Abstract: Embodiments of coolant guides for use in magnetron assemblies are provided herein. In some embodiments, a coolant guide for use in a magnetron assembly includes: a body having a guide channel extending through the body, wherein an upper opening of the guide channel corresponding with an upper surface of the body has a first size and a lower opening of the guide channel corresponding with a lower surface of the body has a second size greater than the first size, and wherein the body includes a first pair of outer sidewalls that are substantially parallel to each other and a second pair of outer sidewalls that are angled toward each other; and an upper lip extending away from an upper surface of the body.

Abstract: Apparatus for providing a magnetic field within a process chamber are provided herein. In some embodiments, an apparatus for providing a magnetic field within a process chamber includes: an inner rotating mechanism including a first plate having a central axis, wherein the first plate includes and a first plurality of magnets and is rotatable about the central axis; and an outer lifting mechanism including a ring disposed proximate the first plate, the ring having a second plurality of magnets coupled to a bottom surface of the ring proximate the peripheral edge of the ring, wherein the ring is movable in a direction perpendicular to the first plate.

Abstract: Embodiments of the present invention generally provide a magnetron that is encapsulated by a material that is tolerant of heat and water. In one embodiment, the entire magnetron is encapsulated. In another embodiment, the magnetron includes magnetic pole pieces, and the magnetic pole pieces are not covered by the encapsulating material.

Abstract: A magnetron has an anode cylinder, ten vanes, three strap rings. The ten vanes are fixed to an inner surface of the anode cylinder and arranged in a radial pattern of which center is at an axis of the anode cylinder. Each of the three strap rings connects vanes that are alternatively arranged. A first strap ring and a third strap ring are arranged on a first end of the vanes in a direction of axis, and a second strap ring is arranged on a second end that is opposite to the first end. Outer diameter of the second strap ring is equal to inner diameter of the first strap ring and outer diameter of the third strap ring is equal to inner diameter of the second strap ring.

Abstract: An apparatus for generating a hollow cathode arc discharge plasma, including two plasma sources, each including a hollow cathode and an electrode which is associated with the hollow cathode and which has an opening that extends through the electrode, wherein the hollow cathodes of the two plasma sources are connected to a pulse generator which generates a bipolar, medium-frequency pulsed voltage between the two hollow cathodes. Here, in each of the two plasma sources, the hollow cathode is connected in an electrically conducting manner, directly or with interconnection of at least one current direction limiting component, to the associated electrode.

Abstract: A modular magnetron for use in UV curing lamp assembly is disclosed. The modular magnetron includes a vacuum tube having a vacuum tube body, a top assembly, and a bottom assembly. The top assembly is configured to substantially overlay the vacuum tube. The bottom assembly is configured to substantially extend about the vacuum tube, the vacuum tube being positioned to partially protrude from the bottom assembly, the bottom assembly including a cooling assembly configured to employ a flexible clamp-type fitting about the vacuum tube body for substantially maintaining thermal and electrical conductivity. The top assembly is configured to be releasably fastened to the bottom assembly about the vacuum tube with removable fasteners.

Abstract: A magnetron assembly for a rotary target cathode comprises an elongated support structure, a magnet bar structure movably positioned below the support structure, and a plurality of drive modules coupled to the support structure. The drive modules each include a motorized actuation mechanism operatively coupled to the magnet bar structure. A controller and battery module is coupled to the support structure and is in operative communication with the drive modules. The controller and battery module includes an electronic controller and at least one rechargeable battery. The battery is configured to energize each motorized actuation mechanism and the electronic controller. One or more power generation modules is coupled to the support structure and in electrical communication with the battery, such that electrical energy output from the power generation modules recharges the battery.

Abstract: Embodiments of a lamp comprise a light source and an active cooling device that propagates airflow within the lamp to dissipate heat from the light source. In one embodiment, the lamp comprises a light emitting diode (LED) device and an inductor that couples in series with the light emitting diode (LED) device. The lamp also comprises a diaphragm magnetically coupled with the inductor, wherein the diaphragm can flex between a first position and a second position to generate the air flow.

Abstract: A magnetron includes an anode with an anode casing at least partly surrounding the anode. A pair of permanent magnets on each side of the anode define an interaction region and create a magnetic circuit defining a magnetic field through the interaction region. A mass of magnetically permeable material is positioned in a vicinity of the magnetic circuit. The mass is arranged to be slidable over the anode casing. A locking device secures the position of the mass to set the strength of the magnetic field through the interaction region.

