Review Reports - Research on Sheet Electron Beam Quadrupole Permanent Magnet Focusing System for Terahertz Vacuum Devices

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper proposes a quadrupole permanent magnet (QPM) focusing system for terahertz sheet beam traveling wave tubes (TWTs), which enables the efficient transmission of sheet electron beams. However, the logical coherence of the entire paper is poor, and the key processes, including theoretical analysis, system design, experimental testing, and feedback simulation are not elaborated in detail. Overall, the paper is relatively rough with insufficient content and limited innovativeness. Specific revision suggestions are as follows:

1. The quadrupole permanent magnet focusing system has been discussed in numerous existing studies. The authors are requested to supplement the international research progress of related technologies in the introduction section, and clearly compare this work with previous studies to specify the innovativeness of the proposed system.

2. Multiple formulas are listed in Chapter 2, yet they have no explicit correlation with the subsequent design process of the QPM system. First, the reason for designing the magnetic field as 1.5 times the Brillouin magnetic field (0.94T/0.64T) needs to be elaborated. For magnetic field design, the authors should supplement the analysis of the influence of different scaling coefficients on electron beam transmission. In addition, although the design formulas for the transverse magnetic field are given, the consideration and design method of the transverse magnetic field distribution of the QPM focusing system adopted in this paper remain unclear and need to be explained in detail.

3. The schematic diagram in Figure 1 is overly rough and fails to clearly illustrate the composition and connection structure of the sheet beam TWT for readers. In combination with the magnetic field distribution in Figure 4, magnetic shielding was not considered in the magnetic field design, which is an essential design step for most electron guns and should be supplemented and optimized.

4. Corresponding to the above issue, Figure 6 presents the electron beam compression envelope. According to the research idea of the paper, electrons are subjected to a strong magnetic field (>6000 Gs) immediately after emission. The compression process of the electron beam under such a strong magnetic field involves a complex force-bearing process, which is quite different from the reported design methods of sheet beam electron guns. The authors are required to elaborate on the design method of the electron gun under this specific magnetic field condition in detail.

5. For the design of the magnetic focusing system, the authors should supplement the 3D magnetic field distribution map to fully reflect the magnetic field characteristics of the QPM system. The paper mentions the adoption of two types of magnets with different residual magnetism to improve magnetic field uniformity, but the specific design strategy and the underlying mechanism of how this design improves magnetic field uniformity are not explained and need to be supplemented in detail.

6. Figure 5 is not a PIC simulation result but the calculation result of the tracking module; the authors are requested to verify and correct the relevant annotation. In addition, to effectively verify the focusing effect of the magnetic field, the authors should supplement the schematic diagrams of the electron gun and the RF channel involved in the experiment/simulation.

7. The deviation between the measured and designed magnetic field distributions in Figure 4 (approximately 5%) should be quantitatively and qualitatively analyzed. On this basis, the authors need to clarify how such a variation in magnetic field intensity affects the electron beam envelope shown in Figure 6.

8. There are several imprecise academic descriptions in the paper:

(a) The statement "The former is smaller in volume and weight, but has a limited magnetic field of 0.6T, while the latter can generate a larger magnetic field of around 1.5T and both of them do not require power supply to drive." lacks citations for the source of the data, and the conclusion drawn is overly arbitrary without sufficient supporting evidence.

(b) The term "test mold" in Figure 3 is presumably a typo and needs to be corrected and verified.

(c) The annotation of 9500 Gs in Figure 4 is ambiguous, as the measured maximum magnetic field intensity is only 9479 Gs; the specific meaning of this annotation should be clearly explained.

(d) In Figure 6, the physical meanings of the ± directions are not specified; the authors should add corresponding annotations to clarify them.

Author Response

Response to the first reviewer:

Q1:

The quadrupole permanent magnet focusing system has been discussed in numerous existing studies. The authors are requested to supplement the international research progress of related technologies in the introduction section, and clearly compare this work with previous studies to specify the innovativeness of the proposed system.

Response:

Thank you very much for the comments. The reviewer is right, it is true that the QPM has been investigated before, however, for the latest very fast development of high frequency THz vacuum device, the new requirement for the QPM exists to confine the tiny electron beam with high current density up to 400 A/cm² to obtain high beam transmission ratio and then high power output from the TWTs. In this paper, our new design lies in the uniform focusing magnetic field of a terahertz band sheet beam TWT, it is different from the previous scheme. We have revised the paper accordingly based on the above response, the international research progress of QPM is added in the thesis.

