US3066238A - Asynchronous beam scanning device - Google Patents

Asynchronous beam scanning device Download PDF

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Publication number
US3066238A
US3066238A US801320A US80132059A US3066238A US 3066238 A US3066238 A US 3066238A US 801320 A US801320 A US 801320A US 80132059 A US80132059 A US 80132059A US 3066238 A US3066238 A US 3066238A
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Prior art keywords
window
electron
current
scanning
pulses
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Expired - Lifetime
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US801320A
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English (en)
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Richard H Arndt
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General Electric Co
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General Electric Co
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Priority to NL249741D priority Critical patent/NL249741A/xx
Application filed by General Electric Co filed Critical General Electric Co
Priority to US801320A priority patent/US3066238A/en
Priority to GB9883/60A priority patent/GB901017A/en
Priority to DEG29282A priority patent/DE1121747B/de
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J33/00—Discharge tubes with provision for emergence of electrons or ions from the vessel; Lenard tubes

Definitions

  • Electron beam generators usually employ a long insulating evacuated tube for accelerating the electrons through a large potential difference existing between an electron gun including a hot cathode emitter at one end of the tube and an anode at the other.
  • the anode includes an electron permeable window through which the beam passes from the tube onto a substance being irradiated.
  • the beam is focused in the tube so as to create a beam diameter on the window in the range of 1 cm. in diameter which generally increases as it emerges to the atmosphere as the result of electron scattering in the window and from encountering atmospheric gas particles. lnevitably, the electron density is greatest near the beam center and appreciably attenuated near its margin.
  • a primary object of the present invention is to provide a charged particle beam generator that yields more useful radiation with a given power input.
  • Another object is to provide a beam generator scanning system that distributes the high and low intensity beam zones over the entire usable lengths of the beam transmitting window with the added effect of obtaining more uniform ionization in the substance being irradiated.
  • Still another object is to provide a beam generator with scanning means that enable simplifying the controls and eliminating the necessity for establishing careful phasing between the current pulses and the deflection flux.
  • the present invention involves apparatus and a system for obtaining uniform energy distribution over an electron permeable window and a product being irradiated, characterized by emission of electrons in symmetrical or unsymmetrical pulses to form a beam which is scanned both transversely of and along the window length over a predictable, but not successively repetitious pattern. This is achieved by a time varying scanning field rising and falling at a frequency that is predetermined and different than the pulse rate of the beam so that maximum beam energy will occur at different beam positions for each scan.
  • FIG. 1 is a schematic representation of a resonant transformer type of electron beam generator embodying the invention
  • FIG. 2 is a fragmentary section, taken on a line corresponding with 2-2 in H6. 1, showing part of the amide and electron exit window of an electron beam generator tube and products being irradiated;
  • FIG. 3 is a plan view of the electron exit window showing by a broken line how the beam changes position along the long dimension thereof;
  • FIG. 4 is similar to P16. 3 except that it shows by a broken line the beam path resulting from scanning across the narrow dimension of the window;
  • FIG. 5 is a diagram showing the relationhip of the accelerating voltage, the current pulses and the time vary-- ing flux that deflects the beam lengthwise of the window;
  • FIG. 6 is a plot of the beam travel along the lengthof the window during successive scans in accordance with the instant invention.
  • FIG. 7 shows the variations of the accelerating voltage and electron density with respect to the position of the electron beam on the window where ordinary linear sca'ndesigned to withstand voltages between its opposite ends in the range of 1 million volts and upward. It includes a plurality of glass rings 11 which are sealed in end-to-end relationship by intervening metal spacers 12 and it is enclosed at its upper end by a cathode mounting assembly including a focusing electron gun 13 having a hot cathode 14 and a control grid 15. Wires 16 pass through vacuumtight insulators 17 in order to carry heating current to the cathode 14.