Abstract: A THz reverse micromagnetron includes a MEMS-based reverse magnetron configuration in which the anode is located at the center of the magnetron surrounded by a cathode ring. Electrons move radially inward in the combined electric and magnetic cross-fields and can reach orbiting angular frequencies in the THz region, even with a magnetic field of the order of 1 T or less. The THz reverse micromagnetron is portable, operates at room temperature, and can be bright.

Abstract: A magnetic field generator arranged behind a target and for generating a magnetic field on a front surface of the target based on magnetic force lines can include a ring-shaped outer magnetic body having a pole axis in a parallel direction (X-direction) with respect to the target surface, a center magnetic body arranged on an inner side of the outer magnetic body and having a pole axis in a parallel direction (X-direction) with the direction of the pole axis of the outer magnetic body, a yoke plate for supporting the outer magnetic body and the center magnetic body from behind, and a magnetic permeable plate for changing a magnetic field distribution of the front surface of the target. The magnetic permeable plate is arranged so as to be supported by the yoke plate from behind.

Abstract: A electrodeless lamp including a fluorescent discharge vessel, a tip, an amalgam, a lamp core, and a heater. The vessel contains a gas having a partial vapor pressure and a fluorescent material. The tip has an inner end engaging the vessel, and an opening in communication with the gas. The amalgam is positioned within the opening, in heat transfer relation with the tip. When the temperature of the amalgam decreases, mercury vapor in the gas condensates onto the amalgam, causing a decrease in the partial vapor pressure of the gas. The opposite occurs when the amalgam temperature increases. The lamp core generates a magnetic flux, causing an electrical discharge in the gas. The heater includes a positive temperature coefficient connected to a winding of the lamp core. The heater is in heat transfer relation with the tip and heats the tip when the electrodeless lamp is in a dimming mode.

Abstract: A multi-column electron beam exposure apparatus includes: multiple column cells; an electron beam converging unit in which two annular permanent magnets and electromagnetic coils are surrounded by a ferromagnetic frame, the two annular permanent magnets being magnetized in an optical axis direction and symmetrical about the optical axis, where the electromagnetic coils adjust magnetic fields of the annular permanent magnets; and a substrate provided with circular apertures through which electron beams used in the column cells pass, respectively, where the electron beam converging unit is disposed in each of the circular apertures. The two annular permanent magnets may be disposed one above the other in the optical axis direction, and the electromagnetic coils may be provided inside or outside the annular permanent magnets in their radial direction.

Abstract: A microwave tube including: a) an electron gun capable of producing a beam of electrons in the form of a hollow axisymmetrical cylinder in repetitive operation; and b) a body in which the beam is intended to propagate, the body ending with a collector and being provided with means for applying an axial magnetic field for guiding the beam and, upstream from the collector, with a resonant structure crossed by the beam, intended to group the electrons into a succession of packets (P). The resonant structure is formed with two coupled cavities which follow along the axis (Z) of the beam, the coupling being achieved via an inter-cavity region crossed by the beam, this structure having axial symmetry the axis of which is that of the beam and being dimensioned so that the transformation of the electrons in packets is accomplished at a frequency which is that of the ? resonant mode of the resonant structure.

Abstract: A modular magnetron for use in UV curing lamp assembly is disclosed. The modular magnetron includes a vacuum tube having a vacuum tube body, a top assembly, and a bottom assembly. The top assembly is configured to substantially overlay the vacuum tube. The bottom assembly is configured to substantially extend about the vacuum tube, the vacuum tube being positioned to partially protrude from the bottom assembly, the bottom assembly including a cooling assembly configured to employ a flexible clamp-type fitting about the vacuum tube body for substantially maintaining thermal and electrical conductivity. The top assembly is configured to be releasably fastened to the bottom assembly about the vacuum tube with removable fasteners.

Abstract: The invention discloses a microwave supplying apparatus including a microwave generator, a first power divider, a second power divider, a first waveguide, and a second wave guide. The first waveguide is connected to the microwave generator and has a first output terminal and a second output terminal to divide a microwave generated by the microwave generator along a first direction. The second power divider is connected to the first output terminal and has a third output terminal and a fourth output terminal to divide the microwave along a second direction. The first waveguide and the second waveguide are connected to the third output terminal and the fourth terminal respectively and receive the microwave through the first power divider and the second power divider to respectively output the microwave fields with approximate intensity distributions.

