US2820165A

US2820165A - Means for cooling the windows of acceleration tubes for electrostatic generators

Info

Publication number: US2820165A
Application number: US379258A
Authority: US
Inventors: Denis M Robinson
Original assignee: High Voltage Engineering Corp
Current assignee: High Voltage Engineering Corp
Priority date: 1951-07-13
Filing date: 1953-09-09
Publication date: 1958-01-14
Anticipated expiration: 1975-01-14

Description

Jan. 14, 1958 D. M. ROBINSON 2,820,165

MEANS FOR COOLING THE wmnows OF ACCELERATION TUBES FOR ELECTROSTATIC GENERATORS Original Filed July 13, 1951 2 Sheets-Sheet 1 Jan. 14, 1958 D. M. ROBINSON- 2,820,165

MEANS FOR COOLING THE WINDOWS 0F ACCELERATION TUBES FOR ELECTROSTATIC GENERATORS Original Filed July 13, 195] 2 Sheets-Sheet 2 I N V EN TOR. lierzzis'JtCB03bas'an 2M BMW/m a) MEANS FOR COOLING THE WINDOWS F ACCEL-' ERATION TUBES; FOR' ELECTROSTATIC GEN? ERATORS Denis- M. Rohinson,,-Arlington, Mass.,-- assignor to High Voltage Engineering Corporation, Cambridge, Mass,

a corporation of Massachusetts Original application July-13, 1951, Serial No; 236,652,

now Patent No.-2,729','748,. datedJanuary 3, 1956. Divided ,and this application September 9, 1953, Serial No. 379,258

3 Claims. (Cl. 31335) This application. is a division of my co-pending applica' tion Serial No. 236,652; filed July 13, 1951, now.Patent No; 2,729,748, and is directed to subject matter required to .be divided out on March 31, 1952, because directed to an electric lamp discharge device with temperature mod ifying. means.

This invention relates to apparatus for sterilizingfoods,.

drugs and other materials or substances, or causing desirable chemical changes in material by ionizing radiations. More particularly it relates to the irradiation with.

resulting sterilization of such materials by the action of an electron beam of extremely high energy. ,It is shown in connection withmeansto effect irradiationin such manner as rapidly ;to scan such materials ,with'a high,

intensity beam so as to increase the instantaneous ionization density, and thereby reduce possible adverse effect on the taste, color, nutritive value, potency or other required properties of such materials.

The present invention utilizes and is applicable to any concentratedhigh-energy stream of electrons. Therefore,

while I have in the drawings illustrated though more or less diagrammatically certain forms of parts of theVan or magnetic field before the high intensity beam issues through the window of the acceleration tube, in which case the window is much elongated in the direction of travel of said .-high -intensity electron beam in its scanning action. Such-a window constitutes or is formed as a long narrow slot'covered by thin aluminum foil, and provision is made as herein disclosedfor carrying away the heat generated by thepassage of the electron beam through the window.

This is eifectedmore readily than if the same electron beam-were'continuously passing, with resultant intense.

heatingthrough the same small window area, instead of being moved back and forth along such narrow slot.

I herein .broadly claim the provision of means for cooling the elongated window.

I believe that an extremely intense ionization at a given point and at a giveninstant of time results in more efiective sterilization. The results of my invention-are accomplished by producing intense ionization ,by continuous electronbeams which are made possible as a result of the Vangde Graafi-High Voltage'Engineering Corporation n que I have stated that the objective. in the sterilizationof foodsand drugsis to inactive certain organisms without,

however, ,produci ng' undesirable. changes of taste or changes i nnut'ritive or medicinalqualities. This,.I have atent ascertained, is best achieved when the lowest possible ionic "eifects'result from the application of the-required sterilization dose.

Furthermore, my investigations show'that when sub in accordancewith my invention, many changes in taste or nutritive or medicinal qualities may be prevented: Not

only may changes in taste and potency actually be 're-' duced, but the irradiation dose requirements are at the Sametime actually reduced on some, at least, of the organisms presentin the material and substances subjected to the sterilization action of an electron beam of extreme intensity.

Hav-ingthus'set forth the objects of my invention and the general nature thereof, 1 will now disclose certain embodiments of means or apparatus by which 'I may practice my invention.

