Abstract: A superconducting coil protective system comprises a quenching detector (QD) for detecting occurrence of a quenching in a superconducting coil (L) and generating a quenching signal indicative of the occurrence of the quenching. In response to the quenching signal, a voltage controller (VC) reduces an output voltage from a power source (PS) to zero or to a negative polarity. A current interrupter (CI) including a circuit breaker (CB) or a fuse (F) is connected in parallel to the superconducting coil (L) for allowing a first commutation of a current from the superconducting coil (L) to the current interrupter (CI) upon the reduction of the output voltage from the power source (PS). The system also comprises a protective resistor (RD) connected in parallel to the current interrupter (CI) for allowing a second commutation of the first-commutated current thereto upon the opening of the current interrupter (CI), whereby energy of the second-commutated current is dissipated in the protective resistor.

Abstract: A contact maker-breaker is disclosed in which the power contacts are associated in series with a superconducting element which is controlled by a heating element and which is structured so as to have a very high resistance following its controlled transition from the superconducting state to the normal state in response to a closing or opening order or following its intrinsic transition from the superconducting state to the normal state in response to a fault current, so that closing and opening of the power contacts takes place on the same leak current of a very low value.

Abstract: A hybrid current limiter comprising a first winding of non-superconducting conductive material having a large number of turns and electrically connected in series with a superconductoring coil of low self-inductance and placed in a cryostat, and a second winding of non-superconducting conductive material having a small number of turns, said second winding being closely coupled with said first winding in such a manner as to obtain low overall inductance, the second winding being connected in parallel with the series circuit constituted by the first winding and the superconducting coil.

Abstract: A modular superconducting magnetic energy storage (SMES) inductor includes a plurality of vertically adjacent winding modules each comprising a number of serially connected concentric solenoid coils. Pairs of adjacent winding modules are connected in series to form paired winding modules each of which occupies a compartment in a sectioned dewar. Only a single shorting switch is provided for each winding module for use during an emergency dump of cryogenic fluid from the dewar. Adjacent paired winding modules can be connected in series by a single connector penetrating sectional plates between dewar compartments. Arrangements of bypass switches provide the capability of taking either a single winding module or a pair of winding modules out of service while the remaining winding modules and pairs of winding modules remain in service.

Abstract: The invention relates to a circuit breaker for limiting a direct current and comprising a combination of first means including superconducting windings for limiting the current and second means for interrupting the residual current. The invention is applicable to interrupting high tension direct currents.

Abstract: A quench detector for a superconducting coil is provided which utilizes an optical coupling and a rotary encoder. The presence of a resistive voltage in the superconducting coil created by a quench will cause a rotatable readout coil to move. Movement of the readout coil will be detected by light passing through or reflected by an optical encoder, which will interrupt or transmit light passing from one or more light sources towards one or more light sensors. Preferred embodiments utilize optic fibers for the light sources and sensors, which are unaffected by the high magnetic fields or hostile environment of the superconductor coil.

Abstract: A power switching system for controlling the conductivity of a plurality of thyristors of the gate turn-off type (GTOs) which are connected in parallel between two power sources by gradually introducing a time compensation to force the times of turn-off of each of the thyristors toward matched values by determining the turn-off time during each conduction cycle and thereafter advancing or retarding the turn-off signal for the following conduction cycle to correct for the difference in turn-off times. A difference signal is generated between time of turn-off of an average current of the thyristors and the time of turn-off of an individual current in one of the thyristors from which a time advance or delay signal is added to the thyristor turn-off signal in response to the current flowing in a capacitor type integrator. This allows the turn-off times to reach a perfect match during periods in which the current is the same for several cycles.

Abstract: An electric power generating device includes a bundle of conductors which are placed in a magnetic field generated by north and south pole pieces of a permanent magnet. The magnetic field is shifted back and forth through the bundle of conductors by a pair of thin films of superconductive material. One of the thin films is placed in the superconducting state while the other thin film is in a non-superconducting state. As the states are cyclically reversed between the two films, the magnetic field is deflected according to the Meissner effect back and forth through the bundle of conductors to produce an electromagnetic force.

