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Publication numberUS2291948 A
Publication typeGrant
Publication date4 Aug 1942
Filing date27 Jun 1940
Priority date27 Jun 1940
Publication numberUS 2291948 A, US 2291948A, US-A-2291948, US2291948 A, US2291948A
InventorsBenedict Cassen
Original AssigneeWestinghouse Electric & Mfg Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
High voltage chi-ray tube shield
US 2291948 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

8- 1942- W B. CASSEN 2,291,948

HIGH VOLTAGE X-RAY TUBE SHIELD Filed June 27, 1940 ATTORNEY Patented Aug. 4, 1942 Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 27', 1940, Serial No. 342,745

4 Claims.

The present invention relates to X-ray tubes and particularly to such tubes operable at exceedingly high voltages;

High voltage X-ray tubes are being used more and more extensively by the medical profession for therapeutioal treatments. Although there appears to be two schools of thought as to the therapeutical value of high voltage X-nays for therapeutioal treatment, nevertheless one theory is that the higher the voltage; thegreater the therapeutical effect since the X-rays have a greater degree-of penetration.

To this-end the voltagesapplied to X-ray tubes now approximate one million volts and higher.

When tubes are operated at this voltage, they must be connected to a vacuum pump so that evacuation of the tube continues during operation, since occluded gases are liberated by the metallic parts of the tube under the stress of this exceedingly high voltage; Although con-- nected to a vacuum pump for the purpose of evacuating occluded gases, nevertheless the filamentary cathode has=heretoforebeen subjected to a certain amount of positive ion bombardment, which in many instances causes destruction of the cathode and, in any event, considerably shortens the life thereof.

It is accordingly anobject of the present invention to provide a cathode electrode for a high voltage X-ray tube'wherein such cathode is shielded from positive ionbombardment.

Another object of the present invention is the provision of a cathode electrode for a high voltage X-ray tube wherein the cathode is shielded from positive ion'bombard'ment and wherein the electrical fields generated within the tube cause the emission of electrons from the filament which bombard the anode to produce X-rays' of high penetrative power.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

Fig. 1 is an elevational view of an X-ray tube employing a cathode in accordance with the present invention.

Fig. 2 is a cross-sectional view on an enlarged scale of the X-ray tube as shown in Fig. 1 and showing more in detail the novel construction of the cathode electrode, and

Fig. 3 is a sectional view taken on the line Ill-III of Fig. 2.

Referring now to the drawing in detail, in Fig. 1 an X-ray tube 5 is shown which, for the sake of simplicity, is more or less of the conventional type; It should be understood, however, that X-ray tubes operable at voltages of one million volts or more naturally donot conform to the conventional type illustrated; but the spacing between'the electrodes is much greater and various other precautions must be taken in the way of insulation; etc., between parts of opposite instantaneous polarity. However, since the present invention is more concerned with the cathode construction, it is believed unnecessary that an X-ray tube as now known to" the art, operable at one million volts or more} be illustrated;

As in the usual construction, the-X-ray tube" comprises an enclosure or envelope 6' provided with an anode? having a target 8' of refractory metal, such as tungsten or the like, and disposed ladjacent thereto is a cathode" electrode I assembly As shown more in detail in Fig; 2,

the cathode assembly comprises aree'nt'rant portion in having a press l2 through which a pair of leading-in conductors l3 and I l are sealed which carry heating current for a circular filamentary cathode l5.

Secured to the reentrant stem illys u ch as by means of bands or clamps I6, is a metallic focusing cup ll witha flaredor mushroom head I8 having a large radii of curvature, adjacent the oppositely disposed anode. The focusing cup' is connected to-the filamentary cathodein any suit-- able manner,such for example as a conductor is, so that both are atthe same polarity dur-' ing operation and a diaphragm 26' is disposed in the cylindrioal'pa'rt ofthe focusing cupa short distancefrom the circular filamentary cathode.

This diaphragm is providedwith an aperture 22 having a diameter less than the inner diameter of the circular'filament'ary cathode, as can bemore'readily appreciatedfroni-Fig. 3; so that there is no straight line-flow of electrons from the oatho'de to theanode; and'by the same token, the diaphragm 2t prevents the flow of positive ions which would otherwise bombard the filamentary cathode.

Due to the position of the filamentary cathode just behind the edge of the aperture in the diaphragm, the lines of force generated by the electrical field pass through the aperture and bend around, ending on the filament IS. The electrons thus pulled from the filament are started with a backward component of velocity, but are slowed down in a short distance due to the field and are then accelerated in the forward direction at high velocity where they bombard the target 8, producing X-rays of great penetrative power.

