US2193602A - Device for accelerating electrons to very high velocities - Google Patents

Description

Marsh H2, 1940. PENNEY 2,193,62

DEVICE FOR ACCELERATING ELECTRONS TO VERY HIGH VELOCITIES Filed May 6, 1938 2 Sheets-Sheet 2 INVENTOR Gay/0rd M/ Pen/2% Patented Mar. 12, 1940.

STATES PATENT OFFICE DEVICE FOR ACCELERATING ELECTRONS TO VERY HIGH VELOCITIES Pennsyl Application May 6, 193a, Serial No. 206,379 6 Claims. (01. zen-27.5)

The invention relates to devices for accelerating electrons to very high velocities.

An object of the invention is to provide means for accelerating electrons to very high velocities prior to impinging them upon a target.

Other objects and advantages of my invention will be apparent from the following description and drawings, in which:

Figure 1 is a view, partly in elevation and partly in cross-section, of a device embodying my invention; I

Fig. 2 is a modification of Fig. 1;

Fig. 3 is a view in cross-section through the tube of Fig. 1;

Fig. 4 is a cross-sectional view similar to that of Fig. 3, with modifications therein;

Fig. 5 is a cross-section on lines V-V of Fig. 3;

Fig. 6 is a View, partly in elevation and partly in cross-section, of a detailed modification of Fig. 1; and

Fig. 7 is a diagrammatic view of a preferred circuit for applying energy to the device.

In my invention for accelerating electrons to a high velocity, I provide means for keeping the electrons from wandering to the walls of the discharge tube and also for accelerating the electrons to high velocity. I provide an annular vacuum accelerating chamber l9, which may have the square cross-section illustrated in Fig. 1, or the circular cross-section illustrated in Fig. 2. Other configurations may be utilized.

I provide a magnetic flux perpendicular to the plane of this annular chamber, which may be accomplished by having annular magnetic pole pieces H and i2 above and below the chamber, which pole pieces are connected to the core [3 of the electromagnet It. The magnetic field from this magnet acts to make the moving electron follow a circular path.

I also provide a second magnetic circuit to produce a flux through the central opening of this annular chamber, which may be provided by the electromagnet l5 having the poles l6 and I! extending into the annular opening. The magnetic fields from both of these electromagnets are changed in proportion to maintain the radius of the electron path substantially constant.

I also provide means to keep the particle focused. This can be provided, as illustrated more clearly in Fig. 5, by pole faces l8, i9, 26 and 25. These pole faces provide an electrostatic field which tends to repel the electrons from the walls. The pole faces 58 and 119 are preferably positive, and the pole faces 26 and 2t are preferably negative. The negative electrodes 28 and 2t repel the electrons, and the radial, centrifugal and electromagnetic forces keep the electrons from reaching the positive electrodes I 8 and i9.

If the electrons are accelerated by an increasing magnetic flux with both magnetic fields starting from zero at the same time, and the electron starts from rest, then the flux densities for a given radius or path in the two fields must bear a given ratio, and if these fluxes are maintained in this ratio while increasing, the radius will remain practically constant.

In Fig. 2, the air gap of the magnetic field of pole pieces It and [2 becomes smaller as the radius increases, so that the flux increases with the radius at the desired circle of rotation. This has the efiect of decreasing the radius whenever the electron arrives at a radius larger than the desired circle, and conversely increasing the radius whenever the electron gets inside of the desired circle. The flux density at the circle traveled by the electron is One-half'the average flux density over the area enclosed by said circle.

In Fig. 2, a stronger electrostatic field of the same frequency and phase as the magnetic field is applied to the electrodes I8, I5, 20' and H which have been shown as arcs of cylinders in place of the planes in Fig. 1. This stronger electrostatic field will correct any instability in regard to the plane of rotation.

If the electrons start from rest at the instant of zero flux, they are strictly in equilibrium at a given radius." However, I also provide means so that the electrons will have avelocity corresponding to that which they would have had it they had started from rest with the flux equal to zero. This velocity of the electrons is preferably accomplished by the means disclosed in Figs. 3

and 4. A hot cathode 25 is preferably utilized as a source of electrons, and this cathode is preferably in an arm 26 opening into the main part of the vacuum chamber Ill. The electrode 18 lining the wall is suitably broken for the entrance of this electron. Perforated discs 21 of any number are utilized for concentrating the electrons in the central portion of the arm 26. also located in the arm 26 to give the electron its acceleration by means of a surge applied thereto in order that the electron will reach the annular portion of the chamber it with the desired velocity.

