US3204096A - Apparatus for projecting an electron beam along a curved path having variable impedance - Google Patents

Apparatus for projecting an electron beam along a curved path having variable impedance Download PDF

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Publication number
US3204096A
US3204096A US208504A US20850462A US3204096A US 3204096 A US3204096 A US 3204096A US 208504 A US208504 A US 208504A US 20850462 A US20850462 A US 20850462A US 3204096 A US3204096 A US 3204096A
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Prior art keywords
voltage
electron beam
cathode
electron
constant
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Expired - Lifetime
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US208504A
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English (en)
Inventor
Emmett R Anderson
Charles W Hanks
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Stauffer Chemical Co
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Stauffer Chemical Co
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Priority to BE634652D priority Critical patent/BE634652A/xx
Application filed by Stauffer Chemical Co filed Critical Stauffer Chemical Co
Priority to US208504A priority patent/US3204096A/en
Priority to GB27055/63A priority patent/GB987380A/en
Priority to FR940919A priority patent/FR1362376A/fr
Application granted granted Critical
Publication of US3204096A publication Critical patent/US3204096A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/24—Circuit arrangements not adapted to a particular application of the tube and not otherwise provided for
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
    • H01J37/305—Electron-beam or ion-beam tubes for localised treatment of objects for casting, melting, evaporating, or etching