The following text has been added to the paper for your reference:

“Research of quadrupole permanent-magnet has been carried out these years. A permanent magnet quadrupole doublet lens with strong-focusing is designed and manufactured to solve the problem of irregular beam spots produced by the weak focusing of conventional solenoid-focusing systems in low-energy electron irradiation accelerators[12]. By introducing a pair of centimeter-sized PMQs in front of the EMQs for beam prefocusing, the beam's transverse size is quickly compressed, enabling transmission of highly divergent protons in the compact laser plasma accelerator[13]. Using a superposition of solenoid and sextupole fields, the electron confinement in the quadrupole field is weaker than in conventional ECR ion sources in plasma breakdown and decay transient measurements of the bremsstrahlung power flux[14]. A permanent magnet based on the quadrupole magnet is designed to replace different sizes of quadrupole magnets in accelerators, greatly improving systematization[15]. A Halbach-2 type quadrupole magnet was designed as a final focus lens for colliders and similar projects[16]. As compared to traditional magnets, permanent magnets can effectively reduce energy consumption and eliminate the impact of current ripple and the water cooling system on beam current[17], which are the main advantages of the usage of quadrupole permanent-magnet in accelerators, colliders and electron cyclotron resonance ion sources.”

The new requirement for the QPM exists to confine the tiny electron beam with high current density up to 400 A/cm2 to obtain high beam transmission ratio and then high power output from the TWTs. In this paper, our new design lies in the uniform focusing magnetic field of a terahertz band sheet beam TWT, which is different from the previous scheme.

Q2:

Multiple formulas are listed in Chapter 2, yet they have no explicit correlation with the subsequent design process of the QPM system. First, the reason for designing the magnetic field as 1.5 times the Brillouin magnetic field (0.94T/0.64T) needs to be elaborated. For magnetic field design, the authors should supplement the analysis of the influence of different scaling coefficients on electron beam transmission. In addition, although the design formulas for the transverse magnetic field are given, the consideration and design method of the transverse magnetic field distribution of the QPM focusing system adopted in this paper remain unclear and need to be explained in detail.

Response:

Thank you very much for the comments. Formula (1) and (2) are used in the design process, while formula (3) to (8) are listed to show the design boundaries and check the results of the magnetic focusing system.

According to the design experience of the magnetic focusing system of circular electron beam, when the magnetic field of the system reaches more than 1.5 times of Brillouin magnetic field, the fluctuation amplitude of the edge of electron beam will be significantly reduced, which is beneficial to the stable transmission of electron beam. However, limited by the magnet manufacturing and assembling technology, it is hard to generate a 2-times of Brillouin magnetic field. Thus, we choose the focusing effect of 1.5 times of Brillouin magnetic field, and simulation result shows that the magnetic system can meet the focusing requirements.

For the transverse magnetic field, the device is placed in the center of x direction and y direction of the magnetic system. However, due to the manufacturing and assembling process of the magnets, the transverse magnetic field generated by the QPM system cannot be completely eliminated. Test results show that the maximum magnetic field along x direction is 180 Gauss, while that along y direction is 290 Gauss. Therefore, the annular soft iron material is used in the gun area of the device to shield the transverse magnetic field at the edge of the electron beam, and it can be predicted by the simulation result that only tens of Gauss remains in the transverse magnetic field in the gun area after shielding. The test result of Bx and By is shown as the following figure, which is the magnetic field before shielding.

We have revised the paper accordingly based on the magnetic field design process.

The following text has been added to the paper for your reference:

“According to the design experience of the magnetic focusing system of circular electron beam, when the magnetic field of the system reaches more than 1.5 times of Brillouin magnetic field, the fluctuation amplitude of the edge of electron beam will be significantly reduced, which is beneficial to the stable transmission of electron beam. Due to the magnet manufacturing and assembling technology, it is difficult to achieve 1.2 to 1.3 Tesla magnetic field (2 times of Brillouin magnetic field) based on NdFeB materials of conventional brands under the current magnetic system structure. Moreover, we have tried to calculate the focusing effect of electron beam under 2 times of Brillouin magnetic field, which is improved to some extent compared with that of 1.5 times. However, at present, the focusing effect of 1.5 times of Brillouin magnetic field magnetic system can meet the design requirements.”

