US2171214A - Secondary electron emitting screen tube - Google Patents

Description

ug- 29, 1939- J. L. H. JONKER ET A1.

SECONDARY ELECTRON EMITTING SCREEN TUBE Filed June 22; 1957 JOHAN LH. IgA/m51?, EDW'TH. LOPP.

A RIANUS J.W.M. VAN OVERBEEK mmw ATTORNEY Patented Aug. 29, 1939 UNITED STATES PATENT OFFICE Johan Lodewijk Hendrik Jonker, Edmund H. LDP. and Adrianus J. W. M. van Overbeek,

Netherlands Netherlands, assignors to N. V. Philips Gloeilampenfabrieken,

Eindhoven,

Application June 22, 1937, Serial No. 149,581

In the Netherlands June 22, 1936 3 Claims.

'I'he invention relates to electron discharge tubes having an electrode system including a socalled secondary emission electrode which is an electrode having a surface capable of readily emitting secondary electrons when bombarded with primary electrons.

'Ihe principal object of the invention is to provide a simple and eilicient tube of this type. To this end the construction of such a tube is considerably simplified by utilizing part of an accelerating electrode as a secondary emission electrode, preferably by coating the part with a material such as caesium oxide, which readily emits secondary electrons.

In one very emcient embodiment of the present invention the side of the acelerating electrode turned toward the cathode acts as a screen, and the other side, which is coated with a material which readily emits secondary electrons, acts as a secondary emission electrode. It is also feasible to utilize as a secondary electron emitter an extension of the accelerating electrode located either in alignment with the electrode or secured to it at an angle.

The invention will be explained more fully with reference to the accompanying drawing in whichl Figure 1 shows diagrammatically and in cross section a form of construction of an electrode system in which the secondary electron emitter is an extension of the accelerating electrode at an angle to the main part of the electrode and Figure 2 similarly showsta modification in which the side of the accelerating electrode away from the cathode is bombarded to emit secondary electrons.

Figure 1 shows a tube having an indirectly heated cathode I, which consists of a tubular cathode inside of which is an insulated heater. A duplex control element 2 normally biased slightly negative and comprising two solid metal sheets mounted parallel to each other on opposite sides of the cathode tends to concentrate the discharge from the cathode into two electron streams flowing in diametrically opposite directions from the cathode and modulated by a signal voltage impressed on the control element. A duplex accelerating electrode 3 comprising two sheets of solid sheet metal parallel to and outside of the control element cooperates with the control element to form a kind of electron gun which delivers the electron streams at the desired velocity. Each sheet of the accelerating electrode has an elongated portion parallel to the control element and a projection or part 4 set at an angle to the elongated portion and projecting into the (Cl. Z50-174) path of the electron streams, which ow lengthwise of the elongated portions of the laccelerating electrode. The surface of the projection 4 facing the cathode is treated to have high secondary electron emissivity, preferably by being coated with some material such as caesium oxide which readily emits secondary electrons when bombarded by primary electrons. 'I'he free end of the projection 4 from one sheet of the accelerating electrode is spaced a suilcient distance from the adjacent end of the other sheet of the accelerating electrode to leave an unobstlucted gap in front of the treated surface of the projection. An anode 5 mounted to one side oi the accelerating electrode opposite this gap faces the treated surface of the projection 4. The primary electrons flowing from the cathode lengthwise of the elongated portion of the accelerating electrode strike the projection 4 with sumcient velocity to cause a copious emission of secondary electrons, which then ow directly through the unobstructed gap to the anode 5.

In the modication shown in Figure 2 the indirectly heated cathode I is partly surrounded by a duplex control element 6 and a duplex accelerating electrode l, both comprising solid metal sheets on opposite sides of the cathode and in plane parallel relation as in Figure 1. In this modification that side of the accelerating electrode which is turned away -from the cathode is treated with some material such as caesium oxide to enable it to emit secondary electrons readily when struck by primary electrons. A flat apertured anode 8 is mounted outside and opposite the treated facevof the accelerating electrode. vThe electron stream from the cathode I is constrained to follow a curved path, as shown by the arrows, past the end of the accelerating electrode and through the apertured anode 8 to impinge upon the treated face of the accelerating electrode, causing the emission of secondary electrons which ow from the treated face to the apertured anode. The electron stream may be caused to follow the curved path shown by the arrows in various ways, preferably by an auxiliary electrode 9 mounted beyond the end of the accelerating electrode and in alignment with the electron gun formed by the control element and the accelerating electrode, the auxiliary electrode 9 being maintained at a potential, preferably zero or slightly negative, which will produce in the tube an electrostatic eld of such conguration that the electronswill follow the curved path shown from the cathode around the end of the accelerating electrode and through the apertured anode to the treated outer face of the accelerating electrode.

I claim:

1. An electron discharge device comprising a cathode, an accelerating electrode comprising an elongated sheet metal strip bent transversely of its surface to form two portions at an angle to each other and mounted with one portion adjacent said cathode and alongside the path of discharge from said cathode and the other portion extending across the path of said discharge, the surface of said other portion facing said cathode having high secondary electron emissivity, an anode adjacent said other portion of said accelerating electrode, and means for focusing the discharge from said cathode to said anode into an electron stream which impinges on said other portion of said accelerating electrode.

2. An electron discharge tube comprising a rectilinear cathode, a unipotential electrode adjacent said cathode comprising a pair of conductors mounted on opposite sides of and parallel to said cathode, an elongated unipotential accelerating electrode comprising a pair of parallel metal sheets on opposite sides of and parallel to said unipotential electrode and spaced to provide a passage, one of said sheets extending beyond the end of the other sheet and having a bent projecting portion extending across`said passage and forming a gap between the end of said projecting portion and said end of the other sheet, said projecting portion having on the side toward said cathode a surface of high secondary electron emissivity, and an anode mounted adjacent said gap and exposed through said gap to said surface.

3. An electron discharge tube comprising a cathode, beam forming electrodes parallel to and on opposite sides of said cathode, an accelerating electrode comprising a pair of metal sheets mounted on opposite sides of said cathode outside said beam forming electrodes and providing a passage for an electron beam, each of said sheets extending at one end beyond the corresponding end of the other sheet and having a bent projecting portion extending across said passage and forming a gap between the end of said projecting portion and said end of the other sheet, each of said projecting portions having on the side toward said cathode a surface of high secondary electron emissivity, and an anode coxnprising a pair of plates, one mounted adjacent one of said gaps and the other adjacent the other gap and both exposed through said gaps to said surfaces.

JOHAN LODEWIJK HENDRIK JONKER.

EDMUND H. LPP.

ADRIANUS J. W. M. vm OVERBEEK,

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