In the accompanying drawings:

Figi-l is adiagram, mainly in longitudinal section, illustrating the modification or change in position of the axis of an electron beam of extreme intensity after issuing as an approximately parallel beam from the lower end of the'acceleration tube of one form of a Van de Graaff electrostatic generator somewhat diagrammatically shown, such modification or change in position of the axis .of the beam occurring at extreme speed, as, for example, by oscillating such beam at a speed, of one thousand times a second or less, or more, by the actionof alternating current electromagnets, that is, with the scanning-occurring parallel to the plane of the said electromagnet coils,.the'

said electron beam being focused or given the desired convergence within the acceleration tube by a surrounding wise a widely flaring or flared lower end to providespace,

wherein the scanning action of a field occurs through the action of a pair of alternating current electromagnets, be

fore the electron beam issues through the window, which.

therefore is greatly elongated in the direction of the scanning movement of the electron beam,

Fig. 3 is a diagrammatic detail in side elevation and,

vertical section of the lower portion of an acceleration, tube of any desired type, but having a flaring or flared.

lower end terminating in an elongated narrow window and representing cooling means for such window;

Fig. 4 is a bottom plan view of the elongated narrow window represented in Fig. 2;

Fig. 5 is a diagrammatic view of the lower end of an acceleration tube of any type, provided with means to cool a window at or near the lower end thereof; and

Fig. 6 is a side elevation, but partly in vertical section,

of the lower end of the form of acceleration-tube shown in Fig. 1.

Referring more particularly to the drawings, and first to Fig. 1 thereof, a small portion, broken away, of one form or type of the acceleration tube of a Van de Graaff electrostatic generator, but to the use of whichv my invention is not limited, is indicated at 1. The said. generator is capable of producing a narrow beam of high: speed electrons, the energy whereof is or may beon theorder of several million volts and as much .as five million or more volts, and is manufactured by High Voltage Engineering Corporation.

The high speed electron beam emanatingfrom, the,

cathode of the acceleration tube .1 is indicatedat; 2. The

electrons of the. bea nZ are, accelerated throughthep,

vacuum region of the acceleration tube 1 in a manner not necessary to explain herein in detail, and in the construction shown in Fig. 1 they travel in a straight line or path and issue through the window 3 at the lower end thereof, having been focused by the focusing magnet indicated at 311 in Fig. 1.

Still referring to Fig. 1, at the proper distance below the window 3 of the acceleration tube 1 is provided a suitable support 4 which may be stationary or which, as is here the case, may be a conveyor such as a belt that is driven at a suitable speed forward, transversely to the direction of the axis of the electron beam 2. This motion is indicated as being to the left, as indicated by the arrow. While the said support 4 may be positioned at any suitable distance below the window 3 in the construction shown in Fig. l, I represent it as positioned at a distance of fifteen to forty centimeters therefrom, but as an electron beams scatters somewhat while passing through the air, I may reduce the length of the air path as much as possible, so that the material or product is almost in contact with the window 3.

I am aware that scattering always occurs in the window of an acceleration tube through which the electrons emerge. There is also scattering in any air path or gas path through which the electrons must pass on their way to the product on the conveyor belt or other support, and finally there will be very considerable scattering in the product itself. All of this is primarily elastic nuclear scattering.

The scattering in a gas is proportional to the square of the atomic number. Thus hydrogen or helium would scatter very much less than air and would be a preferred gas between the windows in Fig. 5, yet to be described.

The present invention and other related inventions assigned to High Voltage Engineering Corporation are based upon fundmental work done by the scientific group associated with the said High Voltage Engineering Corporation.

When the scanning action is above the window of the electron tube, as in Fig. 2 yet to be described, the product is below and close to the window, as will be more specifically referred to herein.

The product, material or substance to be sterilized is represented at 5, but because of space limitations is merely diagrammatically shown.

While not herein claimed, I provide means for scanning, moving to and fro, or sweeping the electron beam 2 at an extremely high speed, as for example, at a speed of 1,000 oscillations per second, and even more in certain cases. A high scanning frequency is necessary in order that uniformity of irradiation, particularly in the regions of the product near the surface, may be achieved. This scanning, moving to and fro, or sweeping of the electron beam may be in any suitable or satisfactory manner. In Fig. 1, I have indicated for the purpose the creation of a magnetic field directed at right angles to the direction of propagation of the electron beam 2. This will cause the deflection of the electron beam 2 in a direction at right angles both to the normal path of the electron beam 2 and to the direction of the magnetic field, with an amplitude of oscillation depending upon the energy of the electrons and the intensity of the magnetic field. It may be small or may be fifty degrees, sixty degrees or even ninety degrees.