  • Tube is terminated at its bottom end by a metal ring 18 to which is joined a round metal tube 19 and a flared tube section 20.
  • the flared tube 20 terminates in an adapter 21 that is closed by an electron permeable exit window 22 usually made of very thin titanium, aluminum or other metal of low atomic number.
  • the elements recited in this paragraph constitute the accelerating tube anode and as can be seen at 23 they are ordinarily grounded so as to be at zero potential level with respect to the cathode 14.
  • the electron beam represented by the dashed line 24, acquires suflicient energy to pass through the window 22 and irradiate a product 25 carried on a conveyor belt 26, for example, below the window.
  • the electron accelerating voltage is derived from the high voltage secondary winding of a resonant transformer 31.
  • the secondary 30 usually surrounds the accelerating tube 10. At its high potential upper end, winding 30 is connected to one cathode lead 16 and at its lower end 32 it is grounded at the potential level of the tube anode which is grounded at 23. Suitable taps 33 on the secondary winding are connected with corresponding intermediate electrodes 34 within the tube 10 so as to effect a gradual potential gradient between the ends thereof. More detail on the construction of the resonant transformer and an accelerating tube having the character of that here used as an example are obtainable from US. Patent No. 2,144,518.
  • the accelerating tube 10 and concentrically surrounding resonant transformer windings 30 may be enclosed in a metal tank 27, only a fragment of which is shown in FIG. 1, and which is filled with a dielectric medium such as oil or pressurized gas.
  • Means are provided for impressing a biasing potential between cathode 14 and a control grid 15 so that tube 10 will only conduct when the accelerating voltage wave is near its positive peaks.
  • Biasing energy is derived from the sinusoidal voltage which appears across the capacitance formed between tank 27 and a cap 37 located above tube 10.
  • the charging current associated with this capacitance voltage is fed into a bias control 40 through a wire 28 from cap 37 and a wire 29 from the high potential end of secondary winding 30.
  • bias control 40 is a rectifier and rectangular pulse forming circuit, not shown, whose output pulses are applied in phase with the accelerating voltage between cathode 14 and grid 15 through wires 38, 39 and the bias is adjusted so the tube will conduct in pulses that occur and persist only when the accelerating voltage is near the positive peaks of its sine wave curve.
  • the relation of the tube beam current pulses to the accelerating voltage, which appears between cathode 14 and window 22, may be seen in the upper portion of FIG. 5.
  • the accelerating voltage curve 44 may have an amplitude in the range of over 1 million volts and a frequency of 180 cycles per sec., in this instance. Since the tube 10 conducts only when the anode or window 22 is positive with respect to the cathode 14, current pulses 45 appear only during positive half cycles of the accelerating voltage. By proper adjustment of the bias circuitry, the current pulses may be biased to cut-off until voltage curve 44 reaches a value near its peak, at which time a substantially rectangular wave current pulse 45 is formed out of what would usually be a sinusoidal current wave form were it not biased.
  • the current pulse width may be taken as 72 on the 180 cycle per see. time scale for convenience, although a different conducting angle may be desirable in other cases.
  • a different conducting angle may be desirable in other cases.
  • the resonant transformer 31 includes a primary winding 46 of relatively few turns compared with the second ary, which primary is supplied with current through an amplitude control, symbolized by the device 47, which is in this case, supplied from a cycle per sec. generator 43.
  • Generator 48 includes the usual excitation controls (not shown) and is mechanically driven by a schematically represented synchronous motor 49.
  • Another alternating current generator 51 produces 1005 cycle per sec. current, in this instance, for supplying scanning coils 50 that deflect the beam 24 lengthwise of window 22.
  • Generator 51 is driven by motor 49 through a speed changer 52 so that the generated frequency shown in the lower curve 53 bears a predetermined relationship to the accelerating voltage and current pulses in FIG. 5.
  • the wave shape of generator 51 may be sinusoidal and used directly in that form or it may be modified by a wave shaping circuit, which is conventional and therefore only symbolized by the device 54 in FIG. 1.
