Abstract:
An electromagnet coil comprising Litz wire windings and power leads without break or interruption is cooled by a perfluorinated liquid by sensible and phase change heat transfer in a closed system. The electromagnet coil may be housed in a pentagonal or hexagonal pressure vessel to allow high packing densities in an array or helmet configuration. The helmet is then lowered over a human cranium for transcranial electromagnetic stimulation. The Litz wire windings reduce the power and voltages required for operation, yet allow production of over 2 T of accurately directed magnetic pulses for direct nerve or neuron stimulation. The perfluorinated liquid maintains the temperature of the helmet to less than 35-40° C., ensuring a comfortable temperature device for a human test subject. A utility cable connects the helmet to an external cooling unit and an external power supply.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This invention was made with Government support under Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of Energy. The Government has certain rights in this invention. 
     
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention pertains generally to the cooling of high power electromagnets, and more particularly to the cooling and packaging of high power pulsed electromagnets for electromagnetic field induction in biological axons and ganglions. 
         [0005]    2. Incorporation by Reference 
         [0006]    Each of the following documents which is referred to herein using numbers inside square brackets (e.g., [1]) are incorporated herein by reference in its entirety: 
         [0007]    1. A theoretical calculation of the electric field induced in the cortex during magnetic stimulation. Electroencephalography and clinical Neurophysiologyl8:47 56. Rudin D O and Eisenman G. (1954). 
         [0008]    2. A model for the polarization of neurons by extrinsically applied electric fields. Biophysical Journal 50:1139 1156. Wada J, Rasmussen T. (1960). 
         [0009]    3. Suppression of visual perception by magnetic coil stimulation of human occipital cortex. EEGCNP 74:458 462. Artola A, Brocher S, Singer W. (1990). 
         [0010]    4. Slow magnetic stimulation of prefrontal cortex in depression and schizophrenia. Progress in Neuro-Psychopharmacology and Biological Psychiatry 21:105 110. Gerloff C, Corwell B, Chen R, Hallett M, Cohen L G (1997). 
         [0011]    5. Stimulus intensity and coil characteristics influence the efficacy of rTMS to suppress cortical excitability. Clinical Neurophsiology 117 2292-2301. Lang N, Harms J, Weyh T, Lemon R, Paulus W, Rothwell J, Hatwig S. (2006). 
         [0012]    6. Product Manual, 1987, Fluorinert Electronic Liquids, Commercial Chemical Products Division, 3M Company, St. Paul, Minn. 
         [0013]    7. Pool Boiling of High-Frequency Conductors. American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD; 2001; v.369, no.2, p.91-98. 
         [0014]    Conference: ASME International Mechanical Engineering Congress and Exposition. Wright S, Konecni S, Ammerman C, Sims J. (2001). 
         [0015]    8. Multiphase Cooling of High Frequency Conductors Encased in a Porous Medium. Proceedings of the ASME Summer Heat Transfer Conference; Publication HT2003-47492, 2003; v.2003, p.687-699. Morgan N, Ammerman C, Sims J, Konecni S, Wilson J. (2003). 
         [0016]    9. Coil assemblies for magnetic stimulators, U.S. Pat. No. 6,179,770; Jan. 30, 2001, Stephen Mould. 
         [0017]    10. Method and apparatus for magnetically stimulating neurons, U.S. Pat. No. 4,940,453; Jul. 10,1990, John A. Cadwell. 
         [0018]    11. Magnetic stimulator with skullcap-shaped coil, U.S. Pat. No. 5,116,304; May 26,1992, John A. Cadwell. 
         [0019]    12. Apparatus and methods for delivery of transcranial magnetic stimulation, U.S. Pat. No. 7,087,008; Aug. 8, 2006, Peter Fox. 