In the construction shown in Fig. 1 there are provided two alternating-current magnetic coils or

magnets

6, 7. The axis ofthe alternating-current magnetic field is indicated by the line 8. The extent of spread, sweep or scanning movement of the electron beam 2 is indicated by two lines 9, 10. In Fig. l the angle of scan is represented as about fifty degrees. The electron beam 2 is scanned in a direction parallel to the plane of said magnetic coils '6, 7.

The magnetic field is created by an alternating current passing through the said

magnetic coils

6, 7. The electron beam will oscillate; that is, it will be given its scan ning movements about its normal beam position with a frequency which is that of the oscillating current, and with an amplitude of oscillation depending upon the strength of the magnetic field, which may be varied as desired. The location of the magnetic coils or

magnets

6, 7 is shown merely diagrammatically and in action they give the desired deflection of the electron beam 2. Any extent of angular displacement of the electron beam 2 in the vicinity of themagnetic field will cause a lateral movement of the center of the electron beam on the product 5, the magnitude of which depends, as stated, upon the strength of the magnetic field and also on the distance of the product 5 on the support 4 from the magnetic field. One or more magnetic coils may be used to accomplish the desired purpose.

In Fig. 2, and in side elevation in Fig. 6, is represented the lower end portion of a late type or model of acceleration tube of a Van de Graatf electrostatic generator and which acceleration tube may be otherwise similar to that shown in Fig. l, excepting that the lower end of said acceleration tube is shown as markedly outwardly flared or flaring at 21 to left and to right in said Fig. 2 that is, in two opposite directions so as in one direction to be in cross section of greatly elongated length as indicated, but the width of which flaring portion is about the same as the normal diameter of said acceleration tube above the flaring portion, or it may be less. The said flaring portion 21 terminates at its extreme lower end in a window 22, which is a long narrow slot and is covered by a thin aluminum foil 20. Such window must support atmospheric pressure on the outside with vacuum on the inside. The narrowness of the slot and the support given by the closely spaced long sides of the frame insure this.

The length of the said window 22 is preferably such that I may impart to the electron beam within said flaring portion 21 a scanning or sweeping motion extending through fifty degrees or more, and if desired as much as ninety degrees. For that purpose I employ

magnetic coils

23, 24, such as shown at 6, 7 in Fig. l, or I may employ suitably shaped electrodes, and I preferably make said magnetic coils or conducting plates small enough to position them suitably within the flaring portion 21. This gives close coupling with the electron beam and accordingly reduces the scanning power required. Also the material of the vacuum wall thus serves as a shield against stray external fields.

However, I may, as shown in Figs. 2 and 6, provide the magnetic deflection by placing

magnetic coils

23, 24, or parallel conducting plates, entirely outside the vacuum chamber of the acceleration tube.

Preferably the side walls constituting the flaring lower end of the acceleration tube are made of some nonmagnetic material for example, aluminum and the

magnetic coils

23, 24 are brought as close as possible to the two opposing faces of the flaring lower end 21 of the acceleration tube 1. In order to reduce eddy current loss in the side walls 26 of the said flaring lower end portion of the acceleration tube 1, the section or portion of the acceleration tube subject to the magnetic flux may be made of some plastic material so attached as to be vacuum-tight. So long as the electron beam is passing through the magnetic field, the deflection of the electron beam from its original direction continues to increase. After emerging from that field the electron beam continues in a straight path which is a prolongation of its path at the point of leaving the magnetic field. In order to obtain the desired efiect without large coils or iron cores, I prefer to have a relatively weak magnetic system and, therefore, I allow the electron beam a path-length within the magnetic field sufficient to produce the required deflection. With such arrangement it is perfectly possible to have an angle of scan of fifty degrees or even ninety degrees within the flaring end portion 21 of the acceleration tube 1.

In the just described construction or arrangement the conveyor belt, indicated at 25 and in said Figs. 2 and 6, is positioned close below the window 22 which is at the extreme lower edge of the said flaring portion 21.

