US2394073A - Electron accelerator - Google Patents

Description

Feb. 5, 1946.

W. F. WESTENDORP ELECTRON ACCELERATOR Filed Sept. 10, 1943 Fig. I.

Inventor: Willem F. Westendorp,

His

ttorney.

Patented Feb. 5,

rmc'rnou ACCELERATOR Willem F. Westendorp, Schenectady, N. Y., as-

slgnorto General Electric Company. a corporation of New York Application September 10, 1943, Serial No. 501,155

(on. sis-44) 4 Claims.

The present invention relates to apparatus for accelerating charged particles, such as electrons, by means of magnetic induction effects. I

Apparatus of the character referred to typically includes a closed vessel and a magnetic system for producing a time-varying magnetic field of such space distribution as to confine electrons projected within the vessel to a circular orbit along which the electrons are continuously accelerated as the magnetic flux through the orbit increases ,in magnitude. When the electrons have been accelerated to a high velocity, they may be diverted from the accelerating orbit and used for the generation of X-rays or for the production of other useful eflects.

Some of the difliculties encountered in the operationof an electron accelerator are due to the accumulation of electric charges upon theinterior walls of the evacuated enclosure in which the acceleration of the electrons occurs. Such charges may be conducted away by a conducting coating applied to the inner surface of the evacuated enclosure. It is difllcult, however, especially in a high-powered apparatus, to provide a coating having sumciently high electric resistivity to prevent the generation of excessive 0 circulatory current therein.

In accordance with my present invention this dificulty has been overcome by subdividing the conductive coating intoa number of sections connected by external jumpers of high electric resistance. Circulatory currents then no longer are produced by the main magnetic flux. Such currents as are induced are produced by, the

much weaker flux traversing the boundaries of any one section.

The features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a partially sectionalized view of an induction accelerator embodying my inventionyFig. 2 is a plan view partly in section of an annular electron chamber showing the high resistance connections between sectors of the chamber, and Fig. 3 is a fragmental view of electrode structure.

Referring particularly to Fig. 1, there is shown in section a tubular glass vessel it closed on itself to provide a circular orbit in which electrons may be accelerated to a high voltage. The" vessel I0 is hermetically sealed and preferably highly to a vacuum pump (not shown).

The accelerating mechanism comprises a magnetic structure having rotationally symmetrical (i.e. circular) pole tapered pieces ll, l2 which are coaxial with the annular vessel It. These pole pieces are constituted of laminated iron held in assembly (by means not shown), the oppositely facing central portions being of essentially planar character. For decreasing the reluctance of the path between the opposed pole faces, there is provided an insert in the form of two laminated iron disks l3, id. An externally closed magnetic circuit between the base portions of the pole pieces is provided by iron cores I 5, IS, IT and i8.

The magnetic structure is excited by means of a pair of series-connected coils l9 and 20 which surround the pole pieces I I and i2 and which are energized in such manner as to produce a timevarying flux in the magnetic circuit.

' The coils i9 and 2b are connected in series with one another and across a condenser (not shown) having such capacity as to resonate with the inductance of the coils at a frequency corresponding to the desired frequency of operation of the apparatus. To supply the losses of the resonant circuit thus formed the coils i9 and 20 may be coupled to primary windings 22 and 22' which are connected in series and energized from an A.-C. power source, the connections not details of construction and mode of operation of an electron accelerator of this type now are well understood and are described in various prior publications.

Within the closed vessel ill (Fig. l) and also within the region of influence of the magnetic field produced bythe pole pieces ll, l2 there is provided a thermionic cathode 24 (Fig. 3) which, in connection with a cooperating anode 25 serves to generate an intermittent stream of electrons.

Leading-in conductors 26 and 21 are indicated.

The electrode structure and other details of a typical electron 'accelerator are described in an article entitled A 20-Million Electron-Volt Betatron or Induction Accelerator by 0. W. Kerst.

in Review of Scientific Instruments, 'vol. 13

(1942), pages 307 to 394, and hence need not be 4 here described in detail.

My present invention is concerned with the accelerator chamber. As shown in Fig. 2 the accelerator chamber may be made up of a plurality tenor coating is subdivided into zones.

of subdivisions as indicated. These are cemented to one another in gas-tight relation. The electrodes are introduced through a side tube 28. The exhaust of the gas content occurs through a second side tube 29.

The interior wall of the annular: chamber is provided with coatings 30 of silver or other suitable metal, as indicated by the stippling. The coatings are subdivided and the respective subdia visions are insulated from one another by disfrom the conductive coatings of each section as 1 indicated at 33. Between the respective conductors 32 are connected resistances 36 of high value, for example of the order of 1000 ohms each. Cir culatory currents through the respective coatings would encounter the sum of these resistances and hence could be only of negligible value.

What I claim as new and desire to secure by Letters Patentof the United 'States, is:

1. An electron discharge device comprising-an annular receptacle of non-conductive material providing a chamber for'thepassage of electrons therein, a plurality of electrically distinct zones of conductive material on the interior 'wall of aid chamber, and conductors having a materially higher resistivity than said zones respectively connecting said respective zones electrically to adjoining zones, thereby producing a highre sistance conductor which is substantially coextensive with said annular receptacle.

2. An electron discharge device comprising an annular receptacle providing a discharge space for electrons, a plurality of zones of conductive material on the interior surface thereof, electrically insulated from one another, external electrical conductors for each of said zones, and re: sistors connected between said cxtcrnalconductors to provide a continuous circuit through said conductive coating.

3. An electron discharge device comprising a channel-shaped envelope consisting of a plurality of members of glass cemented to one another in vacuum-tight relation, separate films oivmetal on the respective interior surfaces of said members, electrical conductors extending from each of said films to'the exterior, and electrical resistances connected between said conductors, said resistances having a value of the order 01 1000 ohms. v,

4. An electron discharge device comprising the combination of an electromagnetic structure for producing a time-varying magnetic flux, a re= ceptacle linked with said flux, consisting of nonconductive material and providing a chamber for the acceleration therein of electrons, a chargedissipating coating on the interior wall of said receptacle, said coating being divided into a plurality of distinct segments, high resistance conductors connecting said segments, thevresistivity of said segments and connecting conductors collectively being so high that only negligible rent is induced therein by said flux.

WIILEM- F. WESTENDORP.

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