Abstract: The present invention provides a passive superconducting sensor for quench detection in a superconducting coil. The sensor consists of a first circuit electrically connected to two voltage taps of a superconducting coil. The first circuit uses nonsuperconducting components and preferably contains a resistive element. The first circuit is magnetically coupled to a second circuit by a hybrid transformer. The second circuit is superconducting and contains a readout coil and preferably a second hybrid transformer. The second hybrid transformer is magnetically coupled to a sense coil which detects flux changes in the superconducting coil. The readout coil is coupled to a readout device which measures changes in the current through the readout coil. The current in the readout coil can be made a function only of the resistance of the superconducting coil between the voltage turns and thus can be used to detect a quench.

Abstract: A superconducting magnet apparatus comprising a superconducting main coil (1) for generating a uniform magnetic field and at least one superconducting shim coil (2a, 2b) electromagnetically coupled to the superconducting main coil (1) for increasing the uniformity of the magnetic field generated by the main coil (1). An emergency run down main coil heater element (21) is disposed adjacent to the main coil (1) for demagnetizing the latter, an emergency run down shim coil heater element (22a, 22b) is disposed in proximity of the shim coil (22a, 22b) for demagnetizing the latter, and a heater power source (24) is provided for supplying an electrical power to the heater elements (21,22a,22b). A switching unit (25,26,27) is connected between the heater elements (21,22a, 22b) and the heater power source (24) for connecting the heater power source (24) to the shim coil heater element (22a, 22b) and to the main coil heater element ( 21) at different time points with a predetermined time interval therebetween.

Abstract: A self-shielding system of closed superconducting circuits shields a specific volume from changes in an external magnetic field in which the circuits are located; the configuration of circuits is chosen so that induced currents in the circuits, arising from magnetic flux conservation for each closed circuit, tend to cancel any change in the external magnetic field. In another aspect, a single closed self-shielding superconducting circuit comprised of more than two circular loops connected in series shields a specific volume from changes in an external magnetic field in which the circuit is located; the configuration of the circuit is chosen so that induced currents in the circuit, arising from magnetic flux conservation for the circuit, tends to cancel any change in the external magnetic field.

Abstract: Apparatus for generating a magnetic field includes a superconducting coil winding and a conducting, non-magnetic electrical field member in proximity to and insulated from the winding. The winding is energized by a direct-current source, reaching a predetermined electrical potential when in the superconducting state. The electrical field member is held at a positive potential relative to the winding and the electrical field between the field member and the turns of the winding enables the winding to remain superconductive at current magnitudes exceeding the critical value that would have existed in the absence of such electrical field.

Abstract: An electrical resistance device which comprises a resistance element and a superconducting gate element electrically connected in series therewith. The normal state resistance of the superconducting gate element is substantially greater than the resistance of the resistance element. A plurality of such devices can be used with the windings of a superconducting magnet, for example, to protect the windings thereof if the temperature of a particular winding region rises rapidly (the winding region quenches) due to operational instabilities, for example. At a quench the voltage at the winding region being quenched is applied to all the other devices at the other windings to generate heat at such devices in response to a relatively small voltage increase at the initially quenched region. Each of the other winding regions is thereby quenched and the gate elements thereof are triggered into their normal resistive states so that the current in the devices is reduced to a safe level.

Abstract: A magnetic field compensating apparatus having a plurality of compensating units comprising a plurality of serial coils each of which is disposed concentrically along the main magnetic field and symmetrically with regard to a plane perpendicular to the main magnetic field and a plurality of power sources which separately supply currents to these compensating units, and made in such a manner that a plurality of error magnetic field components are generated by each of the compensating units, a compensating magnetic field is obtained by the whole of a plurality of the compensating units, and each of the currents supplied to the compensating units is decided in accordance with a constitution of a corresponding compensating unit.

Abstract: An actively shielded, superconducting magnet of a nuclear magnetic resonance tomography apparatus has an inner coil system and an outer coil system connected in series to avoid an increase in the external field upon the quench of one of the coil systems. To avoid losing the protection of the shielding effect from external magnetic field disturbances, a superconducting current limiter having a low critical current-carrying capability is connected in the coil system to guide a difference current between the inner coil system and the outer coil system. To avoid an unwanted increase in the external field in the event of a quench of one of the coil systems, the current limiter becomes normally conductive in the presence of a current difference larger than a prescribed value.