By causing the scanning action to take place within the said flaring lower end portion 21 of the acceleration tube,

it is effected therefore before any scattering has taken place, and therefore the electron beam is thus acted upon while the electron optics are still rigid. It is pertinent here to point out that the electron optics of the Van de Graaff type of acceleration tube constant-potential accelerators are very favorable and indeed compare in kind with the precision of the electron microscope, with which, however, my invention has nothing to do.

As already set forth, the scanning action may be applied before the electron beam issues through the window 22 of the acceleration tube, as illustrated in Figs. 2, 4 and 6. In such case the window 22 must be long in the direction of the scanning movement of the electron beam, and it therefore is a long narrow slot covered by a thin aluminum foil. Such a window is advantageous also, as already indicated, in that it carries away the heat generated by the passage of the electron beam through it, more readily than if the electron beam were continuously passing through the same small area. The flow of a generated heat can be further increased by having the frame of the window 22 made of material of good heat conductivity, or it may be liquid cooled. The narrowness of the slot-like window 22 and the support given by the closely spaced long sides of the frame at the extreme lower flaring end 21 of the acceleration tube I assure that the window will support atmospheric pressure on the outside with a vacuum inside.

In addition, and whether the window has the shape of a long slot as set forth with respect to Figs. 2, 4 and 6, or whether it be substantially circular in cross section as may be the case in the construction shown in Fig. 1, I may, and desirably do, provide means other than the shape or structure of the window and its frame for cooling the window, as by scouring the atmospheric surface thereof with a blast of gas or with fine sprays of liquid or solid materials.

In Figs. 3 and 5 I have represented one means for the purpose, Fig. 5 showing such means applied to the lower end of an acceleration tube, the entire tube being of circular or substantially circular cross section, and Fig. 3 showing the same or similar means applied to the lower flaring end of the acceleration tube shaped as illustrated in Figs. 2 and 6.

In both Figs. 3 and 5 the lower end portion of an acceleration tube of a Van de Graafi or other type is diagrammatically indicated at 27.

Referring to Fig. 5, at a suitable distance above the extreme lower end of the acceleration tube 27 is provided an aluminum window 28 and at the extreme lower end of the said tube 27 is provided a very thin window 29, preferably thin aluminum foil, as for the previously described windows 3 and 22. The space between the two windows 28, 29 is filled preferably with helium as at atmospheric pressure. Supported suitably outside the acceleration tube 27 is a pump 31 connected at its intake side by a pipe 32 with the helium chamber 30 and at its output side also connected with the said helium chamber by a pipe 33 terminating in a jet-forming orifice 34, by which the helium gas is forcibly discharged by the pump 31 against the lower surface of the aluminum window 28. The gas can be cooled by suitable cooling coils or heat interchanger before being discharged against the window. The electron beam is shown diagrammatically by the arrow 35.

Having thus disclosed several illustrative embodiments of apparatus for practicing my invention, it is to be understood that although specific terms are employed, they are used in a generic and descriptive sense, and not for purposes of limitation, the scope of the invention being set forth in the following claims.

I claim:

1. A high-vacuum acceleration tube having means at one end portion for creating a beam of high-energy electrons for passage along said tube, a final electron-permeable exit window and another electron-permeable window spaced from and anterior to the said final electronpermeable exit window, the space between said windows being adapted to be filled with a gas, and a pump having an intake passage and a discharge passage, both said passages being in communication with the gas in said space, and said discharge passage terminating in a jetforming orifice positioned near the innermost window.

2. Apparatus in accordance with claim 1, wherein said gas comprises helium.

3. A high-vacuum acceleration tube having means at one end portion for creating a beam of high-energy electrons for passage along said tube, a final electron-permeable exit window and another electron-permeable window spaced from and anterior to the said final electron-permeable exit window, the space between said windows being adapted to be filled with a gas, and means in communication with the gas space to impart directed motion to the gas against that face of the said anterior Window that is in contact with the gas space.

References Cited in the file of this patent UNITED STATES PATENTS 2,053,002 Herrmann Sept. 1, 1936 2,093,288 Ogloblinsky Sept. 14, 1937 2,161,458 De Boer et a1. June 6, 1939 2,374,311 Schaefer Apr. 24, 1945 2,602,751 Robinson July 8, 1952 FOREIGN PATENTS 532,781 France Nov. 23, 1921 641,134 France Apr. 10, 1928 111,958 Austria Jan. 10, 1929