Another arm 30 is also located in a tangential relationship with a portion of the accelerating chamber H3 and contains a target 3!, upon which the electron will impinge after it has reached Electrodes 28 are the desired high velocity. An electrode 32 is placed adjacent the opening of the arm into the annular chamber l0, andhas a suitable charge applied thereto at the proper moment to pull the electron or electrons from the annular orbit towards the target.

In Fig. 4, I have illustrated further modifications of the device. The electrostatic electrodes IS, IS, 20' and 2t are preferably spaced around the annulus in arc sections as illustrated by 2|. The other three electrodes have the relation to 25' as shown in Fig. 2. These sections are preferably symmetrically spaced and as shown, extend about 40 to 45 of annular length around the chamber. In the space intermediate the sections of the electrode, I preferably place small electrodes 4| in the form of rings to aid in keeping the electron, if necessary, in the center of the annular ring. These electrodes 4| are charged positively during the accelerating period with respect to the rest of the apparatus and act as a lens to correct any deviation from direction of the circular path about the desired center.

In order to get the electrons into the magnetic field at the proper time and with the desired direction, radius and velocity, I provide an electrode 43 at the juncture of arm 26 and the annular chamber. An electron shot into a uniform magnetic field, if it can go from no flux to uniform flux, will travel in a circle which is tangent to the original direction at the point where the electron enters the field. An impulse voltage is applied to the electrode 43 and the electrostatic field is sufilcient to counteract the magnetic field as the electron enters the annular chamber. This impulse positive voltage is applied at the instant just past the flux zero when the electron beam should have the proper velocity to travel in the circular path of the center of the annular chamber. The purpose of this electrostatic field is to counteract the magnetic field as the electrons enter, so that the electrons tend to travel about the axis of the annular chamber and not abouta center perpendicularto the motion at initial entrance to the flux. The electrode 43 is preferably at an angle as disclosed so that the effect is Weak when the electron is in the fringing flux and increases as the electron enters" the stranger field.

In order to remove the electrons from the circular orbit at maximum velocity and in the desired direction, I provide, in addition to the electrode 32, a coil 44 to which an impulse of current is applied at or near the maximum electron velocity. The coil consists of two parts in series one above and one below the vacuum chamber. At the instant of maximum electron velocity, an impulse current, preferably from a charged condenser and released by triggering grid-glow tube, is sent through coil 44 and in direction to oppose the main flux which first displaces the center and then deflects the electrons into tube 34' which contains target 35. Coil 44 should be adjustable in position and the optimum position determined experimentally. A mechanically moving laminated iron piece might be instead, or in addition, to be suddenly moved adjacent to the tube at a position adjacent electrode 32', so as to reduce the fiux density over a small region which first shifts the center of rotation and finally causes the electron to leave the annular chamher.

The arm 34" in Fig. 4 is also disclosed as substantially tangent to the adjacent curved end of the electrode 2| The target 35 is also disclosed as perpendicular to the path of the electron. If desired, perforated screens similar to 2'! may be placed so that only electrons substantially axially aligned with the target will impinge thereon.

I also contemplate utilizing one magnetic field instead of the two fields disclosed in Figs. 1 and 2. In this case, I provide the two pole faces 36 and 31 with projections 38 and 39 into the central opening of an annular chamber 40 set in with the fiat portion surrounding the projection 38 on pole piece 36, and the flat portion 46 surrounding the projection 39 on the pole piece 31, as illustrated in Fig. 6. This construction provides for the magnetic flux through the center and also through the annular chamber 40.

In Fig. 7, is a diagrammatic illustration of a preferred circuit for applying energy to the device. A sourceof alternating current 50 supplies a frequency preferably as high as possible that will not produce distortion. 500 to 1000 cycles are desirable for this source and a larger number may possibly be used. This frequency is applied to the single coll 5| that supplies the energy for the magnetic flux for the pole pieces 36 and 31 of Fig. 6, or it may supply both coils l4 and I5 of Figs. 1 and 2. The source 50 may be of any desired voltage. A branch 52 from this source preferably supplies the positive charge through a tapped transformer 53 to the interior electrodes l8 and I9 and the negative charge to the electrodes 20 and 2| as illustrated on the left-hand side of the view through the tube and pole pieces 36 and 31. The source 50 also preferably supplies the charge for the electrodes on the right-hand side from a branch 54 through a tapped transformer 55. The charge for the ring electrodes 4| may be similarly applied by a tapped transformer and have a return through electrodes 20, 2| to the transformer. Phase shifters 56 and 51 are preferably put in the branch circuits 52 and 54' and adjusted with tests by the well-known exploring coil and oscillograph so that the electrostatic field in the annular tube is in phase with and of the same frequency as the magnetic field.