Definitions

  • This invention relates to apparatus for projecting an electron beam along a curved path, and, more particularly, to means for controlling the curved trajectory of an electron beam in an electron beam furnace in order to guide it'to impinge upon and bombard a material to be heated.
  • a high-vacuum evacuation system is provided to remove such gases as rapidly as possible but, as in the case of entrapped gases which are released in bursts, the presence of a certain amount of gas and vapor ions, particularly in the melt zone, is unavoidable. If the gas ions invade the zone in which the electron guns are located a considerable amount of ditficulty may result, not the least of which is the creation of a short circuiting flow of electrons between gas ions in the discharge field between the cathode and anode of the electron gun. Consequently, it is preferred to space the electron guns some distance from the mold or melt zones and to employ a magnetic field for guiding and focusing the electron beams along curved paths to their remote targets.
  • power may be supplied to an electron-emissive cathode from a constant current source so that, when the cathode filament is heated to emit electrons at the desired rate and ideal conditions of equilibrium otherwise obtain, there is a constant discharge voltage of a desired value and, hence, a closely controlled acceleration and projection of the emitted electrons under steady-state equilibrium conditions.
  • a constant current source so that, when the cathode filament is heated to emit electrons at the desired rate and ideal conditions of equilibrium otherwise obtain, there is a constant discharge voltage of a desired value and, hence, a closely controlled acceleration and projection of the emitted electrons under steady-state equilibrium conditions.
  • the impedance variations cause corresponding variations in the discharge voltage, and, hence, variations in the velocities of the electrons accelerated by the electron gun.
  • an object of this invention to provide electric circuitry for maintaining a desired trajectory of a magnetically deflected electron beam in a furnace.
  • the electron beam furnace 1 which is shown in greatly simplified and partly schematicform, includes a furnace envelope 2 which is evacuated through ducts 4 by a conventional vacuum pump system or other vacuum source 6.
  • the electron beam target is shown merely as a molten pool 8 on top of material 9 contained within a mold or crucible 10.
  • the molten pool 8 is heated by bombardment of an electron beam 12 projected from an electron gun 14 under the influence and guidance of a magnetic field set up by an electromagnet 16.
  • the components of theelectron g ionically-emissive cathode 18, a focusing electrode 19, and an accelerating electrode or anode 20 which accelerates the electrons and projects them to a remote target, specifically, the molten pool 8.
  • a substantial current supplied by leads 22 from the secondary 23 of the filament transformer 24 is passed through the cathode filament 18 in order to heat it to suitable electron-emitting temperature.
  • the electron-accelerating anode 20 is connected by means of a conductor 25 to the furnace envelope, which is grounded as indicated at28.
  • a substantial negative voltage for example, in the order of 15 kv.
  • Magnet 16 has a U-shaped core, with a winding 30 on the center leg between the two parallel legs that form opposed pole faces on opposite sides of gun 14. One pole face is shown at 34, the other has been cut away in the section view. 'The coil 30 of the magnet 16 is energized by direct current through conductors 31 from a suitable rectifier 32 to generate a magnetic field with lines of force directed into the plane of the drawing toward the pole face 34, transverse to the electron beam, to
  • both the filament 18 and the magnet coil 30 through rectifier 32 are supplied with current, the magnitude of which is controlled by the output voltage of a constant current network, which varies as a direct function of the electron beam impedance.
  • the source of power for the system preferably is a three-phase, sixty-cycle commercial source 40 which is first supplied to a conventional, three-phase constantcurrent network 42.
  • Output leads 44, 45 and 46 of the constant-current network are connected to the primaryof a three-phase, step-up transformer 48, the secondary of which is connected to a suitable rectifier 50.
  • the positive output terminal of the rectifier 50 is connected to ground at 51 and the negative output voltage is supplied to a conductor 52.
  • a voltage of trajectory substantially 12 1S ependent upon both the velocity of the electrons in the ea an t e s reng of the mag 'c'field inii cing it, an varia' vo tage e- WWW-71 tween t e catho e an pro uce g corre- I spon ing variation in electron velocity, resulting in a 480 volts may be supplied at the source 40 and a negative direct current voltage of approximately 15 kv., at steadystate conditions, is supplied by conductor 52 to. the secthat any change in the output voltage of the constantcurrent network 42 will affect both the filament heating current and the current supplied to winding 30 which controls the strength of the magnetic field.
  • a sdbstantially constant three-phase, sixty-cycle current is delivered over leads 44, 45, and 46 to a step-up transformer, the output of which is delivered to a suitable rectifier 50.
  • a negative voltage in the order of i5 kv. is delivered by lead 52 to the secondary winding of the filament transformer 24.
  • the constant current source maintains the cathode l8 and the focusing electrode 19 connected thereto at a constant, high, negative potential, so that there is a constant voltage between the cathode and the electron-accelerating anode 20.
  • the cathode 18 is heated to emission temperature by means of the single-phase alternating current obtained from output conductors 44 and 45 of the constant-current network, and supplied to the cathode through variable transformer 56 and filament transformer 24.
  • the cathode heating current controls the cathode temperature, which in turn determines the voltage needed to draw from the cathode sufficicnt emission current to match the current supplied to the electron beam by the constant current supply.
  • Variable transformer 56 is adjusted to give the desired value of beam voltage under steady-state equilibrium conditions.
  • the step-up transformer 48 and rectifier 50 couple the output of constant current network 42 in series with the electron beam 12.
  • the series circuit path extends from the negative terminal of the rectifier through conductor 52 and the secondary winding of transformer 24 to the filament 18 of the electron gun 14.
  • the path extends through the electron beam 12 to the top of the material 9 in crucible 10, and then through the material, crucible, and furnace envelope 2 to the positive terminal of the rectifier 50 via the ground return existing between points 28 and 51. Since the output of the rectifier 50 is the stepped up rectified output of the constant current network 42, the current in the series circuit including the electron beam is constant. From Ohms Law, the beam voltage must vary with the impedance of the beam path inasmuch as the beam current is maintained constant. Consequently, as the impedance fluctuates irregularly, so does the beam voltage.
  • the impedance is decreased if the filament 18 becomes overheated, for example by ion bombardment, causing it to emit an excessive amount of electrons, and this too leads to a loss of beam power and unsatisfactory operation. Either event may lead to breakdown and arcing, loss of power in the beam, and damage to the furnace.
  • the impedance of the beam path is a portion of the output load of the rectifier 50 by virtue of the above-noted series circuit connection therebetween, Likewise, the beam path impedance is a portion of the load presented to the output of the constant current network 42 inasmuch as such output is coupled through the transformer 48 and rectifier 50 to the series circuit which includes the electron beam.
  • variation in the impedance of the beam path constitutes variation in the load of the constant current network 42. Since the constant current network maintains the load currcnt'at a constant level, the output voltage of the constant current network at leads 44, 45, and 46 necessarily varies in accordance with the impedance of the load, and therefore with the impedance of the beam path.
  • the beam voltage varies directly with the beam path impedance and, thus, it can be said that the output voltage of the constant current network correspondingly varies in accordance with the beam voltage, viz., beam voltage variations are reflected in like variations in the output voltage of the constant current' network.
  • the impedance of the beam path drops, there is an almost immediate drop, within about one cycle, in the voltage supplied through leads 54 and 55 and transformers 56 and 24 to filament 18.
  • the filament current is reduced and the cathode begins to cool. Since a small drop in cathode temperature greatly reduces the thermionic emission of electrons from the cathode, this arrangement provides a fast and powerful voltage restoring means for holding the beam voltage close to a desired average value.
  • the reduced output voltage of the constant current network is applied to such transformer.
  • This effects a decrease in the output voltage of the transformer as applied to the rectifier 32, and therefore in the D.C. output voltage of the rectifier which energizes the coil 30 of electromagnet 16.
  • the flow of current through the coil ishence decreased, resulting in a decrease in the strength of the magnetic focusing field generated by the electromagnet.
  • a rise in beam voltage effects a rise in the constant current network output voltage at leads 44 and 45.
  • This rise in constant current network output voltage is applied to the transformer 58, to in turn increase the output voltage applied therefrom to the rectifier 32.
  • the rectifier voltage is thus increased as is therefore the current through the coil 30.
  • Apparatus for projecting an electron beam to a target along a curved path having variable impedance comprising:
  • (d) means energizing said electromagnet with said source voltage to vary magnetic field strength in opposition to variations in beam voltage for maintaining the path of the beam substantially constant.
  • Apparatus for projecting an electron beam along a curved path having variable impedance comprising:
  • An electron beam furnace comprising:
  • an electromagnet having opposed pole faces disposed upon opposite sides of the electron beam to provide a transverse magnetic field for deflecting the beam along a curved path leading to the target;
  • a filament transformer connected to said first variable transformer and connected to supply heating current to said filamentary cathode, whereby the filament heating current varies as the beam voltage varies;
  • (k) a rectifier connected to said second variable transformer and connected to supply direct current to said electromagnet, whereby the strentgh of the magnetic field varies as the beam voltage varies.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Electron Sources, Ion Sources (AREA)
US208504A 1962-07-09 1962-07-09 Apparatus for projecting an electron beam along a curved path having variable impedance Expired - Lifetime US3204096A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE634652D BE634652A (ko) 1962-07-09
US208504A US3204096A (en) 1962-07-09 1962-07-09 Apparatus for projecting an electron beam along a curved path having variable impedance
GB27055/63A GB987380A (en) 1962-07-09 1963-07-09 Improvements in or relating to electron beam furnaces
FR940919A FR1362376A (fr) 1962-07-09 1963-07-09 Appareil destiné à projeter un faisceau électronique le long d'un trajet curviligne ayant une impédance variable

