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Compact bulk-machined electromagnets for quantum gas experiments
by K. Roux, B. Cilenti, V. Helson, H. Konishi, J. P. Brantut
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Submission summary
| Authors (as registered SciPost users): | Jean-Philippe Brantut · Hideki Konishi · Kevin Roux |
| Submission information | |
|---|---|
| Preprint Link: | https://arxiv.org/abs/1901.08791v2 (pdf) |
| Date submitted: | 2019-03-18 01:00 |
| Submitted by: | Brantut, Jean-Philippe |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approach: | Experimental |
Abstract
We present an electromagnet combining a large number of windings in a constrained volume with efficient cooling. It is based on bulk copper where a small pitch spiral is cut out and impregnated with epoxy, forming an ensemble which is then machined at will to maximize the use of the available volume. Water cooling is achieved in parallel by direct contact between coolant and the copper windings. A pair of such coils produces magnetic fields suitable for exploiting the broad Feshbach resonance of $^6$Li at 832.2 G. It offers a compact and cost-effective solution for quantum gases experiments.
Author comments upon resubmission
The revised version addresses all the criticism of the referees. In particular, the points raised by both referees concerning the particular geometry used in the actually implementation, as well as the derivation and motivation for the equations (1) and (2) are clarified in this new version.
List of changes
Changes requested in report 2:
1 - We have removed ‘parallel’ from the introduction since it was indeed used in an ambiguous way.
2 - This is now explicitly stated in the text.
3 - We have included more details in the figure. The caption has been expanded in order to provide a more detailed description of the figure.
4 - We have rewritten this paragraph. The detailed derivation of the various equations are now presented in the new appendix, which confirms that the result presented is correct.
5 - We have added a sentence to clarify the purpose of the figure, and the relationship with cooling efficiency.
6 - We have followed this recommendation.
7 - The new figure 3 now presents the field distribution for the pair of coils as implemented in the experiment, and numbers for the field curvature are stated in the text.
8 - The measured inductance is of the coil is now stated, as well as an estimate of the temperature sensitivity of the magnetic field.
9 - This is an interesting question. Wire erosion machines are not uncommon in university workshops. However, we did not mention explicit costs because (i) the machining cost will strongly depend on the actual capabilities of the external company, in particular the experience it has with cutting thin wires without them twisting and breaking the wire, (ii) the actual cost of manufacturing for our system is strongly influenced by the high labor cost and strong currency in Switzerland, which is probably not representative of what a well chosen external contractor could offer. Should another team wish to reproduce the technique, we are happy to provide more technical details on our experience upon request, so as to reduce the cost and time.
10 - This sentence has been reformulated.
11 - We thank the referee for pointing our this issues, which have been corrected in the new version of the paper.
Changes requested in report 1:
1- We have modified the figure following these recommendations.
2- We have included an appendix with the derivation of Eq 1
3 - Our discussion of the roles of conduction and convection as well as the Nusselt number was confusing. We have rewritten section 2 in order to clarify these discussions.
4 - The intended use of the coils is in pairs with a Helmholtz configuration, such that at the position of the atoms there is no gradient but a finite curvature. We have now included a new version of figure 3 where the simulated field distribution for this configuration is shown. We also state numbers concerning the field curvature in the text.
Concerning temporal variations due to thermal heating of the coils, we thank the referee for this insightful question. Section 4.2 now includes a paragraph describing the expected variation of magnetic field at fixed current, due to thermal expansion of the coil.
5 - Indeed titanium was primarily chosen for its non magnetic character. Titanium has similar electrochemical potential as stainless steel, and is more cathodic than copper. In our configuration,the surface of titanium exposed to water is very small. This is the recommended configuration for mitigating galvanic corrosion (see for exemple the standard MIL-STD-889C). We use deionized water for the cooling fluid, which further reduces the risk of corrosion.
6 - The temperature was not regulated, but we did not notice variations of the water temperature while acquiring the data.
7 - The relevant sentences have been corrected.
Current status:
Reports on this Submission
Report #2 by Ryan Thomas (Referee 1) on 2019-3-20 (Invited Report)
- Cite as: Ryan Thomas, Report on arXiv:1901.08791v2, delivered 2019-03-20, doi: 10.21468/SciPost.Report.878
Report
The authors have satisfactorily addressed all of my comments and questions regarding their manuscript. In particular, section 2 (Concept and Design) is much clearer.
Aside from some grammar and spelling issues, some of which I have detailed in "requested changes", the only remaining comment I have is that their coils are not in the Helmholtz configuration. In the interest of precision, the authors should refrain from using this terminology. It appears only in the caption for Figure 3 and should be easy to remove this reference.
I recommend that this paper be accepted.
Requested changes
1) Remove the reference to "Helmholtz configuration" in the caption for Figure 3, as the coil pair is too far apart to be in the Helmholtz configuration.
2) Section 4, second paragraph: The discussion of the finite curvature is confusing. The sentence starting with "This finite curvature..." refers to the previous sentence about the axial curvature but then states that high-field seeking atoms will be confined along radial directions. The authors should be more precise about which curvature they are referring to, because high-field seeking atoms will indeed be trapped radially but they will be anti-trapped axially.
3) In the last sentence of the abstract, it should be "gas" and not "gases"
4) Section 1, paragraph 2: example is misspelled as "exemple"
5) Section 1, paragraph 2, last sentence: "limit" instead of "limits"
6) Section 2, equation 2: while the variable H is defined in the appendix, it is useful for it to be defined in the main text as well.
7) Section 3.2, paragraph 1: In the first sentence, the phrase "consists in the coil" should be "consists of the coil"
8) In the next sentence, it should be "cross-sectional area", not "cross section area"
9) Section 4.2, paragraph 1: In the last sentence, the value of the heating rate appears at the very top of page 8 and can be easily missed when reading. In terms of formatting, Figure 4 should be fixed at the top of the page so that this value is not missed.
10) Section 4.2, paragraph 2: In the second sentence, it should be "We observed that the temperature..." instead of "We observed that temperature".
Report #1 by Anonymous (Referee 2) on 2019-3-19 (Invited Report)
- Cite as: Anonymous, Report on arXiv:1901.08791v2, delivered 2019-03-19, doi: 10.21468/SciPost.Report.876
Report
I have read the updated manuscript and am happy that the authors have satisfactorily addressed all referee suggestions. I would recommend the paper be published as is.
I did pick up one minor typo in the caption of Fig 1, which should read "The copper coil consists of horizontally...".
Author: Jean-Philippe Brantut on 2019-03-21 [id 470]
(in reply to Report 1 on 2019-03-19)We thank the referee for his careful reading the revised manuscript. A new version has been submitted with the typo corrected.
Author: Jean-Philippe Brantut on 2019-03-21 [id 469]
(in reply to Report 2 by Ryan Thomas on 2019-03-20)We thank the referee for his careful reading of the updated manuscript. A revised version has been submitted, including the requested corrections. The description of the coils configuration as 'Helmholtz' has been removed to avoid possible confusions.