The Double-Nozzle Technique Equipped with RF-Only Funnel and RF-Buncher for the Ion Beam Extraction into Vacuum

Round 1

Reviewer 1 Report

 

The aim of this work is the design of an efficient setup for the photoionization spectroscopy studies of heavy radioactive atoms, such as, for example, Nobelium.

 

Therefore, the paper describes a theoretical study, representing a continuation of a previous article on this review, where the author presented the double-nozzle technique, in view of its application in gas-jet resonance ionization laser spectroscopy.

 

The development of the ideas in the “old” text consists in a new proposal, where the double-nozzle is directly coupled to an RF-only funnel and a cylindrical RF-buncher, other components designed by the author and already tested in several facilities.

 

This new setup, to be eventually installed at GSI, is much more straightforward than a conventional RFQ device and should obtain a higher efficiency, if compared with the reference experimental system for the author.

 

The paper discusses an ample and impressive collection of Monte Carlo simulations, based on gas dynamics: main results are related to 8 different combinations of gas stagnation pressures in the gas cell and in the double-nozzle, the graphic description of the supersonic and subsonic gas flow structure, the values of total ion beam extraction efficiency into a vacuum for all the 8 calculation variants, the comparison with the conventional technology of in-gas-jet laser resonance spectroscopy.

 

The simulations are encouraging, as, for example, they report on an increase in the efficiency for a factor >2, when both the back systems are formed by the new RF-only funnel and buncher, while the double-nozzle is used instead of the conventional one.

 

The paper is sound and the scientific content, in my opinion, deserves publication in Atoms, but only after a thorough revision of the English language, as there are many mistypes and repetitions in the text, which does not adequately flow.

 

 

As I already told you in my general comment, the quality of the English language is pretty poor. I strongly recommend a very careful revision, eliminating repetitions and mistypes, and trying to make the paper more fluent as a whole. Sorry, the list of mistakes is too long to be presented here.

Author Response

Many thanks to Reviewer 2

Author Response File: Author Response.pdf

Reviewer 2 Report

This submitted paper describes the results of gas dynamic simulations of an underexpanded supersonic free jet formed by a proposed novel double nozzle system that is coupled to a RF-funnel. These simulations are made concurrently with atom trajectory simulations including simulation of performance of two-step laser ionization on a heavy atoms in the jet. The simulations are performed in a several different variants (different pressure conditions) and the resulting vacuum, jet and ion optical results are presented and compared. For example a comparison to RF-only funnel and RF-buncher is done with a "conventional" nozzle and the resulting differences in the gas flow structure, ion transportation efficiency and pumping requirements are presented.

These results are then used to explore the conditions and geometry in which the RF-only funnel with the double-nozzle results to the best ion transportation for superheavy nobelium isotopes.

The article proposes modification in connection with JetRIS project at GSI, Darmstadt. This is part of broader field of nuclear physics research specifically related to high resolution optical spectroscopy using laser resonance ionization on exotic nuclear isotopes. Performing of laser spectroscopy in an expanding supersonic noble gas jet is currently highly topical issue in the field due to very favorable conditions and high efficiency. Therefore a publication related this is definitely of of high interested. There are, however, short-comings which need, minimally at least partly, to be addressed before this can be accepted for publication as a stand-alone paper.

1. One of the major short-coming of this publication is the very narrow scope with results sole based on simulations and these results are already being built on part of another set of simulations only results (ref 1.). Therefore the manuscript in parts reads like a scientific report on simulations with the simulation results given as a parameter-dump tables and figures. Although some of the results are potentially quite useful, these results would be much more valuable if added to a broader investigation such as to experimental results or even more broader discussion. For example what the origin of the differences in the simulated efficiencies. What specific simulation results mean for example for the in-jet laser resonance ionization not only as overlap and efficiency, but also resonance width, Doppler broadening, shift etc (if there is significance). It is not clear in the manuscript why results in Figure 10 and 11 are presented. Why longitudinal velocity and radial velocity are important?

It would be highly recommended that this publication is extended with some form of experimental data. This could be a simple pressure test of the double-nozzle with a dummy rf-nozzle. Additionally it could include measurements i.g with a small pitot probe to probe Mach disk position.