  • a variable scanning voltage amplitude control inductor 55 In the same circuit there may also be included a variable scanning voltage amplitude control inductor 55. If wave shaping is adopted, the supply to coils 50 may be saw-toothed as suggested by curve 53 in the lower portion of FIG. 5.
  • the voltage from generator 51 is applied to means for scanning the electron beam 24 over the long dimension of the window 22 as suggested in FIG. 3 where the beam spot 56 is seen .0 execute that movement on the window.
  • the scanning means may be electrostatic but in this case they preferably take the form of electromagnet coils 50 located on opposite sides of anode tube 19.
  • Another set of scanning coils 59 are energized by a high frequency voltage which develops a flux that deflects the beam spot 56 extremely rapidly across the narrow dimension of the window 22 during each current pulse and whose component of motion is illustrated in FIG. 4.
  • Any suitable conventional oscillator (not shown) may be used to supply coils 59.
  • the cross scan frequency is in the range of 200 kilocycles per sec.
  • the cross scan frequency may be selected in view of the beam spot diameter, the window size and the desired amount of overlap of the beam spot. This will, in turn, usually be governed by the character of the product being irradiated, the rate at which it is conveyed, and its dosage requirements.
  • the electron beam 24 is deflected by using the entire flux wave developed by coils 50 rather than only the linear part as was done heretofore. This results in a beam current trace that is started and ended at a different position on the window for each successive tube current pulse. Moreover, the coinciding, most energetic, current and voltage peaks appear at different window positions so that window heat load is more uniformly distributed. To achieve this result it is necessary that the flrx which deflects the beam along the length of the window be such that it does not advance or retard the successive traces so much as to cause a repeating or coinciding trace in only a few cycles.
  • the lengthwise scanning flux voltage curve 53 is of such frequency that it passes through more than a whole cycle during a tube current pulse 45.
  • the beam moves over a period of time indicated by the dashed portion of the deflecting voltage curve 53.
  • the beam is moved from a point near the center of the window, to the far right end, back to center, to the far left end, and then back to beyond the center.
  • the peak current and accelerating voltage coincide near the window center as indicated by the proximity of dot 60 to the horizontal axis of no deflection.
  • deflcction begins at a diiferent point and proceeds in an op posite direction with the peak current and voltage occurring at the opposite side of the window center as indicated by the dot 60'.
  • the high frequency crosswise scan as suggested above, which gives the effect of converting the beam spot to a band whose width is that of the spot diameter and whose length is the width dimension of the window.
  • n 12 cycles
  • the resulting beam trace pattern along'"the window length is graphed with respect to time on the scanning frequency scale.
  • the points on each trace at which the pulse is started on the window are identified by dots, the peak voltage points by X, and the direction of beam movement by arrows.
  • the space between traces indicates the lapsed time between the end of one pulse and beginning of the next. It will be noted that the first and thirteenth traces are identical and that each successive starting point and peak occurs at a different window location.
  • preferred beam energy distribution may be obtained where the beam is scanned lengthwise of the window several times or during more than two complete scan cycles for each pulse. This is an important advantage of the novel unsynchronized scanning method disclosed herein, because it allows positioning the beam energy peaks so as to meet the dosage requirements of products having various irregular shapes and densities and whether or not they move at various speeds on a conveyor belt.
  • the time axis may be disregarded and all traces may be shifted to lie in a common plane vertical with the paper and extending along the long axis of Window 22
  • the beam spot is simultaneously and continually deflected crosswise of the window at a very high frequency so the-beam spot may be considered to take the form of a band that travels back and forth on window 22 in a direction and with a velocity indicated in FIG. 6.
