Patent Description:
Electromagnetic coils are a basic component of a vast array of modern technologies. High-power electromagnetic coils in particular are used extensively in the fields of medicine, particle physics, micromanipulation, and many others. Such coils comprise electromagnetic coil windings that are often actively cooled with a fluid to allow the winding to withstand high current density without overheating.

Various strategies exist to make this cooling maximally effective. Generally speaking, it is advantageous to increase the rate of coolant flow and the area of the wire in contact with the coolant, while at the same time maximizing proximity of wire and coolant, i.e. any heat conducted to the coolant should have to traverse as short a distance through the wire as possible. Also, it is of course preferable to use standard wires and winding techniques if possible.

A number of designs and configurations for electromagnetic coil windings have been proposed in the literature, the most relevant of which are described here.

<CIT> describes a coil wound with two strips of material simultaneously - the first being an un-insulated conductor, and the second being a corrugated insulator - such that the corrugated insulating strip forms axial cooling channels in the coil structure.

<CIT> describes a transformer coil wound with two conductive strips, at least one of which is corrugated in order to form axially-extending coolant channels.

<CIT> describes an air-cooled transformer coil having spacer elements between winding layers that form axial passages for air to flow.

Many different approaches to create cooling channels by embedding different spacer elements within the winding are known. One example is <CIT> disclosing thermoplastic ducts spaced between the layers of conductive winding.

<CIT> describes a transformer coil having axial cooling ducts around which the coil wires are wound.

<CIT> describes a transformer having winding sections separated by axial spacer elements, thus forming radial cooling channels.

<CIT> describes an electromagnetic coil formed with a wire having shallow groove-shaped cutouts that form axial cooling channels.

<CIT> discloses an electro-magnetic coil according to the preamble of claim <NUM>.

The electro-magnetic coils described in the prior art require complex wire geometries and/or winding techniques.

In light of the aforementioned prior art and the limitations thereof, it is inter alia an object of this invention to provide a coil whose coolant permeability emerges intrinsically.

An electro-magnetic coil with coolant permeability according to the invention is wound using insulated wire, comprising a plurality of radially arranged layers and a plurality of axially arranged turns of the insulated wire per layer, wherein the insulated wire has a plurality of sections along its length with different cross-sections for any pair of two adjacent sections such that the empty spaces formed by the axially- and radially-adjacent cross-sections of insulated wire collectively form coolant channels.

A coil according to the invention comprises a coil whose coolant permeability emerges intrinsically as a result of the wire's varying cross-sectional shape. The difference of the cross-section of adjacent section can comprise a variation of height or a variation of width or a variation of both dimensions. Such an embodiment according to the invention is characterized by combined axial and radial cooling channels providing a coil winding with coolant permeability in both the axial and radial directions.

Such a coolant permeable coil can be formed from standard, readily available insulated wires using common coil winding techniques.

A coil can be wound from a wire having periodically varying cross-sectional shape and/or area along its length. This wire can be formed by drawing a standard insulated wire with uniform cross-section through a forming tool, which periodically compresses sections of the wire along its height, width or both. As the wire is wound in multiple rows over multiple layers, the varying cross-sections form coolant channels in both axial and radial directions. The shape and periodicity of the cross-sections can be optimized for various purposes. For instance, if it was advantageous for the majority of coolant to flow in the radial direction, the cross-sectional parameters of the wire could be adjusted to form primarily radial coolant channels, and vice versa.

The coil according to the invention results in a large heat transfer area with coolant distributed throughout the winding volume. It does not require separate spacer elements which simplifies the winding process and allows maximal packing density (volume copper / total volume) to achieve maximum magnetic field generation per given input power. The optimization is related to both the coil itself and the method of winding it. The fact that it does not require spacers and can be wound using standard practices is related to the method, but the realization of optimal packing density is a property of the winding configuration itself, regardless of how it is actually achieved.