Abstract: To provide a magnetron capable of reducing noises in a low frequency band of 30 MHz or less without deteriorating the stability of a load depending on phases, and also ensuring the precision of assembly dimensions without increasing the number of components, a coiled filament 3 is arranged between an input-side end hat 61 and an output-side end hat 7 which are supported by a cathode supporting rod 8. A larger-diameter boss 61a in the end hat 61 extends to the interior of an interaction space, a smaller-diameter boss 61b and one end 3a of the filament 3 are secured to each other, and the other end 3b is secured to a boss 7a of the end hat 7. Here, the dimension of an axial free length part F which forms an electron emission part which is not secured to the end hats 61 and 7 of the filament 3 is set to 50% or more and 80% or less of the axial dimension H of plate-like vanes 2, and the electron emission part is arranged so as to be displaced to the output side.

Abstract: A magnetron includes an anode with an anode casing at least partly surrounding the anode. A pair of permanent magnets on each side of the anode define an interaction region and create a magnetic circuit defining a magnetic field through the interaction region. A mass of magnetically permeable material is positioned in a vicinity of the magnetic circuit. The mass is arranged to be slidable over the anode casing. A locking device secures the position of the mass to set the strength of the magnetic field through the interaction region.

Abstract: In each anode vane 10, there is provided the brazing material spreading prevention groove 13 that interconnects the strap ring inserting portions 11 and 12 in parallel to the direction of the central axis Ax. With such a configuration, it is possible to prevent the residual brazing material 3a from spreading to the front end part 10a of the anode vane 10 when each anode vane 10 is brazed on the inner peripheral surface of the anode cylinder 1. Therefore, non-uniformity in thickness of the anode vanes 10 caused by the residual brazing material 3a is suppressed, and electrostatic capacity between the anode vanes 10 adjacent to each other becomes substantially constant. Thus, it is possible to obtain stable resonant frequency. In addition, it becomes easy to perform adjustment for obtaining the stable resonant frequency in that non-uniformity in initial frequency of the time when the magnetron is completely assembled decreases.

Abstract: The magnetron includes: a cylindrical-shaped anode barrel member 10 having two openings respectively formed in the two end portions thereof; a cathode structure member 12 disposed on the center axis of the anode barrel member 10; more than one anode vane 11 disposed radially through an action space 13 in the periphery of the cathode structure member 12 and fixedly mounted on the inner wall surface of the anode barrel member 10; and, a pair of funnel-shaped pole pieces 14 and 30 respectively disposed in their associated ones of the two openings formed in the two end portions of the anode barrel member 10, each pole piece including a small-diameter flat portion FL1 having a penetration hole formed in the central portion thereof, a large-diameter flat portion FL2 having a diameter larger than the diameter of the small-diameter flat portion FL1, and a conical-shaped slanting portion SL for connecting the large-diameter flat portion FL2 and small-diameter flat portion FL1 to each other.

Abstract: A gap is provided between a cooling block 22 and a magnetic yoke 20. A cushioning material 25 is interposed in the gap to fix the cooling block 22 relatively to the magnetic yoke 20 by screws. Thus, even when metals having a large difference in tendency of ionization are used in the cooling block 22 and the magnetic yoke 20, the corrosion of the metals hardly arises. Further, the cushioning material 25 is provided in the gap between the cooling block 22 and the magnetic yoke 20, so that an impact or vibration to an anode tubular member 10 can be mitigated and the disconnection and deficiency of the filament of a cathode structural member can be reduced. Further, since a dimensional unevenness of the cooling block 22 or the magnetic yoke 20 can be absorbed by the cushioning material 25, the dimensional accuracy of parts does not need to be improved to make an assembly easy.

Abstract: This disclosure is related to a magnetron including a pillar-shaped cathode having a center axis, an anode coaxially arranged with the cathode so as to be separated from the cathode via a predetermined space, and a pair of pole pieces provided to both ends of the cathode in the axial direction so as to oppose to each other and having opposing faces perpendicular to the axial direction. The pole piece has a first ridge of a ring shape that is formed on the opposing face and is coaxial with the cathode.