  • deflecting voltage curve 44 may be saw-toothed, in which case the beam spot is deflected at a substantially linear velocity along the window 22. If absolute linearity is not required, which is often the case, a sinusoidal wave form of the same frequency from generator 51 may be applied directly to scanning coils 50 and the wave shaper 54 may be eliminated. Although, in this illustration, the relation of the scanning frequency to the pulse rate is maintained by driving both generators 51 and 48 from a common mechanically connected motor, it will be understood that a constant frequency scanning voltage may also be obtained from a crystal controlled oscillator, for example, which drives an electronic power amplifier, neither of which are shown. If this alternative is elected, only one generator such as 48 may be necessary since scanning power can be derived from it.
  • the invention is not limited to using any particular current pulse rate, accelerating voltage frequency or scanning frequency and the values used herein are to be considered illustrative only.
  • the exact parameters chosen in any case will depend upon the nature of the product being irradiated, the required depth dose, the conveyor speed and other variables that are taken into account by those skilled in the art of irradiation.
  • An important feature of the present invention resides in asynchronously relating the accelerating voltage and current pulses with the deflecting flux to the end that the maximum beam intensities will appear consecutively at different zones on the window and product.
  • Electron irradiation apparatus comprising an evacuated electron accelerating tube including an anode and an oblong electron permeable exit window at one end and an electron emitting cathode spaced therefrom, means for impressing a cyclically varying electron accelerating potential between said cathode and anode for projecting an electron current beam through the window, means for biasing said cathode so that beam current flows in pulses periodically with respect to the accelerating potential, means for deflecting said electron beam at a high rate across the narrow dimension of the window, coil means for creating a magnetic field that deflects the beam at a lower rate than said high rate along the greatest dimension of the window, means for energizing said coil means with current that varies at a frequency in cycles per second that is greater than the reciprocal of the pulse duration in seconds and which current has a different magnitude at the initiation of each beam current pulse in a predetermined number of such pulses, whereby the beam appears at different deflected positions on the Window when each successive pulse in a predetermined series
  • Electron irradiation apparatus comprising an evacuated tube including an electron emitting cathode, an anode and an oblong electron permeable exit window, a high voltage alternating current source connected between the cathode and anode for accelerating a beam of electrons to high energy and projecting it through the window, means for biasing said cathode to emit electrons in pulses periodically in a substantially constant phase relationship with respect to the accelerating voltage which varies in magnitude with time, a first means for deflecting said electron beam at a high rate across the narrow dimension, second means for creating an electron deflecting field for scanning the pulsed beam lengthwise of the window, means for energizing said deflecting means with an alternating voltage that is unsynchronized with the pulses and that passes through more than one cycle for each pulse duration, whereby the beam is deflected to a different window position at the beginning of each in a predetermined number of successive pulses and whereby the accelerating potential peaks occur at successively different window positions of the beam.
  • a method of imparting a substantially uniform integrated dose of high energy penetrating electrons across a substance and at any selected depth in the substance comprising the steps of developing in an evacuated chamber pulses forming an electron beam that emerges therefrom through an oblong electron permeable window, said electron pulses being generated at a constant frequency and constant phase angle with respect to an alternating field that accelerates them, projecting said electron pulses through an alternating flux that deflects them in a narrow band over the narrow dimension of the window, projecting said pulses through another alternating flux field that passes through fewer cycles in the same time than the first named flux, said other flux having a different magnitude for each of a number of consecutive pulses of electrons passing therethrough and the same magnitude after a predetermined number, whereby there is a coincidence between the same electron density of the pulses and the same accelerating field at consecutively different positions along the long dimension of the window and at the same position after said predetermined number.