The coil preferably comprises a housing with at least one inlet and at least one outlet, connected to gaps in axial and/or radial directions of the coil creating channels for a coolant fluid, wherein the inlet(s) and outlet(s) are adapted to be connected to a coolant circuit to pump a coolant fluid through the channels of the coil to cool the coil.

The inlet(s) and outlet(s) can be provided in longitudinal direction at opposite sides of the housing of the coil, e.g. at the same radial direction from the core of the coil, wherein the coolant is moved through the winding in axial direction by applying an axial pressure gradient and the radial cooling channels are used to distribute flow evenly over radial flow cross-section.

The inlet(s) and outlet(s) can also be provided in different radial distances from the core of the coil, then the coolant is moved through the winding in radial direction (inward or outward) by applying a radial pressure gradient and the axial cooling channels are used to distribute flow evenly over axial flow cross-section.

According to another embodiment, a relationship between the wire parameters and the resulting coil is defined beforehand that ensure the channels will continue to align with themselves over multiple layers, in order to realize an ideal channel configuration. One such relationship comprises in its simplest form to set L = <NUM>*pi*t, where L is the length of the periodic pattern, and t is the maximum thickness (height) of the wire, with pi being Ludolph's number. At the same time the circumference of the core on which the wire is wound is chosen to be a multiple of length L so that deformed and un-deformed sections between windings in the same layer align. In other words L is a divisor of the value of the circumference of the core on which the wire is wound. This alignment is still essentially achieved for a high number of layers increasing the diameter of the wound wire layers.

The coolant channels can be formed from the group encompassing radial coolant channels between subsequent layers of wires, axial coolant channels between adjacent turns of wires, and cross-section coolant channels between two adjacent turns and between two subsequent layers.

The cross-section of the wire can change between undeformed circular sections and two different deformed section, i.e. oval or elliptic sections with the longer axis direction in either layer or turn orientation. the wire using a wire-forming tool consisting in one embodiment of two wheels that have profiled surfaces corresponding to the desired wire thickness.

This method allows winding a coil from a single, continuous, insulated wire in traditional manner, but without requiring the use of additional spacing elements. The deformation process of an ordinary insulated wire takes place at the same time as winding by pressing and deforming the wire right before winding it.

According to one embodiment, the parameters of the wire taken from the group including thickness, deformation periodicity, deformed section length, deformed section width and inner diameter of the winding are chosen at random. This allows creating coolant channels which form stochastically. While the resultant channels will still be very effective, they will likely not be optimal.

The cross-section of the wire can change between undeformed circular sections and two different deformed section, i.e. oval or elliptic sections with the longer axis direction in either layer or turn orientation.

An electromagnetic coil winding according to the invention has intrinsically emerging radial and axial coolant channels. The coil is wound from a wire with varying cross-sectional shape, said wire consisting of alternating deformed and undeformed sections that collectively form into axial and radial coolant channels as the wire is wound around a core.

<FIG> show a first embodiment <NUM> of a wire <NUM> with varying cross-section in a top view, side view and perspective view, respectively. In fact, it shows a delimited portion of the wire, depicting the alternating deformed and un-deformed sections of the wire.

<FIG> shows at the same time the result of an embodiment of a method according to the invention. The wire <NUM> is initially a commercially available insulated wire. At first the wire's <NUM> cross-section is uniform throughout its length. The cross-section of the wire and its insulation, seen as one entity, can be square as shown with the wire <NUM> in <FIG>. The cross-section can also be rounded and especially a circle. As the wire <NUM> is wound onto the magnet core forming a coil, it is passed through a forming tool <NUM> as shown in <FIG>, periodically deforming sections of the wire <NUM> such that untouched areas <NUM> having the original cross-section (e.g. square or circular or a minimally deformed cross-section) alternate with deformed areas <NUM> having a new cross-section. The forming tool <NUM> will be described later on in connection with <FIG> showing one embodiment how to create a deformed wire <NUM>.

