In this manuscript, the authors present a new design for a pair of electromagnets for quantum gas studies. Their design minimizes the amount of space occupied by the magnets and maximizes the amount of heat removed by water cooling. Since the maximum magnetic field that can be achieved is proportional to the square root of the dissipated power, this means that they can achieve large magnetic fields ($\sim$1000 G) at a distance of 43 mm from the centres of their coils. The authors describe the manufacture of their electromagnet and the water cooling considerations that they undertook to optimize their design. In their results, they show the magnetic field (as G/A) for a single coil, and they present measurements of the heat management of the electromagnet. These measurements are comparable to other modern designs of electromagnets for ultracold atomic physics with the added advantage of a compact design.
In general, I think that this manuscript will be of the most interest to experimentalists who are either setting up a new experiment or investigating improvements to an existing apparatus. In particular, the authors' descriptions of how the electromagnet was manufactured and assembled are detailed enough to allow someone else to build a similar device and to avoid pitfalls that the authors clearly encountered. The authors' measurements make a clear case that their design is effective at managing heat for reasonable pressure heads. Although their design was necessitated by the limited space into which they could put their magnets, a similar design methodology could be used for ultracold atom systems that use small, rectangular 'science cells' for their experiments. In such a situation, the improved heat management would be an asset, although other systems (such as in Ref 7) might be a better option. One measurement which is not reported but would be of interest to other experimentalists is the frequency response of the coils. As the authors do not report this, it seems that they are unconcerned with the dynamical response, but others who wish to implement this design may want an estimate of how fast the field can be changed.
I have two main concerns with the manuscript. The first is that their explanation of their design considerations is unclear. Equation 1, which is used to calculate the top-to-bottom temperature gradient on the coil, is presented without a reference or derivation. Equation 2 is similarly presented with little explanation, and I find its purpose vague and unclear. On a similar note, the authors include a photograph of the top surface of their coil to showcase its surface quality. It is, however, unclear why this is important. Would a roughly cut top surface significantly degrade the heat management?
My second concern is that the discussion of the magnetic field generated by the coil is limited. For instance, the authors state that a pair of coils is to be used for generating homogeneous fields at the location of their sample of atoms; however, the arrangement of this pair of coils is not stated. Is it supposed to be in a Helmholtz configuration? What is the homogeneity of the axial field at the location of the atoms? How fast can the magnetic field be changed: i.e., what is the dynamical response of the coils? How much does the magnetic field change with changes in the temperature of the coil?
As a last comment: this manuscript would benefit from further proofreading, as some of the phrasing and grammar negatively impacts the clarity of the article.
Overall, I think that this manuscript is of sufficient interest to those in the field of ultracold atomic physics, and to those outside, to be published in SciPost Physics.