         [0020]    3. Description of Related Art 
         [0021]    Transcranial magnetic stimulation (TMS) is the use of trains of directed, magnetic field pulses to stimulate and affect brain and nerve function by means of the induced electric fields produced within brain and nerve tissue by rapidly changing magnetic fields [1,2]. The magnetic and electrical properties of the scalp, skull, cerebral fluid, brain, nerve and other body tissues permit the relatively efficient transmission of pulsed magnetic fields into the interior of the head, trunk and limbs by means of pulsed electromagnetic coils located outside of the body. Research indicates that magnetic stimulation may be used to enhance, degrade and measure/gage mental and nervous functions 
         [0022]    [3]. Further, there are indications that magnetic stimulation may have clinical and therapeutic value in the treatment of schizophrenia, depression and other mental illnesses [4]. It has been proposed that arrays of these coils be used to stimulate different areas of the brain simultaneously for both research and clinical purposes. These arrays would be made in the form of a helmet or shell around the head or panels for use against other parts of the body. There may be further highly speculative uses of the transcranial magnetic stimulation effect for purposes of enhancement or degradation of mental performance and direct stimulation input to the brain or nervous system elsewhere in the body. Pulsed magnet coils currently in use for TMS are large (90 mm in span across diameters or larger), and are solidly impregnated and hence cooled by solid conduction to the coil housing which is then air cooled.[5] To generate the required effect, a rapidly rising, high level magnetic field must be generated and projected by the coil. Generating this field using traditional methods requires a high electrical voltage (9 kV) to drive the coil. Attempts to actively cool the TMS coils using water based or dielectric oil coolants have been frustrated by both dangers to the test subjects (due to potential electrical shock hazards and high temperatures due to poor cooling) and inefficiency of heat transfer media (such as insulating oils that would not undergo phase change during normal operation, and hence had only low heat capacity). There is also a sharp report or noise when the coils are energized which can confuse the evaluation of the effect of magnetic stimulation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0023]    An aspect of the invention is a fluid cooled electromagnet that comprises: an electromagnet that has a central region; and a means for cooling the electromagnet. The means for cooling the electromagnet may comprise a refrigerant that is forced through the electromagnet, wherein the refrigerant is substantially a dielectric. The refrigerant may be substantially comprised of Fluorinert™ FC-87™, which has a boiling point of about 30° C., or about 86° F. 
         [0024]    The means for cooling the electromagnet may comprise: a housing, where the housing comprises: an inlet that flows an externally cooled refrigerant to the central region; an outlet that receives refrigerant that has flowed through the electromagnet; and an electrically non-conducting pressure vessel that entirely encloses the electromagnet, that opens to the inlet and outlet. Here, the pressure vessel does not substantially affect a magnetic field generated by the electromagnet when energized. Additionally, the pressure vessel has sufficient strength to contain a pressure of the refrigerant comprising: an inlet pressure as the refrigerant enters the inlet; a phase change pressure, generated as the refrigerant undergoes a phase change from liquid to gas through boiling heat transfer; and an outlet backpressure as the refrigerant flows through the outlet. 
         [0025]    Another aspect of the invention is that the fluid cooled electromagnet is wound with a Litz wire to form an electromagnet coil winding. The electromagnet coil winding may be supported by a frame, and may also comprise multiple layers. The electromagnet coil winding may also comprise multiple turns. 
         [0026]    The fluid cooled electromagnet may also comprise: a current source I in  comprised of the Litz wire of which the electromagnet is wound; and a current sink I out  comprised of the Litz wire of which the electromagnet is wound. The current source I in , current sink I out , and the electromagnet coil winding may consist of the same uninterrupted continuous Litz wire without any splice, joint, or other means for attaching. 
         [0027]    The fluid cooled electromagnet may be one of an array of fluid cooled electromagnets that can programmably direct magnetic fields into a human cranium. The fluid cooled electromagnet may also direct magnetic fields into nerves. 
         [0028]    The fluid cooled electromagnet may comprise: a non-ferromagnetic core. Here, the non-ferromagnetic core may be an “air core”. Alternatively, the fluid cooled electromagnet may comprise: a ferromagnetic core. The ferromagnetic core ferromagnetic core is preferred for lower frequency operation as the skin depth at these frequencies better matches the physical dimensions of the core, as the core may magnetically respond sufficiently and rapidly through its thickness due a match between dimensions of the core and skin depth at the operating frequency to effect enhancement of the magnetic field being produced, and may also be adequately cooled in such an arrangement. 
         [0029]    A still further aspect of the invention is a method for transcranial magnetic stimulation that comprises: providing an electromagnet coil; flowing a dielectric refrigerant over the electromagnetic coil to cool the electromagnetic coil; and directing a magnetic pulse from the electromagnet coil to a human or other mammalian cranium. Here, the dielectric refrigerant may most preferably be a perfluorocarbon. The directing of the magnetic pulse from the electromagnet coil to the human cranium step may effect transcranial magnetic stimulation. 