“In terms of transverse magnetic field, the device is placed in the center of x direction and y direction of the magnetic system. However, due to the manufacturing and assem-bling process of the magnets, the transverse magnetic field generated by the QPM system cannot be completely eliminated. Test results show that the maximum magnetic field along x direction is 180 Gauss, while that along y direction is 290 Gauss. Therefore, the annular soft iron material is used in the gun area of the device to shield the transverse magnetic field at the edge of the electron beam, and it can be predicted by the simulation result that only tens of Gauss remains in the transverse magnetic field in the gun area after shielding. ”

Q3:

The schematic diagram in Figure 1 is overly rough and fails to clearly illustrate the composition and connection structure of the sheet beam TWT for readers. In combination with the magnetic field distribution in Figure 4, magnetic shielding was not considered in the magnetic field design, which is an essential design step for most electron guns and should be supplemented and optimized.

Response:

Thank you very much for the comments. We replace Figure 1 with a new one, which includes the composition (cathode, focusing electrode, anode and slow wave structure) and connection structure (input and output waveguide) of the sheet beam TWT. The magnetic shielding was considered in the magnetic field design, the shell material of the electron gun is made of Fe-Co-Ni Kovar alloy(4J33), which has remarkable magnetism and can shield part of the magnetic field from entering the gun area. At the junction of the gun and the slow wave structure, a ring-shaped soft iron material component was adopted, which can shield the transverse magnetic field generated by the QPM system, as shown in the Figure 1.

Figure 1. The structural diagram of the magnetic system, purple and blue for magnets, gray for iron and aluminum. The shielded electron gun structure, which includes cathode, guide, anode, slow wave structure and connection structure(input and output waveguide) of the sheet beam TWT.

The following text has been added to the paper for your reference:

“We adopt a magnetic field shielded electron gun structure, as shown in the figure 1. The shell material of the electron gun is made of Fe-Co-Ni Kovar alloy(4J33), which has remarkable magnetism and can shield part of the magnetic field from entering the gun area. At the junction of the gun and the slow wave structure, a ring-shaped soft iron material component was adopted, which can shield the transverse magnetic field generated by the QPM system.”

Q4:

Corresponding to the above issue, Figure 6 presents the electron beam compression envelope. According to the research idea of the paper, electrons are subjected to a strong magnetic field (>6000 Gs) immediately after emission. The compression process of the electron beam under such a strong magnetic field involves a complex force-bearing process, which is quite different from the reported design methods of sheet beam electron guns. The authors are required to elaborate on the design method of the electron gun under this specific magnetic field condition in detail.

Response:

Thank you very much for the comments. The magnetic shielding was considered in the magnetic field design, and electrostatic compression happens when the electrons were emitted from the cathode, which leads to the stable transmission of the beam. The compression of the long edge is about 3.5, while the compression of the short edge is about 7.

We adopt a magnetic field shielded electron gun structure, as shown in the Figure 1. For the direction of electron beam transmission, the magnetic field in the electron gun area and the magnetic field outside the gun have great changes under the action of the magnetic shield of the gun. When traveling through the anode, the electrons will be immediately converged by a strong magnetic field, as shown in Figure 4. The strong magnetic compression will make the electrons instantly converge, leading to the primary compression of the electron beam ,and the beam is limited in the beam tunnel.

The reference documents of shielded electron gun designing are as followed.

[21]Wang J, Wan Y, Li X, et al. Continuous wave operation of a ka-band broadband high-power sheet beam traveling-wave tube[J]. IEEE Electron Device Letters, 2021, 42(7): 1069–1072.

[22]Li X, Wang J, Wan Y, et al. A wideband high-voltage longitudinal output structure for ka-band sheet beam traveling-wave tubes[J]. IEEE Transactions on Microwave Theory and Techniques, 2021, 69(4): 2042–2047.

[23]Yin P. Research on the sheet electron beam optical system of traveling wave tube[D]. Chengdu: University of Electronic Science and Technology of China, 2022.

Figure 4. Comparison of designed (black line) and measured (red dot) magnetic field. The blue line shows the magnetic field in the shielded electron beam tunnel.

