US2306860A - Electron discharge device for very high frequencies - Google Patents

Description

Dec. 29, 1942. n Q H, BLACK 2,306,860

ELECTRON DISCHARGE DHVIICE FOR VERY HIGH FREQUENGIES Filed Aug. 29, 1940 l lll/l l/ /nyenor f I Atta/'ne Patented Dee. 29,'V 1942 ELECTRON DISCHARGE DEVICE FOR VERY HIGHFREQUENCIESy Donald Harrison Black, London, England, assignor to International Standard Electric Corpora'- tion, New York, N. Y

Application August 29, 1940, Serial No. 354,657

In Great 3 Claims.

This invention relates to electron discharge de-v vices Aof the so-called velocity modulated type.

Briefly the operation of such devices is as follows:

A beam of .electrons of uniform velocity is passed through a gap in a resonator to which is applied the resonant frequency, across the gap, the electrons are accelerated or decelerated according to the phase of the oscillations at the time at which they pass.r After In passing leaving this resonant system,`or modulator, the

electrons pass through a eld-free space, and while in this space a certain degree of bunching of the electrons takes place. This is due to accelerated electrons catching up on the slower ones which preceded them through the modulating gap. The bunched electrons then pass through a second resonant system which is in oscillation and the circuit is so arranged that, owing to this bunching, more electrons will be decelerated on passing through the gap than will be accelerated. If such a state of affairs exists, then the energy given up to the second resonant system by the electrons which are decelerated will exceed the energy extracted from it by those which are accelerated, the net result being a gain in energy by the resonant system.

In the known systems, a single beam of electrons is passed through resonators of various types and some difilculty is experienced in obtaining beams of the required magnitude. In the suggestions so far put forward the source of electrons is usually external to the resonators. In the arrangements now proposed, the electron source is partly or completely enclosed by the resonators and some ofthe diliiculties encountered in the formation of beams are largely overcome.

In one aspect the invention resides in an electron discharge device of the velocity modulated type comprising two co-axial cavity resonators of annular cross-section lying one within the other and an electrode system for projecting electrons radially through grids or apertures in the resonator walls.

In another aspect the invention resides in an y electron discharge device of the velocity modulated type wherein two resonant cavities of annular cross-section are deiined by co-axial cylindrical surfaces, an electron source being provided along the axis of the structure for projecting electrons radially through grids or apertures in the cylindrical surfaces. y

These and other further aspects of novelty and invention will hereinafter be pointed out or will become apparent from a reading of the follow- Britain September 13, 1939 (Cl. Z50-27.5)

ing specification in conjunction with the drawing included herewith. In said drawing Fig. 1 is a cross-sectional elevation of an electron discharge' device Aincorr'noiating features of the invention;

Fig. z is a cross-sectional view taken substantially in the kplane of 2-2 in Fig. l; and

Figs. 3 and 4 are further cross-sectional views taken transversely to the plane of Fig. 1,

Referring to Fig. 1, which is a section through the structure a cathode I is surrounded by av series of concentric grids 2, 3, 5, 1` 9, the axis of revolution being X-`X. The grids are represented by dottedlines butin practice would probably be of squirrel cage formation, up from a series of rods. Fig.'2 shows a sectional view across the line 2-2 of Fig. 1. It will be noticed that the rods forming the respective grids lie on radial lines extending from the cathode. This is a preferred arrangement in order to reduce the number lof electrons collected by the grids.

Grid 2 is normally operated at a negative potential with respect to the cathode and its purposeis to control the magnitude of the space current.k Grids 3 and 5 lormrportions oi cylinders and 6 respectively. The spaces between the ends of the cylinders are closed by the annular discs I6 and I9. The two cylinders with their end discs thus form a resonator of the concentric line type. Similarly grids 1 and 9 form portions of the cylinders 8 and I which with the end discs I1 and I8 form a second concentric line resonator. Cylinders 6 and 8 are Joined by two discs placed at the ends of the grid portions as shown. The cylinder I I collects the electrons which pass through the system. A

The electrons in passing from the cathode I to the collector II pass through two resonators. If the inner resonator has oscillations applied to it, the electrons will be velocity modulated as described above. While moving between the field free space between the inner and the outer cylinders, bunching or the electrons will take place and energy will be imparted to the outer resonator. Oscillations set up in the second resonator may be taken ol by means of lead I2 which contacts with the cylinder 8 through a concentric tube I3. Other methods for withdrawing energy from the second resonator are possible.

If the device is to be used as an oscillator, then some of the energy from the outer resonator must be fed back to the inner resonator. One method of carrying this out is shown in Fig. 1 and in Fig. 3 which is a section across the line being made Y 3-3 Fig. 1. An elongated loop of wire Il has 'one limb, in fthe centre of a connecting tube I 5 and theother'limb just outside@ in the wall o! Il. The rounded ends of the '99p project into the inner and outer resonators.v v`'*Ihe coupling between the two resonators displacement of the loop which exposes a greater area of loop in one resonator than in the other.

The permissible-distance between grids!! andy-5 and between grids, 1,' and, 9 speed of the electrons and the frequency of operation. 'I'he time of ilight across these gaps n'iust4 is varied by a lateral dependsk upon the v not exceed a certain fraction of thel period Iof kone A complete oscillation. In some 'cases it ymay be',

found that the grids must be placed closertogether than isdesirable for kthespacing Vbetween the cylinders if these are to form anfefiicient'v resonator. Fig. 4 shows how this may Abe imf byannular discs, said inner and said outer pairs" being coaxial with each spaced annular discs between said inner and outer pairs of cylinders providing a substantially ileldother, a pair of axially :I vfree ,drift/space., generally longitudinally extendproved by replacing the rods with stripsl ofmetal set radially. The could then be placed on the inner cumferences of 1 and 9 respectively. i Y i Foreillcientoperation of such a devicethetwo resonators must be exactlyl in tune, nator may have a xed frequency vand the other may beA tuned by sliding the end -disclsof the inner resonator up and down.

Various methods are available for ensuring that the electron paths are in vacuumifor'example the structure may be wholly enclosedor'parts of the resonators may'form parts of envelope.

an'evacua'ted .What is claimed is: t l

walls of the cylinders' and i0; and outer ciri One reso# `1. An electron ldischarge device including an inner pair of coaxialvsheet-metal cylinders joined at their ends by annular discs, an outer pair `of coaxial sheet-metal cylinders joined at their ends by annular discs. said inner and said outer pairs said cylinders, through said tube into the two cylinders. a' 3. An- .e1ectrcn discharge device including a/ han outer pair of Vcoaxial ing vgrid members provided between said axially spaced annular discs in apertures in each of the wallsofsaid cylinders, a connecting tube between "and a loop ot wire projecting cathode, a grid surrounding/said cathode; inner pairof coaxial sheet-metal cylinders surrounding said grid and joined at their ends yby lanniiva'rdiscs. Sheet'LnietaI/cyIinders joined at theirmends by lannular discs, said in'iierv and said outer pairs beingcoaxial with each other, a pairl of 'axiallyy spacevdynhllflar `discs beteween said t inner and 'o uterfy pairs of 'cylinders' interme-` diatethe endsofuthe cylinders providinga substantially; ficiii-i'mcl .driftgspaceg and generauy i longitudinallyy yextendingI grid, membersjgsubstan'- tially cc'iexten'sivev with Ithe'./cattlcde and' 'provided between said axiallyspaced annular discs iny aper, tufee each wie' wins oran, cylinders., f-

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