2. The manuscript should be considered to be shortened. Is it really necessary to present all possible variations and results. The number of figures should be considered for example. Why are the figures 10 and 11 presented? Figure 8 demonstrates the detailed structure of the supersonic jet in the region of the RF, what is it that we see in Figure 8 that we cannot see in the figure 7?

Tables 11 and 12 present simulations results of the GSI nozzle with a stagnation pressures of 200 and 300 mbars. These results are not different enough to warrant separate tables. The differences can be described shortly in written text.

Author should carefully think what is important for a concise presentation.

3. The simulations methodologies of the paper are not described adequately. The paper describes simulations only as "detailed gas dynamic simulations" and "Monte Carlo" simulations without mentioning which package or code has been used. Ref. 1 one mentions VARJET code. Is this the code that has been used for the simulation? What about the Monte Carlo simulations? Is it a own home-brew code or a simulation package such as Simion? As this paper is solely based on simulation results these need to be described in detail.

4. Some of the references are self-citations to conference presentations without peer reviewing. For example reference 5, 11-13 include non-peer-reviewed scientific reports and presentations by the author from as early as 2001. If available, I would recommend adding citing peer-reviewed scientific publications containing some of these results instead or setups having used these results in their development.

Some more detailed comments.

Page 1. Section 1. Paragraph 2. line 1:
- Change "d in [1} s" to "d in [1] s"

Page 2.
Figure 1:
- Please add scale bar or a ruler to better understand the actual dimensions similarly to figure 3.

Paragraph 1:
- It would be good to mention here why nobelium-254. JetRIS project, what is the goal.

Paragraph 3
- Even though the reader can go to the reference [1] to find out detailed information about the nozzle, this paper should contain still basic information about the "GSI nozzle" and the "double-nozzle", such as the throat diameter, design Mach number if applicable, etc.

- This should also note the ambient pressure of the expansion chamber if available.

Page 2 Paragraphs 4. Page 3. Figure 2: The sentence "Simulation results for cumulative fractions of nobelium-254 atomic beam inside the diameter of 8 mm for different downstream distances from the GSI nozzle exit." This is not clear enough what is the presented result here. Is this meant to be the cumulative fraction of No-254 atoms as a function of the laser beam radius at different distances from the nozzle exit. Please rewrite.

Page 3. The paper states a suggestion of replacing the conventional bent RFQ in the gas-jet chamber by a simple RF-only funnel placed on the axis of the gas-jet chamber. This suggestion I don't understand. Isn't the idea of the S-shaped radio frequency quadrupole that it allows the laser access to the jet along the axis close to source? If this is replaced with on-axis funnel, it can complicate the laser access by need of additional kickers or other elements further downstream.

Page 4.

Second to last paragraph. This paper assumes ionization efficiency of 100% when exposed to both lasers? This should be mentioned.

Page 5.
Table 2. Row: "Background pressure in gas-je tchamber Pbg (mbar)" Please use decimal point instead of comma.

Figure 4. Please include higher resolution image. Now it is difficult to figure out the exponent numbers in the density scale.

Pages 5-6.

The table 2 lists results of gas dynamic simulations in different upstream pressure conditions. Different pressures would cause the location of the Mach disk as well as the diameter to change and therefore I would assume the coupling to the RF-funnel. Was this studied? Or is it the RF-funnel interaction with the jet that determines the Mach disk position?

Page 7.

Section 4.
The variants refer to the table 3 variants. Please state this explicitly.

Page 8.

Table 3.
The atomic beam radius unit listed in the table needs to be mentioned [mm].

Paragraph 2. The simulation results for longitudinal and radial velocity spreads are given. The article should consider mentioning the importance of these numbers. Are these important parameters, i.g. for the broadening mechnisms of the resonances in the laser ionization process.

Page 10.

Paragraph 1. In other words each atom sees at least one simultaneous pulse for Laser-1 and Laser-2.

Page 11. Change "Rf-funnel-RFbuncher DC bias" to "RF-funnel-RF-buncher DC bias"

Page 13. Second paragraph. Here the author should explore the reasons more in detail to the lower efficiency compared to the efficiencies in table 7.

Page 14-15 Last paragraph. Please revise the text less colloquial.

English is partly too colloquial. Please revise.

Author Response

Many thanks to Reviewer 2

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Please see the attached comments to authors responses.

Comments for author File: Comments.pdf

Author Response

Many thanks to the Reviewer 2 for cooperation

Author Response File: Author Response.pdf