The following text has been added to the paper for your reference:

“For the direction of electron beam transmission, the magnetic field in the electron gun area and the magnetic field outside the gun have great changes under the action of the magnetic shield of the gun. When traveling through the anode, the electrons will be immediately converged by a strong magnetic field, as shown in Figure 4. The strong magnetic compression will make the electrons instantly converge, leading to the primary compression of the electron beam ,and the beam is limited in the beam tunnel. Similar design methods can be found in the following documents[21-23].”

Wang J, Wan Y, Li X, et al. Continuous wave operation of a ka-band broadband high-power sheet beam traveling-wave tube[J]. IEEE Electron Device Letters, 2021, 42(7): 1069–1072.
Li X, Wang J, Wan Y, et al. A wideband high-voltage longitudinal output structure for ka-band sheet beam traveling-wave tubes[J]. IEEE Transactions on Microwave Theory and Techniques, 2021, 69(4): 2042–2047.
Yin P. Research on the sheet electron beam optical system of traveling wave tube[D]. Chengdu: University of Electronic Science and Technology of China, 2022.

Q5:

For the design of the magnetic focusing system, the authors should supplement the 3D magnetic field distribution map to fully reflect the magnetic field characteristics of the QPM system. The paper mentions the adoption of two types of magnets with different residual magnetism to improve magnetic field uniformity, but the specific design strategy and the underlying mechanism of how this design improves magnetic field uniformity are not explained and need to be supplemented in detail.

Response:

Thank you very much for the comments. The three-dimensional magnetic field distribution is shown in the following figure. The test results show that the maximum magnetic field along x direction is 180 Gauss, while that along y direction is 290 Gauss. After shielding, the magnetic field along z direction reduces from 0.9 Tesla to hundred level. It can be predicted by the simulation result that only tens of Gauss remains in the transverse magnetic field in the gun area after shielding.

For the specific design strategy and the underlying mechanism, space must be reserved for the input and output systems of TWT, which leads to a disconnection area in the system. Thus, a “valley” will exist in the middle of the magnetic field, as shown in figure 4(z=0). Instead of one magnetic field loop in the traditional system, the two kinds of residual magnetivities materials are used to improve the uniformity of magnetic field. When two kinds of NdFeB materials with different residual magnetivities are used, an additional auxiliary magnetic field loop is constructed inside the main magnetic field loop, which can make up for the disconnection effect in the space area and improve the “valley”, making the magnetic field uniform area longer.

In the following figure, the simulation result of magnetic field of all magnets replaced by Br=1.42T is shown, as a comparison. We can see that the ripple of the magnetic field can be decreased by using a couple of different residual magnetivities materials magnets.

The following text has been added to the paper for your reference:

For the specific design strategy and the underlying mechanism, space must be reserved for the input and output systems of TWT, which leads to a disconnection area in the system. Thus, a “valley” will exist in the middle of the magnetic field, as shown in figure 4(z=0). Instead of one magnetic field loop in the traditional system, the two kinds of residual magnetivities materials are used to improve the uniformity of magnetic field. When two kinds of NdFeB materials with different residual magnetivities are used, an additional auxiliary magnetic field loop is constructed inside the main magnetic field loop, which can make up for the disconnection effect in the space area and improve the “valley”, making the magnetic field uniform area longer.

Q6:

Figure 5 is not a PIC simulation result but the calculation result of the tracking module; the authors are requested to verify and correct the relevant annotation. In addition, to effectively verify the focusing effect of the magnetic field, the authors should supplement the schematic diagrams of the electron gun and the RF channel involved in the experiment/simulation.

Response:

Thank you very much for the comments, the mistake has been corrected. The schematic diagrams of the electron gun and the RF channel involved in the simulation has been placed and marked in Figure 1.

Q7:

The deviation between the measured and designed magnetic field distributions in Figure 4 (approximately 5%) should be quantitatively and qualitatively analyzed. On this basis, the authors need to clarify how such a variation in magnetic field intensity affects the electron beam envelope shown in Figure 6.

