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US3783288A
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Pulsed vacuum arc operation of field emission x-ray tube without anode melting
Assignee: Field Emission Corp
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Filing: 1972-06-26
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Granted: 1974-01-01
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Expires: 1992-06-26
Abstract
Abstract A field emission x-ray apparatus and pulsed vacuum arc method of operation is described in which a plurality of extremely high voltage pulses of short duration and high repetition rate are applied between the anode and cathode of the x-ray tube to provide an electron discharge of low energy density below about 20 joules per square centimeter to prevent anode melting, which greatly increases the useful lifetime of such tube. For example, with a tube having a conical anode of tungsten having a surface area of 1.8 square centimeter, pulses of 350 kilovolts and 1,000 amperes with a width of 30 nanoseconds, a repetition rate of 1,000 pulses per second can be employed with an energy of 10.5 joules per pulse to provide the tube with a useful life in excess of 200,000 pulses. This increased tube life results from recognition and exploitation of the fact that, at higher pulse voltages, the anode temperature rise per pulse is reduced due to the fact that the electrons penetrate through a thicker surface layer of the anode. The high voltage, greater than about 250 kilovolts, of the pulses also give improved results in radiographic apparatus, such as is employed for x-raying the human chest, since the resulting film radiographs are of better contrast and contain more useful diagnostic information.
Inventors
- 👤 J Barbour
- 👤 F Charbonnier
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 08:50
CPC Classifications
H; H05; H05G; H05G1/00; H05G1/08; H05G1/60; H01; H01J; H01J35/00; H01J35/22; H05G1/10; H05G1/20
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
218 words
Pulsed x-ray apparatus comprising: an x-ray tube including an evacuated envelope containing field emission cathode means and an anode which emits x-rays; a high voltage pulse generator having its output connected to said x-ray tube; exposure control means for triggering said pulse generator and causing it to apply a pulse train containing a plurality of electrical pulses between said cathode and said anode to produce a corresponding number of x-ray pulses during one exposure time period whose duration is determined by said control means, said electrical pulses causing the field emission of electrons from said cathode and the formation of a vacuum arc of vaporized cathode materIal so that for each electrical pulse said anode is bombarded with an electron discharge of extremely high voltage and high current and emits a corresponding x-ray pulse; and said electrical pulses having a peak voltage of at least 250 kilovolts and a narrow width so that the anode is bombarded with electron discharge pulses each having an energy density below that causing anode melting and the total number of pulses per exposure and the pulse repetition rate of said pulse train is such as to prevent the anode from being heated to a final maximum temperature above the melting point of the anode material at the end of said exposure period.
Claim 2
Dependent Claim
218 words
Pulsed x-ray apparatus comprising: an x-ray tube including an evacuated envelope containing field emission cathode means and an anode which emits x-rays; a high voltage pulse generator having its output connected to said x-ray tube; exposure control means for triggering said pulse generator and causing it to apply a pulse train containing a plurality of electrical pulses between said cathode and said anode to produce a corresponding number of x-ray pulses during one exposure time period whose duration is determined by said control means, said electrical pulses causing the field emission of electrons from said cathode and the formation of a vacuum arc of vaporized cathode materIal so that for each electrical pulse said anode is bombarded with an electron discharge of extremely high voltage and high current and emits a corresponding x-ray pulse; and said electrical pulses having a peak voltage of at least 250 kilovolts and a narrow width so that the anode is bombarded with electron discharge pulses each having an energy density below that causing anode melting and the total number of pulses per exposure and the pulse repetition rate of said pulse train is such as to prevent the anode from being heated to a final maximum temperature above the melting point of the anode material at the end of said exposure period.
Claim 3
Dependent Claim
15 words
An x-ray apparatus in accordance with claim 1 in which the anode material contains tungsten.
Claim 4
Dependent Claim
40 words
An x-ray apparatus in accordance with claim 1 in which the electrical pulses have a peak voltage between 250 and 600 kilovolts and the electron discharge pulses bombarding the anode have an energy density below 20 joules per square centimeter.
Claim 5
Dependent Claim
22 words
An x-ray apparatus in accordance with claim 3 in which the energy density is between 5 and 15 joules per square centimeter.
Claim 6
Dependent Claim
24 words
An x-ray apparatus in accordance with claim 1 in which the field emission cathode means includes a plurality of separate spaced sharp emitting elements.
Claim 7
Dependent Claim
15 words
An x-ray apparatus in accordance with claim 5 in which the emitting elements are needles.
Claim 8
Dependent Claim
23 words
An x-ray apparatus in accordance with claim 5 in which the emitting elements are rings having sharpened inner edges surrounding a conical anode.
Claim 9
Dependent Claim
29 words
An x-ray apparatus in accordance with claim 1 in which the pulse rate is at least 500 pulses per second and the pulse width is less than 200 nanoseconds.
Claim 10
Dependent Claim
61 words
An x-ray apparatus in accordance with claim 1 in which the anode is made of tungsten, the peak voltage is between 300 and 450 kilovolts, the peak current is 1,000 amperes or more, the energy density of the electron discharge pulses bombarding the anode is 15 joules per square centimeter or less, and the pulse width is 50 nanoseconds or less.
Claim 11
Dependent Claim
181 words
A pulsed radiograph method comprising: producing a pulse train containing a predetermined number of electrical pulses during one x-ray exposure time period, said pulses being of high current of at least 500 amperes and high voltage of at least 250 kilovolts peak voltage; applying said electrical pulses between a field emission cathode means and an anode of tungsten in an x-ray tube, to cause a plurality of x-ray pulses to be emitted from said anode by a field emission vacuum arc electron discharge operation during said exposure time period; transmitting said x-ray pulses through an object to form a plurality of x-ray images of said object; exposing a radiographic film with multiple images corresponding to the x-ray images of said object within said exposure time period; and controlling the number of pulses in said pulse train, the pulse repetition rate and pulse width so that the anode is bombarded with electron discharge pulses having an energy density less than 20 joules per square centimeter for each pulse and the tungsten anode is heated to a maximum temperature below its melting point.
Claim 12
Dependent Claim
181 words
A pulsed radiograph method comprising: producing a pulse train containing a predetermined number of electrical pulses during one x-ray exposure time period, said pulses being of high current of at least 500 amperes and high voltage of at least 250 kilovolts peak voltage; applying said electrical pulses between a field emission cathode means and an anode of tungsten in an x-ray tube, to cause a plurality of x-ray pulses to be emitted from said anode by a field emission vacuum arc electron discharge operation during said exposure time period; transmitting said x-ray pulses through an object to form a plurality of x-ray images of said object; exposing a radiographic film with multiple images corresponding to the x-ray images of said object within said exposure time period; and controlling the number of pulses in said pulse train, the pulse repetition rate and pulse width so that the anode is bombarded with electron discharge pulses having an energy density less than 20 joules per square centimeter for each pulse and the tungsten anode is heated to a maximum temperature below its melting point.
Claim 13
Dependent Claim
39 words
A radiography method in accordance with claim 10 in which said object is an adult human chest, the peak voltage is between 300 and 450 kilovolts and the energy density is between 5 and 15 joules per square centimeter.
Claim 14
Dependent Claim
40 words
A radiography method in accordance with claim 10 in which the x-ray exposure is formed by at least 10 pulses having a pulse width of less than 100 nanoseconds and a repetition rate of at least 500 pulses per second.
References Cited (Backward Citations)
US3309523A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-12-31 | 1977-07-02 | 1978-01-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-12-31 | 1981-07-02 | 1982-01-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-12-31 | 1985-07-02 | 1986-01-01 | $7700.00 | Window Closed / Lapsed |