         [0030]    In another embodiment of the invention, a transcranial magnetic stimulator may comprise: an electromagnet wound of a Litz wire; a set of power leads that connect to the electromagnet comprised of the same Litz wire without splice or interruption; and a perfluorocarbon in contact with the Litz wire for substantially the entire length of the Litz wire; whereby the Litz wire is cooled by the perfluorocarbon when the electromagnet is energized. Here, the transcranial magnetic stimulator may comprise: an external cooling unit that cools the perfluorocarbon that is heated due to heat dissipated by the Litz wire and ferromagnetic core when the electromagnet is energized. The external cooling unit may be a closed system that prevents loss of the perfluorocarbon 
         [0031]    The transcranial magnetic stimulator may also comprise: a computer controlled power supply that energizes the electromagnet with a waveform directed by a computer control, wherein: the electromagnet may continuously produce an external directed magnetic field in excess of 2 T without thermally induced damage. 
         [0032]    Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0033]    The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only: 
           [0034]      FIG. 1A  is a cross sectional perspective view of a high power, high duty cycle pulsed electromagnet for nerve or transcranial magnetic field stimulation showing refrigerant cooling paths through the electromagnet coil windings. 
           [0035]      FIG. 1B  is a cross sectional perspective view of the device of  FIG. 1A , showing in detail the I in  and I out  and coil winding wiring. 
           [0036]      FIG. 1C  is a perspective view of a frame used in the device of  FIG. 1A  for forming and supporting the electromagnet coil winding. 
           [0037]      FIG. 2  is a perspective drawing of one potential application of the high power, high duty cycle pulsed electromagnet for transcranial magnetic field stimulation. 
           [0038]      FIG. 3A  is a cross-sectional view of a single concentric power and cooling cable. 
           [0039]      FIG. 3B  is a cross-sectional view of a coextruded parallel power and cooling cable. 
           [0040]      FIG. 3C  is a cross section of a simplified Litz wire with bare individual conductors. 
           [0041]      FIG. 3D  is a cross section of a simplified Litz wire comprised of individual strands of conductor that are coated with an insulator. 
           [0042]      FIG. 3E  is a cross section of one embodiment of the utility cable shown in detail. 
           [0043]      FIG. 4  is a top view of a prior art figure-of-eight transcranial magnetic stimulation coil. During operation, the figure-of-eight coil would be positioned over the scalp. This device has no provision for active cooling. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Definitions 
       [0044]    The following definitions are provided to facilitate an understanding of the terminology used herein. It is intended that those terms not present in these Definitions be given their plain meaning as understood by those persons having ordinary skill in the art. 
         [0045]    Fluorinert™ means the trademarked brand name for the line of electronics coolant liquids sold commercially by 3M. It is an electrically insulating, inert perfluorocarbon fluid which is used in various cooling applications but is mainly for cooling electronics. Different molecular formulations are available with a variety of boiling points, allowing it to be used in “single phase” applications where it remains a fluid, or for “two-phase” applications where the liquid boils to remove additional heat via evaporative cooling. An example of one of the formulations 3M uses would be for instance, FC-72, or perfluorohexane (C 6 F 14 ) which is used for low temperature heat transfer applications due to its boiling point of 56° C. Another example is FC-75, perfluoro(2-butyl-tetrahydrofurane). 
         [0046]    FC-87 means a specific 3M product of Fluorinert with a boiling point of about 30° C. This product contains perfluorocarbons comprising C 5 -C 18 . 
         [0047]    Litz wire is a shortened form of Litzendraht wire, which is a bundle of multiple insulated and appropriately positioned strands that has lower ac resistance than a single strand of the same cross sectional area. This is due to the reduction of the skin effect (i.e. the current of an ac signal doesn&#39;t penetrate all the way into a conductor), but is limited by the mutual coupling between the strands. High frequency currents are known to flow substantially on the surface, resulting from the “skin” effect. Thus, a single thick conductor flowing a high frequency current results in much of the wire not being used, as the current flows only on the skin, or outermost surface. The limitation of mutual coupling is reduced by appropriately positioning or weaving the strands so that each individual strand occupies every possible position in the bundle periodically along the length of the bundle. The positioning or weaving equalizes flux linkages and hence reactances causing the current to divide more uniformly between strands. 
       Description 
       [0048]    Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus generally shown in  FIG. 1A  through  FIG. 4 . It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein. 