Abstract: A plasma lighting system having a thin metallic film resonator includes: an electrodeless bulb emitting light by making luminous material filled therein converted into plasma state; and a resonator housing the electrodeless bulb in an inner space, transmitting the light generated from the electrodeless bulb, and blocking the microwave generated from a microwave generator and applied to the inner space from being leaked out so that a resonance mode is provided to make the electrodeless bulb emit light, wherein the resonator is a thin metallic film resonator including a thin metallic film formed in a cylindrical shape and a supporting member extended along the inner peripheral surface of the thin metallic film so as to support the thin metallic film.

Abstract: A method and apparatus for producing a distributed plasma at atmospheric pressure. A distributed plasma can be produced at atmospheric pressure by using an inexpensive high frequency power source in communication with a waveguide having a plurality particularly configured couplers disposed therein. The plurality of particularly arranged couplers can be configured in the waveguide to enhance the electromagnetic field strength therein. The plurality of couplers have internal portions disposed inside the waveguide and spaced apart by a distance of ½ wavelength of the high frequency power source and external portions disposed outside the waveguide and spaced apart by a predetermined distance which is calculated to cause the electromagnetic fields in the external portions of adjacent couplers to couple and thereby further enhance the strength of the electromagnetic field in the waveguide. Plasma can be formed in plasma areas defined by gaps between electrodes disposed on the external portions.

Abstract: In each anode vane 10, there is provided the brazing material spreading prevention groove 13 that interconnects the strap ring inserting portions 11 and 12 in parallel to the direction of the central axis Ax. With such a configuration, it is possible to prevent the residual brazing material 3a from spreading to the front end part 10a of the anode vane 10 when each anode vane 10 is brazed on the inner peripheral surface of the anode cylinder 1. Therefore, non-uniformity in thickness of the anode vanes 10 caused by the residual brazing material 3a is suppressed, and electrostatic capacity between the anode vanes 10 adjacent to each other becomes substantially constant. Thus, it is possible to obtain stable resonant frequency. In addition, it becomes easy to perform adjustment for obtaining the stable resonant frequency in that non-uniformity in initial frequency of the time when the magnetron is completely assembled decreases.

Abstract: Disclosed herein is a magnetron. The magnetron comprises an anode cylinder, upper and lower magnets provided to upper and lower portions of the anode cylinder, and upper and lower magnetic poles connected to the magnets, respectively. Each of the magnets has an inner diameter of 19˜21 mm, a thickness of 11.5˜12.5 mm, and an outer diameter of 50˜54 mm.

Abstract: A magnetron 10 is equipped with a helical filament 39, as an element of a cathode assembly, arranged on a central axis of an anode cylindrical body 13. Assuming that a resistance value of the filament 39 before forming the carbonized layer is R1 and a resistance value of the filament 39 after forming the carbonized layer is R2, a thickness of the carbonized layer 42 of the filament 39 is determined such that a carbonization rate Rx defined by the equation “Rx={(R2?R1)/R1}×100” in a range of from 30 to 50%.

Abstract: In a magnetron 41, when a radius of a flat portion 45b of a pole piece 45 is Rp, a radius of the inner circumference of a large-diameter equalizing ring 51 is Rs2, Rp?Rs2, a radius of the outer circumference of a small-diameter equalizing ring is Rs1, a radius of a circle inscribed in a leading edge of an anode vane is Ra, and a minimum length between the pole pieces in the axial direction is Lg, the values of Ra, Rs1, Rs2, and Lg are set such that the following Expressions 1 and 2 are established: 1.85Ra?(Rs1+Rs2)/2?1.96Ra, and[Expression 1] 2.84Ra?Lg?3.0Ra.

Abstract: A pulse magnetron includes a cylindrical shell anode, a cathode provided at the center of the anode having a number of vanes mounted radially on an inner wall of the cylindrical anode shell, and a pair of pole pieces provided for applying a magnetic field to an interaction space where the outer side of the cathode is opposed to inner ends of the vanes. The anode and the cathode are arranged to satisfy at least either (i) increasing the radius of the inscribed circle defined by the inner ends of the vanes or (ii) decreasing the radius of the cathode surface as the magnetic flux density along the axial direction of the cathode at both ends of the inner end of the height of the vanes.