The initial wire <NUM> can be rectangular or oblong/elliptical, especially it can be an initial wire which is insulated. The cross-section of the deformed section <NUM> of <FIG> as well as of <FIG> is flatter and wider than the original section <NUM>. Between the sections <NUM> and <NUM> are present deformed upper shoulders <NUM> and side shoulders <NUM>, mainly comprising inclined surfaces between the corresponding adjacent surfaces. Adjacent shoulders <NUM> and <NUM> have opposite oriented inclinations. In case of a rounded wire <NUM> (not shown in the drawings), the shoulders are more complex tridimensional curves.

Of course it is possible to start with a wire <NUM> having a rectangular cross-section and deform it into an essentially square one. The deformation process is not intended to damage the insulation. It is possible that the main part of the deformation is exerted within the insulation coating.

<FIG> show a second embodiment <NUM> of a wire with varying cross-section in a top view, a side view and a perspective view, respectively. The wire <NUM> is a commercially available insulated wire. At first the wire <NUM>'s cross-section is uniform throughout its length. As the wire <NUM> is wound onto the magnet core, it is periodically deformed such that untouched areas <NUM> having substantially the original cross-section alternate with deformed areas <NUM> having a new cross-section. The cross-section of the deformed section <NUM> is both flatter and narrower than the original section <NUM>, i.e. it is compressed to a smaller cross-section area. In other words, the tool used to deform the wire <NUM> deforms the wire <NUM> along both its height and width.

Between the sections <NUM> and <NUM> are present deformed upper shoulders <NUM> and side shoulders <NUM>, mainly comprising inclined surfaces between the corresponding adjacent surfaces. Adjacent shoulders <NUM> and <NUM> have an inclination directed into the same direction, i.e. reducing the cross-sectional area from a section <NUM> to a section <NUM> and increasing the cross-sectional area from section <NUM> to section <NUM>.

<FIG> is a side view of a portion of one layer of a wire embodiment <NUM> where wire <NUM> is wrapped around a cylindrical magnet core <NUM>. It is clear that axial channels <NUM> will be formed between the wire <NUM> and the core's <NUM> surface, as well as between subsequent winding layers (not shown in <FIG>). Similar channels will also be formed, if an embodiment according to <FIG> is provided with the wire <NUM> of <FIG>.

<FIG> is a top view on a portion of four adjacent windings or turns <NUM> of one layer <NUM> of a coil formed from the wire <NUM> of the wire embodiment <NUM> depicted in <FIG>, wherein the wire parameters in connection with the core (not shown) are chosen such that the deformed sections <NUM> in adjacent windings are aligned. Of course, the undeformed sections <NUM> are then aligned as well. The deformed sections <NUM> are aligned with each other, forming clearly defined radial coolant channels <NUM>, whereas the side surfaces of the adjacent undeformed sections <NUM> are touching one the other at contact surfaces <NUM>.

When a second layer of windings (here four turns <NUM>) is arranged on the first layer <NUM> shown in <FIG>, then further contact surfaces <NUM> are built on the top surfaces of the undeformed sections <NUM>, if the alignment is chosen that the deformed section <NUM> of the subsequent layer is positioned with its longer portion of the cross-section as bottom surface on said top surface.

<FIG> is a perspective view of the four aligned windings <NUM> of one single layer <NUM> of <FIG>, wherein both axial coolant channels <NUM> and radial coolant channels <NUM> are visible.

<FIG> is a perspective view of portions of four adjacent windings <NUM> of one layer <NUM> of a coil formed from the wire depicted in <FIG>, wherein the adjacent deformed sections <NUM> are not aligned. In this case, of course, the undeformed sections <NUM> are not aligned as well in adjacent layers. Still, it is clear that both axial <NUM> and radial <NUM> coolant channels will emerge.