Abstract: A CMOS circuit including a variable conductor means interposed between a power supply and the CMOS circuit. The CMOS circuit comprises a P channel MOS FET and an N channel MOS FET laterally formed on the surface of a semiconductor substrate, inherently producing a parasitic thyristor which can be latched-up with destructive consequences under certain circumstances. The variable conductor means, interposed between the power supply and CMOS circuit, preferably includes a superconductor arranged to sharply switch to a normal conductor mode when the current level exceeds a critical current level, established to be less than the latch-up holding current of the parasitic thyristor, thereby to prevent latch-up.

Abstract: A current limiter comprising a cryostat provided with a first insulating feedthrough for an inlet conductor and a second insulating feedthrough for an outlet conductor, and a conductor running from one feedthrough to the other inside the tank, said conductor being constituted at least in part by a superconducting material, the cryostat being filled with a fluid at a temperature which is low enough to maintain said material in the superconducting state, said portion made of superconducting material including at least one portion comprising superconducting wires (7, 8) wound in opposite direction windings on two coaxial insulating formers (14, 15). Respective the ends of each of the superconducting wires (7, 8) are connected firstly to the inlet conductor and secondly to the outlet conductor via identical elementary current feeds (21A, 22A).

Abstract: A superconducting switching device having no moving components for reversing current flow through a load. This load typically is a superconducting magnet and, in this application, the present invention also selectively serves as a persistent switch. The invention includes a pair of switching units connected between the load (magnet) and a current source. These switching units each have a pair of superconductor members and a mechanism for selectively producing in the switching units either a substantial electrical resistance or no resistance. Through the use of a control logic, the level of resistance of the switching units can be changed to effect the direction of current flow. In the case of the superconductor magnet, both switch units can be simultaneously made to have substantially zero resistance, and their interconnection forms the persistent switch for the superconducting magnet.

Abstract: The circuit monitors the superconducting state of a superconducting magnet winding. The winding is subdivided into two serially connected sub-windings with an intermediate tap point. The end of the sub-windings are connected via an electrically conducting parallel branch. This parallel branch consists of two serially connected sub-branches, each containing at least one ohmic resistor. There is a junction between the sub-branches. This junction and the tap point of the magnet winding are the diagonal points of a bridge circuit, to which is connected an electronic device for evaluating and processing the voltage signal to be measured. To account for the ohmic resistances associated with the sub-windings of the superconducting magnet winding and thereby increasing the sensitivity of the circuit, each sub-branch of parallel branch contains at least one capacitor.

Abstract: A power operated contact apparatus extends and retracts one or more electrical leads into and out of a cryostat for making and breaking, at a cryogenic temperature, electrical contacts with a superconductive circuit. A pair of rigid elongated leads extend into a cold space of the cryostat which is at or near a cryogenic temperature. A connector is fixed at the inner end of each lead for making electrical contact in the cold space with a mating connector of the superconductive circuit. A guide journals each lead for axial movement and seals against the leading using an elastomeric O-ring coated with a lubricious polymer. A foundation is attached and sealed to the cryostat and to the guide means so that the connector on the inner end of the lead is extendable into making electrical contact with the connector of the superconductive circuit in the cold space.

Abstract: A superconducting electromagnet apparatus wherein a superconducting main coil and a superconducting shield coil for reducing external magnetic field leakage generated by the main coil are magnetically, but not electrically, coupled, a single magnetizing power source is connected across the main coil, and persistent currect switches are respectively connected in parallel with the main coil and the shield coil.

Abstract: A superconducting electromagnet apparatus wherein a superconducting main coil and a superconducting shield coil for reducing external magnetic field leakage from the main coil are connected in series, a magnetizing power source is connected across the series connection assembly, and persistent current switches are respectively connected in parallel with the main coil and the shield coil.

Abstract: A uniform magnetic field coil assembly having a plurality of pairs of coil elements each included in circuit comprising the parallel connection of a permanent current switch and its protecting means and an individual exciting power source, wherein the plurality of pairs of coil elements are symmetrically disposed against a plane perpendicular to the central axis of the uniform magnetic field coil assembly in the longitudinal direction and the plurality of pairs of coil elements are connected in series, thereby regulating the current flowing to each of the plurality of pairs of coil assembly elements for forming the uniform magnetic field coil as predetermined.