Moreover, due to the depth of the diaphragm with its aperture 22 within the focusing cup 18 and the resulting electrostatic field, substantially all of the electrons after passing through the aperture, fiow in a straight line to the oppositely disposed anode. Consequently, these eaectrons do not impinge upon the walls of the envelope or housing, which would otherwise result in the building up of a high negative charge on the walls of the envelope. Moreover, any X-rays given off substantially normal to the surface of the target 8 have no harmful effect on the tube since they simply pass through the aperture 22, as shown by the arrow in Fig. 2, and are absorbed by the customary shields or the like.

During operation of the X-ray tube at the high voltage of one million or more volts, the envelope or housing 6 is connected to a suitable vacuum pump, as shown by the legend in Fig. 1. In addition, as is customary in tubes of such high voltage, the anode electrode may be cooled by the circulation of a cooling medium through an intake conduit 23 and a concentric outlet conduit 24. By the provision of such cooling means, the target 8 may be of lower melting point material than tungsten, if desired.

' It thus becomes obvious to those skilled in the art that an X-ray tube operable at voltages approximating one million volts is herein provided wherein a cathode electrode is employed Which is completely shielded from positive ion bombardment resulting from gases liberated from the metallic parts of the tube during its operation. Moreover, despite the complete shielding of the filamentary cathode, the electrical field is such that substantially all of the electrons are caused to flow from the thermionic cathode to the anode for the production of X-rays.

Although one specific embodiment of the present invention has been herein shown and described, it is to be understood that still further modifications may be made without departing from the spirit and scope of the appended claims.

- I- claim:

1. A high voltage X-ray tube comprising an enclosing envelope provided with a reentrant press, an anode in said envelope, a focusing cup provided with an end of large radii to prevent formation of intense electric fields and surrounding said reentrant press and supported thereby in longitudinal spaced relation to said anode, a filamentary cathode in the form of an annulus disposed within said focusing cup and longitudinally spaced relative to saidanode, and a shield positioned well within said focusing cup adjacent said cathode and electrically and mechanically connected to said focusing cup, and said shield having an aperture therein to prevent a straight line fiow of electrons from said cathode to said anode and the impingement of said cathode by positive ion bombardment during operation of said tube and to cause the flow of electrons only in an arcuate path through said aperture from said cathode to said anode.

2. A high voltage X-ray tube comprising an enclosing envelope, an anode in said envelope, a focusing cup spaced opposite said anode and of large radii of curvature to prevent formation of intense electric field, a filamentary cathode in the form of an annulus adapted to be heated to an electron emitting temperature and disposed within said focusing cup and longitudinally spaced relative to said anode, and a shield positioned adjacent said cathode and electrically and mechanically connected to said focusing cup, and said shield closing said focusing cup except for an aperture therein of less diameter than the diameter of said annular cathode to prevent the flow of electrons from said cathode to said anode except in an arcuate path through said aperture and to prevent positive ion bombardment of said cathode during operation of said tube.

3. A high voltage X-ray tube comprising an enclosing envelope, an anode in said envelope, a filamentary cathode in said envelope of annular form and disposed opposite said anode in longitudinal spaced relation thereto, a cylindrical focusing cup spaced longitudinally from said anode and surrounding said cathode and projecting in the direction of said anode well beyond the limits of said cathode to form a relatively deep recess for the latter, and a diaphragm disposed in said recess adjacent said cathode and electrically and mechanically connected to said focusing cu and said diaphragm forming a closure for said focusing cup except for an aperture therein to prevent a straight line flow of electrons from said annular cathode to said anode and the impingement of said cathode by positive ion bombardment during operation of said tube, and to allow the flow of electrons only .in an arcuate path through said aperture from said cathode to said anode.

4. A high voltage X-ray tube comprising an enclosing envelope, an anode in said envelope having a refractory metal target, an annular filamentary cathode in said envelope disposed opposite said anode in longitudinal spaced relation thereto, a cylindrical focusing cup spaced longitudinally from said anode and projecting in the direction of said anode Well beyond the limits of said cathode to form a relatively deep recess for the latter, and a diaphragm supported by said focusing cup adjacent said cathode and electrically connected thereto, and said diaphragm forming a closure for said cylindrical focusing cup and have an aperture therein of less diameter than that of said annular filamentary cathode to prevent the flow of electrons from said cathode to said anode except in an arcuate path through said aperture and to prevent positive ion bombardment of said cathode during operation of said tube.