The electricity and magnetic fields applied to the device may be of intensities depending, among other things, on the size and quality of the parts in a manner that will be apparent to those skilledin the art. Accordingly, the following values are to be taken in an illustrative and not in a limiting sense.

The ring electrodes 4| I prefer to have a length approximately 5% of the inner diameter of the annular chamber. The voltage applied to these ring electrodes and the plate electrodes is preferably such as to provide a potential gradient of 50,000 to 100,000 volts per centimeter adjacent the edges of the electrodes and an average potential gradient of 5000 to 20,000 volts per centimeter between these electrostatic electrodes. If the positive and negative electrodes l8, I9, 20 and 2| are approximately in the form of an inch square, there may be applied a difference of 20,000 volts between these positive and negative electrodes. Likewise, a potential difference of 30,000 to 40,000 volts may be applied between the ring electrode 4i and the negative electrode 20.

Iron for the magnetic circuit should be well laminated 'and of the best commercial grade. Near the pole faces especially great care should be taken to secure a uniform density of iron and a true surface of pole faces because uniformity of flux over the desired circle of rotation is very I important. circular.

As a specific example of dimensions in regard to Fig. 7. the annular chamber may be approximately one inch in overall diameter and the biased slopes of the adjacent pole pieces having as close to an average spacing of one inch or the diameter of the tube as possible. The slopes may be from 1 to 8". The spacing between the pole pieces axially of the ring is approximately of an inch. These inner pole faces may be approximately 3% inches in diameter and the overall diameter of the legs of the electromagnet may be from 6 to 6%; inches. Such values are, of course, illustrative and not limiting.

In the operation of the device, an electron is shot into the tube when the magnetic flux passes through zero and this electron is accelerated while the flux builds up to its maximum and, at this time, the electron is directed against the target. Electrons may also be shot into the tube and those arriving at the center line when the magnetic flux is zero accelerated and the the rest disregarded.

ll lhiie l have disclosed certain preferred embodiments of my invention, it is apparent that many modifications may be made in the form, arrangement and number ofelements disclosed therein. Accordingly, I desire only such limitations as are necessitated by the prior art.

I claim as my invention:

i. In combination with an annular evacuated chamber, means for projecting charged electrical particles tangentially into said annular chamber, means for accelerating said particles circumferentially of said chamber, and means for producing a magnetic field traversing said chamber substantially perpendicular to the principal plane thereof. the said magnetic field increasing in intensity as the outer periphery of the annulus is approached.

2. In combination with an annular evacuated chamber, means for projecting charged electrical particles tangentially into said annular chamber, means for accelerating said particles circumfer- The pole is, of course, preferably entially of said chamber, and means for producing an electric potential gradient sloping from points in said chamber which are laterally displaced from the principal plane thereof toward said principal plane, the polarity of said potential gradient being such as to accelerate said charged particles toward said principal plane.

3. In combination with an annular evacuated chamber, means for projecting charged electrical particles tangentially into said annular chamber,

means for accelerating said particles circumferentially of said chamber, means for producing an electric potential gradient sloping from points in said chamber which are laterally displaced from the principal plane thereof toward said principal plane, the polarity of said potential gradient being such as to accelerate said charged particles toward said principal plane, and means for producing a magnetic field travering. said chamber substantially perpendicular to the principal plane thereof, the said magnetic field increasing in intensity as the outer periphery of the annulus is approached.

4. In combination with an annular evacuated chamber, means for projecting charged electrical particles tangentially into said annunlar chamber, means for producing a varying magnetic field through the central aperture of the annulus, and means for producing a magnetic field normal to the principal plane of said annulus and traversing said chamber, said magnetic field increasing in intensity as the outer periphery of said annulus is approached.

5. In combination with an annular evacuated chamber, means for projecting charged electrical particles tangentially into said annular chamber, means for producing a varying magnetic field through the central aperture of the annulus,

means for producing a magnetic field normal tothe principal plane of said annulus and traversing said chamber, said magnetic field increasing in intensity as the outer periphery of said annulus is approached, a pair of conductors at points substantially displaced respectively on opposite sides of said principal plane, at least one annular conductor near the wall of said chamber in the region of said principal plane, and means for imparting to said pair of conductors an electrical potential relative to the last named conductor which is of the same polarity as said charged particles.

6. In combination with an annular evacuated chamber, means for projecting charged electrical particles tangentially into said annular chamber, means for producing a varying magnetic field through the central aperture of the annulus, means for producing a magnetic field normal to the principal plane of said annulus and traversing said chamber, said magnetic field increasing in intensity as the outer periphery of said annulus is approached, and means for-causing the second said magnetic field to vary in syncbronism with the first said magnetic field.

GAYLOR'D W. PM.

Images