Abstract: A quench propagation device for a superconducting magnet having at least one pair of superconducting coils operates so that in the event of a transition to normal-conductance (quench) of a first coil of the coil pair, which up to that point was superconducting, the second coil of this pair is also converted from the superconducting operating state to the normal-conducting state using heating arrangements thermally connected to the coils. This device is constructed so that in the event of a quench rapid magnet de-excitation and uniform current distribution and, consequently force relationships, are achieved. The heating arrangements include two auxiliary windings magnetically closely coupled with their particular assigned coils of the coil pair. The auxiliary winding material is a discrete normal-conducting conductor having a predetermined specific electrical resistance.

Abstract: A superconducting magnet apparatus comprises a superconducting coil, a persistent current switch with a small current bearing capacity, and a protective element respectively connected in parallel with the superconducting coil and an emergency run down unit including a heater circuit having a heater power source, a heater element disposed in proximity to the superconducting coil, and a heater circuit switch connected in series with the heater element. Thus, the heater element is energized and warmed to bring at least a part of the superconducting coil into a normal state.

Abstract: A circuit is provided comprising a plurality of series connected superconductive coils. Each of a plurality of series connected shunt resistors is connected in parallel with at least one corresponding series connected superconductive coil. A superconductive switch, which includes a length of superconductive wire, is connected in parallel with the series connected superconductive coils. The switch further includes a first and second heater means which are thermally coupled to the superconductive wire. The first heater means is connectable to an external power supply. The second heater means has a plurality of different sections with each of the shunt resistors connected in parallel to one of the sections so that a quench in any of the superconductive coils causes a section of the second heater means to warm and drive the superconductive switch normal.

Abstract: A superconducting magnet apparatus comprises an emergency run down unit having a heater power source and a heater circuit switch, a superconducting coil, and a persistent current switch circuit, the persistent current switch connected in parallel to the superconducting coil and including a first persistent current switch connected in parallel to a first protective element of low resistance and a second persistent current switch connected in parallel to a second protective element of high resistance. The second persistent current switch has a persistent switch-heater connected to the heater power source through the heater circuit switch. Thus, when it becomes necessary to demagnetize the superconducting magnet apparatus being operated in a persistent current mode, the second persistent current switch parallel to the second protective element of high resistance is opened, whereby current flowing through the superconducting magnet decays rapidly.

Abstract: A superconducting system including a superconductive coil and a perpetual current switch connected in parallel therewith in a cryogenic vessel, wherein the perpetual current switch includes a superconductive lead and a heater that causes the superconductive lead to be normal-conductive; and a DC power source that can arbitrarily change the output thereof with respect to the superconductive coil and the perpetual current switch. The system circulates a current of a specified amount within a closed loop constituted by the superconductive coil and the superconductive lead so as to create a perpetual current loop.

Abstract: A high gradient magnet is disclosed having a coil of superconducting material immersed in liquid helium in a toroidal shaped liquid helium vessel, supported in axial spaced concentric relation to a toroidal shaped liquid nitrogen vessel which forms one end of a toroidal heat shield made of high heat conductive material in which the liquid helium chamber is supported by a first coil support ring and a second coil support ring. The heat shield and liquid helium chamber are in turn supported in a toroidal shaped vacuum chamber which is in turn supported in a heavy iron cylindrical enclosure closed at the ends and having an opening through the center of its ends. A slurry containing iron particles may pass through the opening in the center whereby the iron particles from the slurry are retained by a matrix. The first coil support ring has two ends supported on the vacuum vessel and an intermediate part.

Abstract: A superconductive magnet has a main coil for creating a primary magnetic field and a plurality of shim coils for correcting aberrations in different gradients in the primary field. The shim coils are also connected in shunt with shim quench heaters and with superconductors which together with the shim coils form a plurality of persistent loops. A plurality of protective heaters are electrically connected to the main coil and are thermally connected to the superconductors. When quenching begins in the main coil, current is diverted through the protective heaters causing them to heat. This increases the temperature of the superconductors in the persistent loops causing them to switch from the superconductive to the resistive state and divert current into the shim quench heaters. These heaters in turn heat the shim coils and drive the shim coils resistive to safety dissipate any energy therein.

Abstract: A superconducting magnet system includes a cryostat having a cold shield, a superconducting magnet coil disposed in the cold shield, a two-stage cryogenerator connected to the magnet coil for cooling the magnet coil to an operating temperature substantially between 10 and 13K, and a flux pump connected to the magnet coil for feeding current to the magnet coil, the flux pump including a transformer having primary and secondary windings and superconducting switches having conductors, and the magnet coil, windings and conductors being formed of superconducting material having a high critical temperature.