<FIG> is a top view of a 4x4 portion of a coil with four adjacent windings <NUM> in four layers <NUM> formed from the wire embodiment <NUM> depicted in <FIG> wherein the alignment of coolant channels <NUM> and <NUM> is not controlled and <FIG> is a cross-sectional view of the 4x4 portion of <FIG> showing that the channels <NUM> and <NUM> are allowed to form stochastically, since the alignment of the deformed sections <NUM> of the wire <NUM> is entirely random. The 4x4 array is chosen to illustrate the emerging cooling channels <NUM> and <NUM>. In a typical application both the actual number of windings per layer and as well as the actual number of layers can be many times larger, e.g. especially between <NUM> and <NUM> layers <NUM> with between <NUM> and <NUM> windings or turns <NUM>. The use of a <NUM> times <NUM> array of windings and layers has been chosen to illustrate the applying principles, it could be understood to show a detail of a larger coil.

<FIG> is a perspective view of a 4x4 portion of a coil formed from the wire embodiment <NUM> depicted in <FIG> wherein four adjacent windings <NUM> are aligned, forming well-defined coolant channels in both the axial and radial directions. The alignment within the array of wires of adjacent windings is controlled such that the deformed sections <NUM> align throughout winding layers <NUM>. The channels in both the radial and axial directions are clearly marked with reference numerals <NUM> and <NUM>, respectively. The hatched surfaces are representing the deformed surface of the smaller dimension.

<FIG> is a schematic cross-sectional view of a first embodiment of an electromagnetic coil <NUM> having a permeable winding <NUM> wherein the coolant flow is primarily axial as represented through the arrows with the reference numerals <NUM>. The first magnet embodiment <NUM> has a permeable winding <NUM> wound around a magnet core <NUM>. Winding <NUM> is shown as filling up the room between core <NUM>, end caps <NUM>, <NUM> as well as outer tube <NUM>; but of course, winding <NUM> is built from a plurality of wire windings in a plurality of wire layers as shown in <FIG> with wires <NUM> or <NUM> from <FIG> or <FIG> or similar embodiments.

End caps <NUM> and <NUM> form the structural support for the winding, and together with outer tube <NUM> form a sealed volume around winding <NUM>. Coolant is pumped as represented by inlet flow <NUM> through inlet(s) <NUM> in the endcap <NUM> and out through outlet(s) <NUM> in the endcap <NUM> as outlet flow <NUM>. As the coolant enters the winding, it disperses radially and flows axially as axial flow <NUM> to outlet <NUM>. Variations of the design are possible such as where inlet <NUM> and outlet <NUM> are on the same side of the magnet <NUM> by either segmenting the wire volume to form a U-shaped flow path that returns to the inlet side or by embedding flow channels to lead the coolant back to the inlet side at endcap <NUM> either through the core <NUM> or around the winding.

<FIG> is a schematic cross-sectional view of a further embodiment of an electromagnetic coil <NUM> having a permeable winding wherein the coolant flow <NUM> is primarily radial. The second magnet embodiment <NUM> comprises a permeable winding <NUM> wound around a magnet core <NUM>. Endcaps <NUM> and <NUM>, together with outer tube <NUM> form a sealed volume around winding <NUM>. Winding <NUM> shown as plain surface between elements <NUM>, <NUM>, <NUM> and <NUM> is as in <FIG> built from a plurality of wire windings in a plurality of layers. Coolant is pumped through inlet(s) <NUM> and through radial cooling channels <NUM>' in core <NUM>. As the coolant leaves the core <NUM> and enters the winding <NUM>, it disperses axially and flows radially into groove(s) <NUM> which are cut into outer tube <NUM> and which lead in a redirected axial coolant flow <NUM> to outlet(s) <NUM> in end cap <NUM>.