Abstract: A magnetron capable of being efficiently assembled is provided. The magnetron includes a filament, a pair of shields, a pair of leads, a pair of connection plates, and a pair of terminal rods. The filament is coil-shaped. The shields are attached to both ends of the filament, respectively. The leads are attached to the shields at first ends of the leads, respectively. The connection plates are attached to second ends of the leads, respectively. The terminal rods are attached to the connection plates, respectively, to supply power to the leads through the connection plates, and have slender protrusions, which have sectional areas smaller than sectional areas of attachment portions of the terminal rods so that the terminal rods are attached to the connection plates with the slender protrusions passing through the connection plates.

Abstract: Anode with a 2450 MHz resonance frequency, and magnetron therewith, the anode including a cylindrical anode body with an inside diameter in a range of 32.5 to 34.0 mm, a total of ten vanes fitted to an inside circumferential surface of the anode body in a radial direction, and an inner strap and an outer strap provided to both of an upper surface and a lower surface of each vane, a distance of the inner strap and the outer strap being in a range of 0.8 to 1.2 mm, and each of the inner strap and outer strap being in contact with every second vanes for electrical connection of the vanes alternately. The anode body and the vanes are formed as one unit for simplification of a fabrication process.

Abstract: A cooling apparatus of a plasma lighting system. The system includes a power supply for supplying a power source; a magnetron for generating electromagnetic wave by the power source from the power supply; a bulb for generating light in accordance with that inert gas is ionized by the electromagnetic wave; and a case unit of a hermetic shape including the magnetron and the power supply therein for cooling heat generated from the magnetron. The plasma lighting system prevents heat of high temperature generated from the magnetron from being transmitted and foreign substance from being introduced.

Abstract: A noise filter for a high frequency generator maximizes a frequency band in which noise is attenuated by adjusting a spacing between winding turns of core inductors provided in the noise filter. The noise filter includes a coke coil having a first winding unit having a first spacing between turns thereof, a second winding unit having a second spacing between turns thereof and a third winding unit having a spacing the same as the first spacing between turns thereof. The first, second, and third winding units are connected in series to each other. The noise filter also includes a high-frequency energy absorbing member inserted into the choke coil. The high-frequency energy absorbing member is made of one of iron oxide, tin alloy and ferrite, and includes a sectional area to attenuate noise in a frequency band ranging from 30 MHZ to 1000 MHz.

Abstract: A magnetron for a microwave oven includes a yoke, an anode cylindrical body installed inside the yoke, a plurality of veins mounted inside the anode cylindrical body, a filament installed in a center of the veins, and an upper magnet and a lower magnet respectively mounted on an upper side and a lower side of the anode cylindrical body. The magnetron also includes an upper pole piece and a lower pole piece respectively installed between the anode cylindrical body and the upper and lower magnets. A length (L) from an external tip of a central part of the upper pole piece to an internal tip thereof, on which a hollow part is formed, is adjusted to suppress harmonics in the magnetron. Thus, generation of the harmonics may be effectively attenuated, and an output of a microwave may be enhanced by preventing power consumption of the magnetron which may be large due to interrupting harmonics.

Abstract: A magnetron includes an anode having an anode cylinder and anode vanes; a cathode having a filament; a condenser, a choke coil, and a plurality of leads for providing power to the filament; a plurality of magnets, pole pieces, and a yoke for forming a magnetic circuit; an antenna feeder and an antenna cap for transmitting a generated microwave outside of the magnetron; and a plurality of joints formed of a joining material between a metal component and a ceramic component of the magnetron. The joining material is diffused between the metal component and the ceramic component, to infiltrate into an inner part of the ceramic component directly, thereby joining the metal and ceramic components, and thereby also improving a reliability of a magnetron, facilitating a simple component assembly process and a simple magnetron fabrication process, permitting simplification of the fabrication process and reduction of a fabrication cost, and saving equipment cost as a high temperature furnace can be dispensed with.

Abstract: Disclosed is a cooling apparatus of a plasma lighting system comprising: a power supply for supplying a power source; a magnetron for generating electromagnetic wave by the power source from the power supply; a bulb for generating light in accordance with that inert gas is ionized by the electromagnetic wave; and a case unit of a hermetic shape including the magnetron and the power supply therein for cooling heat generated from the magnetron. The plasma lighting system prevents heat of high temperature generated from the magnetron from being transmitted and foreign substance from being introduced.

