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arXiv:1309.5330 · Review of Scientific Instruments

Efficient continuous-duty Bitter-type electromagnets for cold atom experiments

Dylan O. Sabulsky, Colin Parker, Nathan Gemelke, Cheng Chin

Published Oct 1, 2013• 24 citations
arXivHTMLPDF

Abstract

We present the design, construction, and characterization of Bitter-type electromagnets which can generate high magnetic fields under continuous operation with efficient heat removal for cold atom experiments. The electromagnets are constructed from a stack of alternating layers consisting of copper arcs and insulating polyester spacers. Efficient cooling of the copper is achieved via parallel rectangular water cooling channels between copper layers with low resistance to flow; a high ratio of the water-cooled surface area to the volume of copper ensures a short length scale (~1 mm) to extract dissipated heat. High copper fraction per layer ensures high magnetic field generated per unit energy dissipated. The ensemble is highly scalable and compressed to create a watertight seal without epoxy. From our measurements, a peak field of 770 G is generated 14 mm away from a single electromagnet with a current of 400 A and a total power dissipation of 1.6 kW. With cooling water flowing at 3.8 l/min, the coil temperature only increases by 7 °C under continuous operation.

DOI
10.1063/1.4826498

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We present the design, construction, and characterization of Bitter-type electromagnets which can generate high magnetic fields under continuous operation with efficient heat removal for cold atom experiments. The electromagnets are constructed from a stack of alternating layers consisting of copper arcs and insulating polyester spacers. Efficient cooling of the copper is achieved via parallel rectangular water cooling channels between copper layers with low resistance to flow; a high ratio of the water-cooled surface area to the volume of copper ensures a short length scale (~1 mm) to extract dissipated heat. High copper fraction per layer ensures high magnetic field generated per unit energy dissipated. The ensemble is highly scalable and compressed to create a watertight seal without epoxy. From our measurements, a peak field of 770 G is generated 14 mm away from a single electromagnet with a current of 400 A and a total power dissipation of 1.6 kW. With cooling water flowing at 3.8 l/min, the coil temperature only increases by 7 °C under continuous operation.
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We present a modified Bitter-type electromagnet which features high magnetic field, fine electronic properties and efficient heat removal. The electromagnet is constructed from a stack of copper layers separated by mica layers that have the same shape. A distinctive design of cooling channels on the insulating layers and the parallel ducts between the layers ensures low resistance for cooling water to flow. A continuous current control system is also made to regulate the current through the electromagnet. In our experiment, versatile electromagnets are applied to generate magnetic field and gradient field. From our measurements, a peak magnetic field of 1000 G and a peak gradient field of 80 G/cm are generated in the center of the apparatuses which are 7 cm and 5 cm away from the edge of each electromagnet with a current of 230 A and 120 A, respectively. With the effective feedback design in the current control system and cooling water flow of 3.8 l/min, the stability of the current through the electromagnets can reach 10(-5).
We create a pair of symmetric Bitter-type electromagnet assemblies capable of producing multiple field configurations including uniform magnetic fields, spherical quadruple traps, or Ioffe–Pritchard magnetic bottles. Unlike other designs, our coil allows both radial and azimuthal cooling water flows by incorporating an innovative 3D-printed water distribution manifold. Combined with a double-coil geometry, such orthogonal flows permit stacking of non-concentric Bitter coils. We achieve a low thermal resistance of 4.2(1) °C kW−1 and high water flow rate of 10.0(3) l min−1 at a pressure of 190(10) kPa.
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 6 Li at 832.2\, 832.2 G. It offers a compact and cost-effective alternative solution for quantum gas experiments.
Many Zeeman slower magnets are geometrically captured by a vacuum chamber, preventing modification or repair without breaking the vacuum. We describe a Bitter-type electromagnet coil design that can be easily disassembled, reconfigured, repaired, and replaced without disturbing the vacuum system. This coil, designed to slow lithium atoms, produces a near-ideal field profile with a single DC power supply. With a resistance of 5.7(9) mΩ, an inductance of 8.8(2) μH, and switching times as low as ∼100μs, the coil compares favorably to other designs and can be disassembled, modified, and reassembled repeatedly without loss of performance. With forced-air cooling, the coil experiences moderate heating. This coil design offers greater flexibility than traditional electromagnet designs, and it can be retrofitted onto existing ultra-high vacuum chambers.
A pair of coils were made by hollow square copper wires with a rectangular transversal surface,which can be used to realize the trap for ultra-cold atoms and control of interaction among atoms by Feshbach resonance.We experimentally measured the magnetic field strength created by coils in Helmholtz and anti-Helmholtz configuration,and payed spcial attention to the factors such as spacing between two coils which influences the spatial distribution of magnetic field strength.At the same time,we calculated numerically the magnetic field strength in anti-Helmholtz configuration and presented the optimal value such as spacing when the uniformity of magnetic field strength was the best.With compari the measured and the simulated data,it is well-paralized with each other.Simultaneously working power of coils was calculated,as well as water speed and pressure for cooling coils.