<FIG> is a schematic perspective view of parts of a wire forming apparatus, <FIG> is a schematic side-view of the forming wheels305 and <NUM> of the apparatus of <FIG> with a wire, and <FIG> is a schematic enlarged view of <FIG>. In an embodiment, the winding tool <NUM> as shown in the schematic perspective view of the main parts in <FIG> comprises a set of two forming wheels <NUM> and <NUM> having a pattern of ridges <NUM> on their outer surface. The initial preferably insulated wire <NUM> may be drawn through the forming wheels <NUM> and <NUM> passively or the wheels may be driven actively by means of a drive shaft <NUM>. As the wire <NUM> passes through the forming wheels <NUM> and <NUM>, its cross-section is periodically deformed by the ridges <NUM> on the wheels <NUM> and <NUM>. A synchronization mechanism presented here as two meshing gears <NUM> ensures that the forming wheels <NUM> and <NUM> rotate together and do not become out of sync. One of the meshing gears <NUM> is mounted on the driving shaft <NUM> whereas the second of the meshing gears <NUM> is mounted on an upper axle302. The forming wheels <NUM> and <NUM> are mounted in parallel onto these axles <NUM> and <NUM>, respectively.

<FIG> is a perspective view on a portion of a third embodiment of the wire <NUM>, depicting the alternating deformed and un-deformed portions of the wire <NUM>. The wire <NUM> has a round circular form in the undeformed wire portions <NUM>. The deformed wire portions <NUM> are delimited in the drawing of <FIG> by a line indicating a gradually rounded recess without an edge.

<FIG> is a cross sectional view on a 5x12 portion of a coil with five adjacent windings or turns <NUM> in twelve layers <NUM> formed from the wire <NUM> depicted in <FIG> wherein the alignment of coolant channels <NUM> and <NUM> is only controlled over the different layers. Reference numerals <NUM> in <FIG> indicate towards three different wires <NUM>; one wire <NUM> with a round circular cross section (indicated with a crosshair) and two oval or elliptic wires <NUM> having the largest diameter in two directions one perpendicular to the other. Arrow <NUM> indicate the adjacent turns, here five turns <NUM>. There are twelve layers <NUM>. In the embodiment of <FIG> every subsequent layer is directly contacting the more inner layer so that there are no axial coolant channels <NUM>. However, there are a plurality of radial coolant channels <NUM>. In view of the round wires <NUM> changing their cross-section from circular to elliptic or oval in the two perpendicular directions, there appear cross-section coolant channels <NUM> at the intersection of two adjacent turns <NUM> of wires <NUM> of two adjacent layers <NUM>. The number of adjacent turns <NUM> can be chosen in all embodiments from several to <NUM> or more The number of adjacent layers <NUM> can be chosen in all embodiments from several to <NUM> or <NUM> or more, creating arrays of e.g. <NUM> times <NUM> wires <NUM> (or wires <NUM> or wires <NUM>).

Finally, <FIG> is a perspective view of a 3x5 portion of a coil formed from the wire <NUM> depicted in <FIG> wherein adjacent windings are aligned, forming well-defined axial coolant channels <NUM> and cross-section coolant channels <NUM>. In other words, here, the adjacent windings of wires <NUM> in turns <NUM> are touching each other, but between different layers there appear axial coolant channels <NUM>. In any case, in view of the round wires <NUM> there are cross-section coolant channels <NUM> at the intersections.

Claim 1:
An electro-magnetic coil (<NUM>, <NUM>, <NUM>) with coolant permeability wound using insulated wire (<NUM>, <NUM>), comprising a plurality of radially arranged layers (<NUM>) and a plurality of axially arranged turns (<NUM>) of the insulated wire (<NUM>, <NUM>) per layer (<NUM>), characterized in that the insulated wire (<NUM>, <NUM>) has a plurality of sections (<NUM>, <NUM>; <NUM>, <NUM>) along its length with different cross-sections for any pair of two adjacent sections (<NUM> to <NUM>; <NUM> to <NUM>) such that the empty spaces formed by the axially- and radially-adjacent cross-sections of insulated wire collectively form coolant channels (<NUM>, <NUM>, <NUM>).