         [0049]    Refer now to  FIG. 1A , a pulsed, high field, high duty cycle, cooled electromagnet coil  100  for transcranial and nerve magnetic stimulation. An outer circumference pressure vessel  102  necks down  104  to a smaller diameter outflow tube  106 . A frame  108  is disposed within the pressure vessel  102 . The frame  108  has a base  110 , and a plurality of apertures  112 . Litz wire  114  is wound within the frame  108 . The electromagnet coil  100  may comprise a spiral wound pancake or helically wound multiple layer and multiple turn pulsed electromagnetic, non-ferromagnetic core (“air core”) coil of copper or silver (or other high electrical conductivity metals) Litz wire  114  conductor (a typical Litz wire would be New England Wire Technologies copper filament 3×35/36). An inner fluid supply line  116  may be disposed within the larger diameter outflow tube  106  or alternatively the may be two separate or coextruded parallel tubes (shown later in  FIGS. 3A and 3B ). The inner fluid supply line  116  may have a land  118  within which an O-ring  120  or other suitable gasket seals to an upper frame  122 . Externally cooled refrigerant  124  flows down the inner fluid supply line  116 , and ultimately forms radial flow lines  126  that enter the plurality of apertures  112  found in the frames  108 . The radial flow lines  126  flow through the frames  108  and around the Litz wire  114 , whereby the Litz wire  114  is cooled by the forced refrigerant flow to result in a warmed, mixed phase refrigerant exhaust flow  128 . The exhaust flow  128  exits between the outflow tube  106  and the exterior diameter of the inner fluid supply line  116 . A layer  130  of Litz wire  114  may be wound on a frame  108 . A second such layer  132  is a method of increasing field strength of the electromagnet coil  100 . An additional layer  134  may be repeated as needed to provide the necessary projected magnetic field strength  136 . 
         [0050]    Pressure vessel  102  has been shown in  FIG. 1A  as radially symmetric about its center, but the pressure vessel may instead take on a hexagonal or pentagonal geometry as desired for increased ability to closely pack electromagnet coils  100  adjacently (in very close proximity, or even touching) with little loss of space. 
         [0051]    The polygon shaped (such as hexagonal and pentagonal) tapered coil housing shape permits a large number of coils to be arranged about the head for better resolution and precision of magnetic field generation. The interior corners of the vertices of the hexagonal and pentagonal housings provide room for coil power leads and return flow of coolant while allowing the coils to be arranged in dense patterns. The small size of the coils in the present invention will also enable the construction of arrays of coils compact enough for a subject or patient to wear within medical imaging machines. It is also projected that the fluid coolant and construction used in the present invention will provide some damping or muffling of the acoustic coil noise generated when the coil is operated. 
         [0052]    The arrangement of externally cooled refrigerant  124  flowing from the electromagnet coil  100  bore and then through a combination of radial apertures  112  and circumferential paths through and around the winding layers  130 ,  132 ,  134  causes the coolest of the externally cooled refrigerant  124  to make initial contact with the hotter section of Litz wire  114  at the smallest diameter of the electromagnet coil  100 . In high field, rapidly pulsed coils, heat production is a strong function of the background magnetic field level experienced by an individual turn of wire; the turns at the center of the coil are exposed to the highest magnetic fields. 
         [0053]    The Litz wire  114  is supported and located by the frame  108 , which may be made of a non-metallic, insulating material and cooled with a forced flow of dielectric, perfluorinated, low boiling point (˜30 degrees C.), liquid refrigerant such as Fluorinert FC-87™ [6,7]. The forced coolant flow is directed in a radial outward and circumferential manner through the windings by means of patterns of holes and slots  112  in the frame  108 . Warmed coolant (liquid and vapor phase) is exhausted  128  on the radius of the coil and returned to a central condenser via the utility or power cable as later shown in  FIG. 2 . Other electromagnet coil  100  coolant flow patterns are also envisioned depending upon coil winding details to achieve consistent cooling of the Litz wire  114  during its entire operating length. 
         [0054]    Refer now to  FIG. 1B , where more details of the electromagnet coil  100  are shown. Here, the Litz wire input conductor I in    138  enters the coil winding  140  at an outer perimeter  142 . Inner layer crossovers  144  and  146  continue the windings of frames  108  between layers  130 - 132  and between layers  132 - 134 . The Litz wire output conductor I out    148  exits the coil winding  140  at another outer perimeter  150 . The power leads are placed on the outer diameter of the coil to reserve the coil bore for coolant flow to the coil turns at the center and to reduce magnetic loading on the power leads. The power leads I in    138  and I out    148  are also made from Litz wire and are a continuation of the coil winding (there are no splices) and pass back through a utility power cable to the pulsed power source (shown later in  FIG. 2 ). 