Response:

Thank you very much for the comments. The error is caused by the manufacturing and assembling of the magnetic system. The whole magnetic system is formed by splicing, so that the magnetic declination angle of each magnet cannot be completely horizontal or vertical, so a deviation of about 5% is produced, which meets our expectations. Because of the “valley” in the magnetic field, the electron beam will expand slightly at the “valley” point, and the expansion in x direction is about 1.8%, while that in y direction is about 8.7%. The final result shows that the expanded beam can travel through the beam channel, with some under-control fluctuations.

The following text has been added to the paper for your reference:

The error is caused by the manufacturing and assembling of the magnetic system. The whole magnetic system is formed by splicing, so that the magnetic declination angle of each magnet cannot be completely horizontal or vertical, so a deviation of about 5% is produced, which meets our expectations. Because of the “valley” in the magnetic field, the electron beam will expand slightly at the “valley” point, and the expansion in x direction is about 1.8%, while that in y direction is about 8.7%. The final result shows that the expanded beam can travel through the beam channel, with some under-control fluctuations.

Q8:

There are several imprecise academic descriptions in the paper:

Q8(a):

The statement "The former is smaller in volume and weight, but has a limited magnetic field of 0.6T, while the latter can generate a larger magnetic field of around 1.5T and both of them do not require power supply to drive." lacks citations for the source of the data, and the conclusion drawn is overly arbitrary without sufficient supporting evidence.

Response:

Thank you very much for the comments. The comparison is between PPM focusing system and PM focusing system, we find a reference document and revise the paper accordingly based on the above response. When focusing magnetic field with good uniformity and high current density beam compatibility is required, the PM focusing system will be chosen, as we do in the thesis.

At present, the peak value of the periodical permanent magnetic field made of SmCo materials can only reach about 8000 Gauss, while the average magnetic field is about Gauss[11], which is difficult to meet the demand of focusing the THz band sheet beam TWT. As a comparison, the QPM system we proposed can generate a magnetic field about 1Tesla, which is suitable for the focusing of the sheet electron beam.

The reference document is:

[11]Mihara T , Iwashita Y , Kumada M ,et al. Variable Permanent Magnet Quadrupole[J].IEEE Transactions on Applied Superconductivity, 2006, 16(2):224-227.

The following text has been added to the paper for your reference:

“At present, the peak value of the periodical permanent magnetic field made of SmCo materials can only reach about 8000 Gauss, while the average magnetic field is about Gauss[11], which is difficult to meet the demand of focusing the THz band sheet beam TWT. As a comparison, the QPM system we proposed can generate a magnetic field about 1Tesla, which is suitable for the focusing of the sheet electron beam.”

Mihara T , Iwashita Y , Kumada M ,et al. Variable Permanent Magnet Quadrupole[J].IEEE Transactions on Applied Superconductivity, 2006, 16(2):224-227.

Q8(b):

The term "test mold" in Figure 3 is presumably a typo and needs to be corrected and verified.

Response:

Thank you very much for the comments, the word “mold” is replaced by “mould”.

Figure 3. The test setup of the QPM system.

Q8(c)

The annotation of 9500 Gs in Figure 4 is ambiguous, as the measured maximum magnetic field intensity is only 9479 Gs; the specific meaning of this annotation should be clearly explained.

Response:

Thank you very much for the comments, the maximum of magnetic field is 9479Gs, Figure 4 has been corrected, the result of the magnetic field in the electron beam tunnel is added in figure 4.

Figure 4. Comparison of designed (black line) and measured (red dot) magnetic field. The blue line shows the magnetic field in the shielded electron beam tunnel.

Q8(d):

In Figure 6, the physical meanings of the ± directions are not specified; the authors should add corresponding annotations to clarify them.

Response:

Thank you very much for the comments, z₀ is the device exact position set along z direction, z₀+0.2mm and z₀-0.2mm is the device set ±0.2mm shift away from the exact position along z direction. The corresponding annotations are added in the thesis.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript reports a quadrupole permanent magnet (QPM) focusing system for THz sheet-beam vacuum devices.

Here are my comments:

-Expand the introduction to better summarize prior sheet-beam focusing approaches and add a short, explicit novelty statement.

-The manuscript mentions higher power motivation, but it would benefit from a brief paragraph listing other levers to increase TWTS output power/efficiency beyond focusing, such as increasing beam current.

-Ensure claims that are not your own are supported by citations, and apply consistent referencing throughout the paper such as in line 47, 48.