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US208504A US3204096A (en) 1962-07-09 1962-07-09 Apparatus for projecting an electron beam along a curved path having variable impedance

Publications (1)

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US3204096A true US3204096A (en) 1965-08-31

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US (1) US3204096A (ko)
BE (1) BE634652A (ko)
FR (1) FR1362376A (ko)
GB (1) GB987380A (ko)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3420977A (en) * 1965-06-18 1969-01-07 Air Reduction Electron beam apparatus
DE4391006C2 (de) * 1992-03-11 2002-10-17 Charles W Hanks Elektronenstrahlkanone
US6476340B1 (en) 1999-04-14 2002-11-05 The Boc Group, Inc. Electron beam gun with grounded shield to prevent arc-down and gas bleed to protect the filament

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3068309A (en) * 1960-06-22 1962-12-11 Stauffer Chemical Co Electron beam furnace with multiple field guidance of electrons
US3087211A (en) * 1960-05-27 1963-04-30 Stauffer Chemical Co Electron-beam furnace with opposedfield magnetic beam guidance

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3087211A (en) * 1960-05-27 1963-04-30 Stauffer Chemical Co Electron-beam furnace with opposedfield magnetic beam guidance
US3068309A (en) * 1960-06-22 1962-12-11 Stauffer Chemical Co Electron beam furnace with multiple field guidance of electrons

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3420977A (en) * 1965-06-18 1969-01-07 Air Reduction Electron beam apparatus
DE4391006C2 (de) * 1992-03-11 2002-10-17 Charles W Hanks Elektronenstrahlkanone
US6476340B1 (en) 1999-04-14 2002-11-05 The Boc Group, Inc. Electron beam gun with grounded shield to prevent arc-down and gas bleed to protect the filament

Also Published As

Publication number Publication date
GB987380A (en) 1965-03-31
BE634652A (ko)
FR1362376A (fr) 1964-05-29

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