Abstract: A superconducting coil device in accordance with the present invention includes a cryostat formed by accommodating liquid helium, a superconducting coil which is accommodated in the cryostat along with liquid helium, a persistent current switch for short-circuiting the ends of the superconducting coil, and a thyristor connected to both ends of the persistent current switch. The gate electrode of the thyristor and the intermediate tap of the superconducting coil are connected via a resistor and/or diode. To both ends of the persistent current switch there are connected each of one end of leads that are formed by superconducting wire, and on the other ends of lead wires there are provided terminals. In addition, in the exterios of the cryostat there is provided a power supply for charging and discharging the superconducting coil by being connected selectively to that terminals.

Abstract: A wiring harness for a shielded superconducting magnetic resonance magnet in which resistors are connected in parallel with pairs of symmetrically connected coils. The symmetric nature of the magnetic field can be maintained during a quench since coils placed symmetrically about the plane of symmetry always conduct the same current, eliminating unbalance forces that are normally associated with a quench of a shielded magnet.

Abstract: The device is for a superconducting magnetic coil assembly that is to be cryogenically cooled by a liquid coolant, and is subdivided into several partial winding sections that are connected one after the other to protect the assembly in the event of an unintended transition from the superconducting state to the normal conducting state. A protective resistor is connected in parallel with each partial winding section and the ends of adjacent partial winding sections that face one another are connected to the corresponding ends of their respective protective resistors by a common section of an electrical conductor. With a passive protection device of this kind, it should be possible to use protective resistors with a relatively small mass. According to the invention, the protective resistors are located in the exhaust gas stream of the coolant, and in each of the sections of the conductor that are common to adjacent partial winding sections there is located a small auxiliary resistor.

Abstract: A magnetic field gradiometer includes a pair of coils, encompassing different regions of space. A SQUID is provided to detect a difference in flux linking the coils thereby to provide a measure of a magnetic field gradient between the coils. A control element of a superconducting material is provided in the vicinity of the coils and a heater is controlled to vary the proportion of the element assuming the superconducting state. By suitably varying this proportion the balance condition of the coils can be altered. The control element may operate in a feed back circuit. A coil subjects both coils to an alternating magnetic field at a preset frequency. A component in the output of the SQUID having this frequency is used to control the heater.

Abstract: An automatic current lead retraction system for superconducting magnet installations. An automatic current lead retraction system utilizes an operator wherein either hydraulic or pneumatic cylinders bring about electrical contact of the current leads or the separation thereof as well as a safety shorting switch for the system. By using the pneumatic or hydraulic cylinders and all non-magnetic materials, there is no influence upon the magnetic field created by the superconducting magnet. Provision is made to monitor the condition of the magnet to be certain that it is in a persistent mode before the current leads are retracted. Furthermore, safety signals are generated to assure that no current is flowing at the time of retraction, that the resistance across the contacts is sufficiently low when engaged and that all electrical, air/hydraulic fluid systems are functioning properly before operation of the retracting system. Overall control is achieved using a microprocessor.

Abstract: A method for operating magnet correction coils is provided through the control of correction coil currents. The currents are determined from field measurements through the use of an iterative weighting algorithm. The algorithm is iterative and adjusts the weights at each iteration so as to reduce the range of variation.

Abstract: A method and apparatus for making a fast transition of the entire superconducting winding of an electrical apparatus, which is arranged in a vacuum chamber and is cooled by a cryogenic medium, from the superconducting operating state into the normal-conducting state by heating the entire winding in case of a disturbance of a section of the winding which causes that section to become normal-conducting is disclosed. A predetermined quantity of a gas which is at a higher temperature and which would be frozen at the superconducting operating temperature is introduced into the vacuum chamber such that the superconducting parts of the winding are heated above the critical transition temperature characteristic for superconduction. The pressure in the spaces containing the cryogenic medium can also be increased by a predetermined value such that boiling of the cryogenic medium is suppressed when the superconducting parts are heated to at least the critical transition temperature.

