrusters, as many relevant papers have been published recently.

3. Discussion: The paper presents many interesting results, but the lack of discussion makes them difficult for readers to interpret. This section requires a thorough discussion aligned with the existing literature, citing various papers to support the conclusions.

Minor Revisions:

1. Section 2.1, Line 54: The term Electrodeless Plasma Thruster should be introduced before its acronym, formatted as Electrodeless Plasma Thruster (EPT).

2. Technical Details: More details regarding the thruster’s operational conditions, such as pressures, temperatures, thermocouples, and pressure sensors, should be included in Section 2.1 (Electrodeless Plasma Thruster).

Author Response

Dear Reviewer 2,

Thank you for your kind processing of our manuscript!

Please find the point-by-point answers to your comment and suggestions in the .pdf file.

Thank you!

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Lines 19–21:
These sentences appear to be repeated.

Line 51:
It would be helpful to include a paragraph summarizing the overall structure of your manuscript. This will guide the reader through the flow of your content.

Lines 54–55:
There seems to be repetitive wording.

Lines 67–69:
Could you clarify the maximum and minimum diameters achievable with the variable diaphragm?

Lines 69–71:
Include the data related to this measurement to support your explanation.

Figure 3:
The purpose of this photo is unclear. Consider annotating the image to highlight the key points, or replacing it with a clearer illustration.

Lines 90–92:
These lines describe changes to the hardware setup. Elaborate on which physical parameters are affected by these modifications.

Lines 104–105:
It would strengthen your methodology to explain why this particular value of -15 V was selected—was it based on prior studies or experimental evidence?

Lines 137–138:
What is meant by "triangular law"?

Figure 8:
Avoid using arrows to indicate corresponding curves—they can be hard to follow. Using legends would make the figure clearer.

You presented results for three different diameters. Do the other two setups exhibit a similar trend? Including these in the plot would provide a more comprehensive comparison.

The x-coordinate marking for the peak is unclear. A clearer method of indicating this point would help the reader understand your intention.

Lines 202–217:
Only three diameters were tested, and their values are relatively close. To more convincingly argue that gas dynamics have little influence on ion acceleration, it may be beneficial to test a wider range—perhaps including values such as 1 mm or 30 mm.

You mention randomness in Figures 9 and 10, which is valid. However, Figure 8 also displays similar irregularities, especially on the right half of the curves. This raises questions about drawing a strong conclusion from Figure 8 while interpreting Figures 9 and 10 differently.

Furthermore, even if gas dynamics are ruled out as a major factor, there is not yet sufficient evidence in the manuscript to support the claim that electromagnetic acceleration mechanisms are dominant.

Lines 219–222:
The phrasing here is unclear. A revision for clarity and fluency would be appreciated.

Figure 11:
What causes the third peak? Provide an explanation.

Lines 236–239:
This observation may not be consistent across all your results. In Figures 8, 9, and 10, several datasets show a bump on the left side with a smoother right half. Please clarify.

Lines 240–242:
What’s this conclusion based on? There’s no figure clearly showing this.

 

Author Response

Dear Reviewer 3,

Thank you for your kind processing of our manuscript!

Please find the point-by-point answers to your comment and suggestions in the .pdf file.

Thank you!

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Issues are addressed. 

Author Response

Dear Reviewer 1,

Thank you for your kind support!

Reviewer 2 Report

Comments and Suggestions for Authors

I am satisfied with the corrections addressed by the authors. The paper can be published in Symmetry in its corrected version.

Author Response

Dear Reviewer 2,

Thank you for your kind support!

Reviewer 3 Report

Comments and Suggestions for Authors

You answered most of the previous comments. However, as per Comment 11: Even if gas dynamics are ruled out as a major factor, there is not yet sufficient evidence in the manuscript to support the claim that electromagnetic acceleration mechanisms are dominant. Please provide supporting experiment results or explicitly explain why you can confirm the importance of electromagnetic acceleration by ruling out gas dynamics.

Author Response

Dear Reviewer 3,

Thank you for your kind support!

Please find attached the answer to your question.

Author Response File: Author Response.pdf