         [0055]    While the electromagnet coil  100  is shown with nothing but refrigerant in the center in FIG.  1 A&#39;s “air core” case, for low frequency pulsed operation a ferromagnetic core  152  may be used in the center of the coil winding  140  to make an “iron core” implementation. In the iron core implementation, the ferromagnetic core  152  is cooled by the externally cooled refrigerant  124 . In higher frequency usage, the ferromagnetic core  152  may have channels and other apertures permitting increased cooling by the forced flow of the externally cooled refrigerant  124 . 
         [0056]    Refer now to  FIG. 1C , which is a perspective view of a single frame  108  without any Litz wire ( 114 ) being shown for clarity. The frame  108  is basically disk shaped about the base  110 , with an inner diameter  152  and an outer diameter  154 . Between the inner diameter  152  and the outer diameter  154  is a support wall  156  that is between about ½ and ¾ of the thickness of the Litz wire (not shown  114 ), so as to provide lateral retention to the Litz wire (not shown  114 ) when energized with heavy currents. The support wall  156  spirals in from the outer diameter  154  to the inner diameter  152 , thereby providing continuous support of the Litz wire (not shown  114 ) as it enters from the outer diameter  154  and exits from the inner diameter  152 . Alternating layers  130 , 132 , and  134  of frames  108  will be wrapped in the same sense so that a magnetic field  136  {right arrow over (B)} is projected out from the electromagnet coil  100  (both shown in  FIG. 1A ). The support wall  156  spirals here are shown as so large as to only allow three windings. This has only been done for clarity, and any number of windings may be used as desired with the support wall  156  spirals adjusted appropriately. 
         [0057]    Each frame  108  is constructed of a dielectric material that maintains sufficient mechanical strength to support the electromagnet coil  100  during high repetition, high current operation, while being cooled by the externally cooled refrigerant  124 . Most likely, the frame  108  would most economically be made by injection molding of an appropriate thermoplastic, such as polycarbonate, acrylonitrile butadiene styrene (ABS), HDPE, or nylon. If the electromagnetic coil  100  is to see continuous high repetition rate operation, then it may be preferable to use polytetrafluoroethylene due to its very low dissipation factor. These materials would likely have sufficient dielectric properties in this application, so long as no carbon fibers were added as an admixture in the process of their molding. 
         [0058]    Refer now to  FIG. 2 , which is a drawing of one potential application of the high power, high duty cycle pulsed electromagnet  100  for nerve or transcranial magnetic field stimulation  200 . In this drawing, a subject  202  has placed over their head a helmet  204  comprising an array of individual hexagonal and pentagonal electromagnetic coils  100 . Here, within the helmet  204 , and not shown, are various bundling and routing arrangements of power lines for each individual electromagnet coil  100 , as well as a combination of the cool refrigerant  206  and the warmed exhaust refrigerant  208 . Cooling unit  210  provides for cooling the warmed exhaust refrigerant  208  and converting it once again into cool refrigerant  206 . Power supply  212  provides a plurality of individual connections to each of the electromagnet coils  100 . 
         [0059]    Umbilical junction  214  separates from a combination utility cable  216  the cool refrigerant  206 , the warmed exhaust refrigerant  208 , and the two Litz wire conductors (I in    138  and I out    148  of  FIG. 1B ) each electromagnet coil  100  in the array helmet  204 . Separated Litz wires pass as bundles  218  and  220  (or more, as needed) to the computer controlled (not shown) power supply  212 . 
         [0060]    The utility cable  216  is made of nested and bundled co-extruded flexible polymer tubing with several independent and isolated passageways to provide support, electrical isolation and cooling of power leads, and passage and isolation of cooled refrigerant  206  and warmed exhaust refrigerant  208 . The electromagnet coil  100  has been designed to produce a small (30 mm diameter), high field (2 Tesla at the coil projection face), high duty cycle high frequency, long service life (1000 hours), safely cooled, modular pulsed electromagnet coil that may be arranged in compact, efficient spherical or shell like and planar or curved panel arrays or as shown in  FIG. 2  a helmet  204  configuration. 