Abstract: A winding for superconducting inductive apparatus having one or more sets of main and auxiliary superconducting windings connected in parallel, with the auxiliary winding being disposed in a field-free region of the main winding. The main and auxiliary windings are arranged such that the main winding carries substantially all of the normal operating current of the apparatus and the auxiliary winding, which is located in a field-free region, carries overload currents of the apparatus. The volume of the main windings may thus be reduced, reducing the hysteresis and eddy current losses of the apparatus during normal operation, while incorporating a built-in safety factor to withstand excessive overloads.

Abstract: A method of detecting and analyzing normal zones in a superconducting coil which involves generating a signal representative of the real power dissipated within the superconducting coil after the background noise and transient conditions within the coil have been accounted for. The power signal is integrated with respect to time to provide a signal proportional to the total energy dissipated within the superconductor which is then compared against a critical reference signal so that a quench signal is generated to immediately disconnect the superconducting coil when the reference signal is exceeded and to allow the coil to discharge its energy into an external device to prevent coil damage. An exemplary circuit for implementing the method is disclosed.

Abstract: Disclosed is a method for detecting propagating normal zones in a superconducting coil or magnet by monitoring the energy consumed by the magnet/coil per unit time and comparing that value with a previously recorded or stored value of energy consumed per unit time. The monitoring is done outside the cryostat and external quench detection circuitry configurations are disclosed for carrying out the method.

Abstract: A superconducting magnet arrangement having a sealed cryogenic environment utilizing liquid helium, a superconducting coil immersed in the liquid helium, a constant current power supply exterior of the cryogenic environment and connected to the coil by leads cooled by varying helium boil off and an electrical shunt connect across the magnet. Variations in the helium boil off are compensated by exposing the shunt to and cooling it by the same helium boil off or by exposing negative temperature coefficient device to such flow or by a combination of such methods.

Abstract: A superconducting transformer having a winding arrangement that provides for current limitation when subjected to a current transient as well as more efficient utilization of radial spacing and winding insulation. Structural innovations disclosed include compressed conical shaped winding layers and a resistive matrix to promote rapid switching of current between parallel windings.

Abstract: Disclosed is a magnetically latching solenoid including a pull-in coil and a delatching coil. Each of the coils is constructed with a combination of wire materials, including material of low temperature coefficient of resistivity to enable the solenoid to be operated at cryogenic temperatures while maintaining sufficient coil resistance. An armature is spring-biased toward a first position, that may extend beyond the field of force of a permanent magnet. When voltage is temporarily applied across the pull-in magnet, the induced electromagnetic forces overcomes the spring force and pulls the armature to a second position within the field of the permanent magnet, which latches the armature in the pulled-in position. Application of voltage across the delatching coil induces electromagnetic force which at least partially temporarily nullifies the field of the permanent magnet at the armature, thereby delatching the armature and allowing the spring to move the armature to the first position.

Abstract: Thermal isolation of a cryostat is improved for a superconducting solenoid having a plurality of separately energizable coils or winding sections by reducing the number of conductors required to selectively energize the persistence switch controlling a particular winding section. As a consequence, the dimensions of the vent and fill tube openings of the cryostat which accommodate these conductors may be reduced. In one embodiment a diode is incorporated in series with heating element of each switch. The switches are connected to form a steering network to control as many as p.ltoreq.n(n-1) separate coils using n conductors to actuate p persistence switches. In another embodiment n(n-1)/2 coils are similarly controlled with n conductors using the time-current response of persistence switches without diodes. Still another embodiment utilizes a binary to hexadecimal converter within the cryostat to permit n externally generated signal conductor to select as many as p.ltoreq.2.sup.n -1 persistence switches.

Abstract: This invention provides a rotating superconductor magnet for producing a rotating lobed magnetic field, comprising a cryostat; a superconducting magnet in the cryostat having a collar for producing a lobed magnetic field having oppositely directed adjacent field lines; rotatable support means for selectively rotating the superconductor magnet; and means for energizing the superconductor magnet.

Abstract: Method and equipment for transferring energy to or from a direct-current superconducting field coil to change the magnetic field generated by the coil in which a second direct-current superconducting coil is used as a storage coil, and energy transfer between the field coil and the storage coil is effected automatically in dependence upon a control programe. Preferably, the control programe acts upon a variable transformer which is coupled by respective rectifier/inverters to the field and storage coils and also serves for initial supply of energy to the coils.