-Explain equations immediately after they appear and define all symbols/coordinates at first use. For example, Eq. (1) uses z without defining the coordinate system until later discussion around Eq. (6).

Author Response

Response to the second reviewer:

Q1:

Expand the introduction to better summarize prior sheet-beam focusing approaches and add a short, explicit novelty statement.

Response:

Thank you very much for the comments. For sheet beam devices, the typical examples are the sheet beam klystrons [5], [6] and EIKs [7]. For low frequency TWTs, the periodical permanent magnetic focusing system are widely used. However, for sheet beam TWT, especially terahertz band sheet beam TWT, the periodical permanent magnetic field cannot meet the requirement of beam focusing. Thus, “wiggler” magnetic focusing system[8], PCM magnetic focusing system[9] and uniform magnetic focusing systems[4] are applied in the research of the device. The QPM magnetic focusing system is a kind of uniform magnetic focusing system.

We have revised the paper accordingly based on the above response.

The following text has been added to the paper for your reference:

“The typical examples are the sheet beam klystrons [5], [6] and EIKs [7]. For low frequency TWTs, the periodical permanent magnetic focusing system are widely used. However, for sheet beam TWT, especially terahertz band sheet beam TWT, the periodical permanent magnetic field cannot meet the requirement of beam focusing. Thus, “wiggler” magnetic focusing system[8], PCM magnetic focusing system[9] and uniform magnetic focusing systems[4] are applied in the research of the device. The QPM magnetic focusing system is a kind of uniform magnetic focusing system.”

“The new requirement for the QPM exists to confine the tiny electron beam with high current density up to 400 A/cm2 to obtain high beam transmission ratio and then high power output from the TWTs. In this paper, our new design lies in the uniform focusing magnetic field of a terahertz band sheet beam TWT, which is different from the previous scheme.”

Q2:

The manuscript mentions higher power motivation, but it would benefit from a brief paragraph listing other levers to increase TWTS output power/efficiency beyond focusing, such as increasing beam current.

Response:

Thank you very much for the comments.

Raising the operation voltage, beam current or beam density, interaction efficiency are the common methods to improve the output power of the device. Besides, raising coupling impedance and decreasing the transmission loss are feasible methods.

Sheet electron beam is an effective method to enhance the power of devices through significantly increasing the beam current. By increasing the size of the beam, the device can generate higher output power on condition of similar beam density, which decreases the difficulties of the voltage withstanding performance of the material adopted in the device.

We have revised the paper accordingly based on the above response.

The following text has been added to the paper for your reference:

“Raising the operation voltage, beam current or beam density, interaction efficiency are the common methods to improve the output power of the device. Besides, raising coupling impedance and decreasing the transmission loss are feasible methods. Sheet electron beam is an effective method to enhance the power of devices through significantly increasing the beam current. By increasing the size of the beam, the device can generate higher output power on condition of similar beam density, which decreases the difficulties of the voltage withstanding performance of the material adopted in the device.”

Q3:

Ensure claims that are not your own are supported by citations, and apply consistent referencing throughout the paper such as in line 47, 48.

Response:

The reference document is:

[11]Mihara T , Iwashita Y , Kumada M ,et al. Variable Permanent Magnet Quadrupole[J].IEEE Transactions on Applied Superconductivity, 2006, 16(2):224-227.

The following text has been added to the paper for your reference:

At present, the peak value of the periodical permanent magnetic field made of SmCo materials can only reach about 8000 Gauss, while the average magnetic field is about Gauss[11], which is difficult to meet the demand of focusing the THz band sheet beam TWT. As a comparison, the QPM system we proposed can generate a magnetic field about 1Tesla, which is suitable for the focusing of the sheet electron beam.

Mihara T , Iwashita Y , Kumada M ,et al. Variable Permanent Magnet Quadrupole[J].IEEE Transactions on Applied Superconductivity, 2006, 16(2):224-227.

Q4:

Explain equations immediately after they appear and define all symbols/coordinates at first use. For example, Eq. (1) uses z without defining the coordinate system until later discussion around Eq. (6).

Response:

Thank you very much for the comments, z direction is the direction of electron transmission, and the definition is added in the thesis.

The following text has been added to the paper for your reference:

“z direction is the direction of electron transmission”

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

None