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  • Particle Accelerators (AREA)
  • Electron Sources, Ion Sources (AREA)
US801320A 1959-03-23 1959-03-23 Asynchronous beam scanning device Expired - Lifetime US3066238A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
NL249741D NL249741A (nl) 1959-03-23
US801320A US3066238A (en) 1959-03-23 1959-03-23 Asynchronous beam scanning device
GB9883/60A GB901017A (en) 1959-03-23 1960-03-21 Improvements in asynchronous beam scanning device
DEG29282A DE1121747B (de) 1959-03-23 1960-03-22 Verfahren zur Herstelung einer gleichmaessigen Verteilugn der Energiedichte in einem pulsierenden Strahl geladener Teilchen

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US801320A US3066238A (en) 1959-03-23 1959-03-23 Asynchronous beam scanning device

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3176129A (en) * 1961-10-23 1965-03-30 Gen Electric Method and system for electron irradiation of materials
US3469139A (en) * 1968-02-27 1969-09-23 Ford Motor Co Apparatus for electron beam control
US3536951A (en) * 1966-11-04 1970-10-27 John De Sola Mosely Electron and heavy particle beam scanning systems
US3679930A (en) * 1969-08-13 1972-07-25 Ford Motor Co Method for increasing the output of an electron accelerator
DE2255273A1 (de) * 1971-11-15 1973-05-24 Ford Werke Ag Steuerjoch zum ablenken eines elektronenstrahls, insbesondere bei einem elektronenbeschleuniger
US4082958A (en) * 1975-11-28 1978-04-04 Simulation Physics, Inc. Apparatus involving pulsed electron beam processing of semiconductor devices
FR2476907A1 (fr) * 1980-02-26 1981-08-28 Razin Gennady Appareil de balayage par faisceau de particules chargees
US4396841A (en) * 1981-06-16 1983-08-02 Razin Gennady I Device for scanning a beam of charged particles
US5449916A (en) * 1994-09-09 1995-09-12 Atomic Energy Of Canada Limited Electron radiation dose tailoring by variable beam pulse generation

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3432293A (en) * 1966-01-06 1969-03-11 Glacier Metal Co Ltd Bearing materials and method of making same
GB8625912D0 (en) * 1986-10-29 1986-12-03 Electricity Council Thermochemical treatment

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE334193C (de) * 1921-03-11 Julius Edgar Lilienfeld Dr Verfahren zum Betriebe von Roentgenroehren mit periodischer Ablenkung des Kathodenstrahls
GB145084A (en) * 1918-04-09 1921-09-19 Julius Edgar Lilienfeld Process and apparatus for the production of rontgen rays
US2602751A (en) * 1950-08-17 1952-07-08 High Voltage Engineering Corp Method for sterilizing substances or materials such as food and drugs
US2730566A (en) * 1949-12-27 1956-01-10 Bartow Beacons Inc Method and apparatus for x-ray fluoroscopy
US2961561A (en) * 1957-10-29 1960-11-22 Gen Electric Internal magnetic deflection system for electron beam generator
US2977500A (en) * 1959-06-16 1961-03-28 Gen Electric Production and control of electron beams

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE334193C (de) * 1921-03-11 Julius Edgar Lilienfeld Dr Verfahren zum Betriebe von Roentgenroehren mit periodischer Ablenkung des Kathodenstrahls
GB145084A (en) * 1918-04-09 1921-09-19 Julius Edgar Lilienfeld Process and apparatus for the production of rontgen rays
US2730566A (en) * 1949-12-27 1956-01-10 Bartow Beacons Inc Method and apparatus for x-ray fluoroscopy
US2602751A (en) * 1950-08-17 1952-07-08 High Voltage Engineering Corp Method for sterilizing substances or materials such as food and drugs
US2961561A (en) * 1957-10-29 1960-11-22 Gen Electric Internal magnetic deflection system for electron beam generator
US2977500A (en) * 1959-06-16 1961-03-28 Gen Electric Production and control of electron beams

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3176129A (en) * 1961-10-23 1965-03-30 Gen Electric Method and system for electron irradiation of materials
US3536951A (en) * 1966-11-04 1970-10-27 John De Sola Mosely Electron and heavy particle beam scanning systems
US3469139A (en) * 1968-02-27 1969-09-23 Ford Motor Co Apparatus for electron beam control
US3679930A (en) * 1969-08-13 1972-07-25 Ford Motor Co Method for increasing the output of an electron accelerator
DE2255273A1 (de) * 1971-11-15 1973-05-24 Ford Werke Ag Steuerjoch zum ablenken eines elektronenstrahls, insbesondere bei einem elektronenbeschleuniger
US4082958A (en) * 1975-11-28 1978-04-04 Simulation Physics, Inc. Apparatus involving pulsed electron beam processing of semiconductor devices
FR2476907A1 (fr) * 1980-02-26 1981-08-28 Razin Gennady Appareil de balayage par faisceau de particules chargees
US4396841A (en) * 1981-06-16 1983-08-02 Razin Gennady I Device for scanning a beam of charged particles
US5449916A (en) * 1994-09-09 1995-09-12 Atomic Energy Of Canada Limited Electron radiation dose tailoring by variable beam pulse generation

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DE1121747B (de) 1962-01-11
NL249741A (nl)
GB901017A (en) 1962-07-11

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