BENEDICT CASSEN.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2651727 *7 Apr 19508 Sep 1953Eric Spear WalterX-ray tube
US2720607 *23 Jun 195211 Oct 1955Criscuolo Edward LSealed off, fine focus, long life, flash x-ray tube
US2961562 *5 May 195822 Nov 1960Gen ElectricOscillation suppression in high voltage electron guns
US3132198 *15 Jan 19625 May 1964Stauffer Chemical CoElectron beam furnace
US3649861 *9 Sep 197014 Mar 1972Picker CorpDouble focus x-ray tube
US4969173 *18 Dec 19876 Nov 1990U.S. Philips CorporationX-ray tube comprising an annular focus
US7382862 *28 Sep 20063 Jun 2008Moxtek, Inc.X-ray tube cathode with reduced unintended electrical field emission
US752934518 Jul 20075 May 2009Moxtek, Inc.Cathode header optic for x-ray tube
US7702077 *19 May 200820 Apr 2010General Electric CompanyApparatus for a compact HV insulator for x-ray and vacuum tube and method of assembling same
US77374241 Jun 200715 Jun 2010Moxtek, Inc.X-ray window with grid structure
US775625126 Sep 200813 Jul 2010Brigham Young Univers ityX-ray radiation window with carbon nanotube frame
US798339417 Dec 200919 Jul 2011Moxtek, Inc.Multiple wavelength X-ray source
US824797115 Aug 201121 Aug 2012Moxtek, Inc.Resistively heated small planar filament
US84983817 Oct 201030 Jul 2013Moxtek, Inc.Polymer layer on X-ray window
US852657424 Sep 20103 Sep 2013Moxtek, Inc.Capacitor AC power coupling across high DC voltage differential
US873613826 Sep 200827 May 2014Brigham Young UniversityCarbon nanotube MEMS assembly
US875045830 Nov 201110 Jun 2014Moxtek, Inc.Cold electron number amplifier
US876134429 Dec 201124 Jun 2014Moxtek, Inc.Small x-ray tube with electron beam control optics
US879261923 Mar 201229 Jul 2014Moxtek, Inc.X-ray tube with semiconductor coating
US880491030 Nov 201112 Aug 2014Moxtek, Inc.Reduced power consumption X-ray source
US881795011 Jun 201226 Aug 2014Moxtek, Inc.X-ray tube to power supply connector
US89295156 Dec 20116 Jan 2015Moxtek, Inc.Multiple-size support for X-ray window
US894834517 Jan 20133 Feb 2015Moxtek, Inc.X-ray tube high voltage sensing resistor
US89649435 Dec 201224 Feb 2015Moxtek, Inc.Polymer layer on X-ray window
US898935423 Apr 201224 Mar 2015Brigham Young UniversityCarbon composite support structure
US899562115 Jul 201131 Mar 2015Moxtek, Inc.Compact X-ray source
US907215426 Sep 201330 Jun 2015Moxtek, Inc.Grid voltage generation for x-ray tube
US90766287 Nov 20127 Jul 2015Brigham Young UniversityVariable radius taper x-ray window support structure
US91736239 Apr 20143 Nov 2015Samuel Soonho LeeX-ray tube and receiver inside mouth
US91744122 Nov 20123 Nov 2015Brigham Young UniversityHigh strength carbon fiber composite wafers for microfabrication
US917775524 Jan 20143 Nov 2015Moxtek, Inc.Multi-target X-ray tube with stationary electron beam position
US918402024 Jan 201410 Nov 2015Moxtek, Inc.Tiltable or deflectable anode x-ray tube
US93057351 Feb 20115 Apr 2016Brigham Young UniversityReinforced polymer x-ray window
US935138722 May 201524 May 2016Moxtek, Inc.Grid voltage generation for x-ray tube
US20070076849 *28 Sep 20065 Apr 2007Moxtek,IncX-ray tube cathode with reduced unintended electrical field emission
US20080296518 *1 Jun 20074 Dec 2008Degao XuX-Ray Window with Grid Structure
US20090022277 *18 Jul 200722 Jan 2009Moxtek, Inc.Cathode header optic for x-ray tube
US20090086923 *26 Sep 20082 Apr 2009Davis Robert CX-ray radiation window with carbon nanotube frame
US20090285360 *19 May 200819 Nov 2009Yang CaoApparatus for a compact hv insulator for x-ray and vacuum tube and method of assembling same
US20100243895 *14 Jun 201030 Sep 2010Moxtek, Inc.X-ray window with grid structure
US20130322602 *31 May 20125 Dec 2013General Electric CompanyInternal shielding x-ray tube
WO2007041498A2 *29 Sep 200612 Apr 2007Moxtek, Inc.X-ray tube cathode with reduced unintended electrical field emission
WO2007041498A3 *29 Sep 200619 Jul 2007Moxtek IncX-ray tube cathode with reduced unintended electrical field emission
Classifications
U.S. Classification378/138, 378/137, 313/344, 313/616, 313/7, 313/242
International ClassificationH01J35/00, H01J35/06
Cooperative ClassificationH01J35/06
European ClassificationH01J35/06