         [0061]    Refer now to  FIG. 3A , which is a cross-sectional view of a single power and cooling cable  300  that is comprised of components seen previously in  FIGS. 1A and 1B . An inner fluid supply line  116 , where the high voltage power lead I in    138  is also contained, may be disposed within the larger diameter outflow tube  106 . Externally cooled refrigerant  124  flows (•—out of the figure) through the inner fluid supply line  116 . A warmed, mixed phase refrigerant exhaust flow  128  exits (x—into the figure) between the interior diameter of the outflow tube  106  and the exterior diameter of the inner fluid supply line  116 , where the high voltage power lead I out    148  is also contained. 
         [0062]    Refer now to  FIG. 3B , which is a cross-sectional view of a coextruded parallel power and cooling cable  302 . An externally cooled input fluid supply line  304  may be disposed parallel to an outflow tube  306 . Externally cooled refrigerant  124  flows (•—out of the figure) through the externally cooled input fluid supply line  304 . A warmed, mixed phase refrigerant exhaust flow  128  exits (x—into the figure) through the outflow tube  306 . High voltage power lead I in    138  passes through the interior of input fluid supply line  304  where it is cooled by single phase liquid refrigerant. High voltage lead I out    148  passes through the interior of the outflow tube  306 , where it is cooled by the mixed phase refrigerant exhaust flow  128 .′ 
         [0063]    Refer now to  FIG. 3C , which is a cross section of a simplified Litz wire  114 . Here, bare individual conductors  308  comprise the Litz wire  114 . This is one form of Litz wire  114 , however, not a preferred form. 
         [0064]    Refer now to  FIG. 3D , which is a cross section of a simplified Litz wire  114 . Here, the Litz wire  114  is comprised of individual strands of conductor  310  that are coated with an insulator  312 . This insulator  312  permits improved high frequency performance of the Litz wire  114 . 
         [0065]    It should be noted that in both  FIGS. 3C and 3D  that only seven conductor strands were used simply for clarity. In actuality, the Litz wires may be comprised of 10&#39;s to even 100 strands. The Litz wire  114  described earlier in this patent was comprised of 35 strands. 
         [0066]    Refer now to  FIG. 3E , which is a cross section of one embodiment of the utility cable  216 , shown in detail. Here, the utility cable  216  begins with a relatively large diameter utility outflow tube  312 , which may be further coated on its outer diameter with polyimide or other insulation coating  314 . An inner utility fluid supply line  316  which may be further coated on its outer diameter with polyimide or other insulation coating  314 , and may be disposed within the relatively larger diameter utility outflow tube  312 . Externally cooled utility refrigerant  320  flows (•—out of the figure) through the inner utility fluid supply line  316 . A warmed, mixed phase refrigerant utility exhaust flow  322  exits (x—into the figure) between the interior diameter of the utility outflow tube  312  and the exterior diameter of the inner utility fluid supply line  316 , where one lead each of high voltage leads pairs  324 ,  326 , and  328  are also contained. The other leads of high voltage lead set pairs  324 ,  326  and  328  are contained in the interior of inner utility supply line  316 . These three sets of high voltage power lead pairs  324 ,  326 , and  328  provide power connections to three of the electromagnet coils  100  previously shown in  FIG. 1A . 
       Advantages 
       [0067]    Magnetic transcranial stimulation depends on the electrical effect of a rapidly changing magnetic field 
         [0000]    
       
         
           
             
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         [0000]    within the brain. There is a requirement to precisely direct these fields. Further there is need to generate trains of tailored, rapidly rising combined pulses on a continuing basis and move the magnetic field maximums of these combined pulses rapidly to different parts of the brain. This invention provides for small coils (relative to 90 mm pancakes in present use) capable of safely producing high fields, and that can be mounted in a closely arranged array around the head or in a compact panel. The small size of the coils decreases inductance, which permits greater values of 
         [0000]    
       
         
           
             
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         [0000]    at lower voltages that consequently reduces energy requirements. The use of appropriately sized and textured non-impregnated or bonded (supported in a passageway with adequate open cross-section for coolant flow) Litz wire for windings significantly reduces eddy current and other high frequency losses. The use of perfluorinated Fluorinert FC-87 enables efficient low temperature (near human or mammal body temperatures) cooling with an inert, safe, non-electrical conducting fluid through a combination of sensible heat increase and phase change (boiling). 
         [0068]    Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. 
         [0069]    Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”