Abstract: A magnetron for a microwave oven includes a yoke, an anode cylindrical body installed inside the yoke, a plurality of veins mounted inside the anode cylindrical body, a filament installed in a center of the veins, and an upper magnet and a lower magnet respectively mounted on an upper side and a lower side of the anode cylindrical body. The magnetron also includes an upper pole piece and a lower pole piece respectively installed between the anode cylindrical body and the upper and lower magnets. A length (L) from an external tip of a central part of the upper pole piece to an internal tip thereof, on which a hollow part is formed, is adjusted to suppress harmonics in the magnetron. Thus, generation of the harmonics may be effectively attenuated, and an output of a microwave may be enhanced by preventing power consumption of the magnetron which may be large due to interrupting harmonics.

Abstract: Magnetron including a cylindrical anode having a resonant space formed therein and a cathode fitted therein, magnets fitted to upper and lower sides of the anode, a yoke fitted on outsides of the anode and the magnets to for a closed circuit, and cooling devices including a main cooling device to form a heat discharge path from the anode, and a supplementary cooling device to form a heat discharge path from the magnet direct or indirectly, wherein the main cooling device is an anode heat conductor having one end closely fitted to an outside surface of the anode, and the other end passed to the yoke and exposed to an external air, and the supplementary cooling device includes a magnet heat conductor closely fitted to an outside surface of the magnet, the magnet heat conductor having one side in contact with the outside case of the magnetron, or a yoke heat conductor closely fitted to an outside surface of a yoke plate, the yoke heat conductor having one side in contact with the outside case of the magnetron.

Abstract: A radio frequency magnetron device for generating radio frequency power includes a cathode at least partially formed from a diamond material. An anode is disposed concentrically around the cathode. An electron field is provided radially between the anode and the cathode. First and second oppositely charged pole pieces are operatively connected to the cathode for producing a magnetic field in a direction perpendicular to the electric field. A filament is provided within the electron tube which when heated produces primary electrons. Alternatively, a voltage is applied to the anode which causes primary electrons to emit from the diamond coated cathode. A portion of the primary electrons travel in a circular path and induce radio frequency power. Another portion of the primary electrons spiral back and collide with the cathode causing the emission of secondary electrons. The secondary electron emission sustains operation of the magnetron device once the device has been started.

Abstract: In a magnetron apparatus in accordance with the present invention, a first notch 17, a second notch 19 and a third notch 20 are formed in each of anode segments 15 disposed radially inside an anode cylinder 6, whereby the passage of high-frequency current flowing through the resonator comprising the two anode segments 15 adjacent to each other, the anode cylinder 6 and strap rings 9 and 10 is made narrow and long.

Abstract: A magnetron comprising an anode portion, a cathode portion provided in a center of the anode portion, a cylindrical interaction space formed of the anode portion and the cathode portion, and iron magnetic pole pieces located at both ends of the interaction space in an tube axis direction thereof. A relationship between a thickness Tg (mm) of a tapered portion of the magnetic pole pieces and a magnetic flux Bg (mT, at 25° C.) of a center of the interaction space is set to satisfy 155<Bg/Tg<165. It is possible to obtain a magnetron with substantially constant oscillating efficiencies, and it is accordingly possible to stabilize outputs of the microwave oven and to enable easy control of heating food.

Abstract: An optical magnetron is provided which includes a cylindrical cathode and an annular-shaped anode coaxially aligned with the cathode. The anode may include a plurality of wedges arranged side by side to form a hollow-shaped cylinder having the anode-cathode space located therein, and each of the wedges includes a recess which defines at least in part a resonant cavity having an opening exposed to the anode-cathode space. The anode alternatively may include a plurality of washer-shaped layers stacked atop each other. Each of the layers includes a plurality of recesses along an inner diameter which are aligned with recesses of the other layers to define a plurality of resonant cavities along an axis of the cylinder each having an opening to the anode-cathode space.

Abstract: A magnetron comprising an anode portion, a cathode portion provided in a center of the anode portion, a cylindrical interaction space formed of the anode portion and the cathode portion, and iron magnetic pole pieces located at both ends of the interaction space in an tube axis direction thereof. A relationship between a thickness Tg (mm) of a tapered portion of the magnetic pole pieces and a magnetic flux Bg (mT, at 25° C.) of a center of the interaction space is set to satisfy 155<Bg/Tg<165. It is possible to obtain a magnetron with substantially constant oscillating efficiencies, and it is accordingly possible to stabilize outputs of the microwave oven and to enable easy control of heating food.