DE1005199B - Beam generation system for generating an electron beam with high current density by means of magnetic focusing - Google Patents

Description

GERMAN

The invention is concerned with a beam generating system for the generation of electron beams of high current density with the help of magnetic focusing.

In the construction of beam generating systems for beams of high current density, which are magnetic be focused, it is desirable and in some types, beam propagation even necessary, that the cathode is shielded from the constant axial magnetic focusing field, which together with the discharge vessel, of which the beam generation system forms a part, is used. It is desirable and sometimes necessary that the generated by a beam generating system Electron beam is essentially parallel to the beam axis. They are already magnetic collecting lenses short field length, preferably magnifying lenses for electron optics, consisting of a Collector coil in a completely surrounding, made of highly permeable material jacket, the has an annular gap in its inner part and in which the edges of the in relation to the longitudinal extent the coil forming a narrow gap sheath part tapers to pole shoe-like after the axis and the clear width of the pole shoe ring is in the order of magnitude of the gap height. The gap between the pole pieces of this magnetic converging lens is vacuum-tight with non-magnetic material filled in, and the part of the jacket surrounding the coil which is located inside the coil serves as the tube wall an electron optical device. The arrangements are called short focal length converging lenses used in electron microscopes. For producing an electron beam with a high current density and homogeneous flow, however, they are not suitable. It is also already a beam generation system known, in which the acceleration anode has a pole piece for the magnetic focusing arrangement forms. In these arrangements, the cathode and the focusing electrode are complete enclosed in the pole piece anode, and contact with the rest of the magnetic circuit is made by a disk of ferromagnetic material melted through the casing of the tube manufactured.

Instead of a disc that makes contact with Establishes the magnetic circuit, according to the invention, the cathode and the focusing electrode completely enclosed by the pole piece which forms part of the tube casing. Such a beam generation system is easy to manufacture and can be easily assembled, so that the necessary accuracy in the position of the beam generating electrodes is obtained. The cylindrical

Beam generation system

for generating an electron beam

high current density by means of magnetic

Focus

Applicant:

International Standard Electric
Corporation, New York, NY (V. St. A.)

Representative: Dipl.-Ing. H. Ciaessen, patent attorney,
Stuttgart-Zuffenhausen, Hellmuth-Hirth-Str. 42

Claimed priority:
Great Britain March 20, 1953

Arnold HW Beck, London,
has been named as the inventor

The drical focusing electrode has egg over the emission surface the cathode has an end cap provided with an opening and one between its ends outer circular flange. The magnetic anode disc with a central opening Material lies against an end ring of the generally cylindrical outer ferromagnetic shell Material and fits exactly into this outer shell. An inner cylindrical one with the anode disk connected anode envelope surrounds the focusing electrode and is provided with a protrusion to To fix the cathode and focusing electrode in relation to this anode disk. An annular one Washer of insulation material is between this protrusion and the outer circular flange of the cylindrical focusing electrode to fix the axial position of the cathode and around pressing the anode disk against the end of the outer shell.

The outer ferromagnetic shell is preferably made of a compound that is easy to use Glass can be fused so that the tube can be closed by glass, for example a pressed glass plate and the other end can be fused to a glass envelope of the discharge tube. Be it notes that this beam generating system works well for use with all metallic clad tubes suitable is.

An exemplary embodiment is explained in more detail with reference to the drawing.

609 866/344

Fig. 1 shows a longitudinal section of an embodiment, and

FIG. 2 shows a cross section along the plane H-II of FIG.

The beam generation system 1 consists of an indirect heated cathode 2 with concave emission surface. The cathode 2 is surrounded by a Focusing electrode 3 supported. The upper end, namely the end cap 4 of this cylindrical focusing electrode is provided with a central opening to expose the emission surface of the cathode. Between the ends of the focusing electrode are an outer circular flange 5 and am lower. A further circular flange 6 is arranged at the end. The focusing electrode is in operation during operation 3 at cathode potential and can therefore be connected to this. The anode of the beam generation system consists of the anode disk 7 provided with a central opening made of ferromagnetic Material with which a cylindrical inner anode shell 8 is welded. This surrounds the focusing electrode 3 and is also connected to the Projection 9 provided. An annular disc 10 of insulating material, such as mica, fits just above the top of the focusing electrode 3 and rests against your projection 9. The outer circular flange 5 of the focusing electrode rests against the lower side of the disc 10. In this way is the emission surface the cathode 2 centrally within the inner anode shell and at the appropriate axial distance from the anode disk 7 set. The disk 7 is provided with a central opening 11, the sides of which are preferably are beveled, as can be seen from FIG. The thickness of the anode disk 7 and the position the focusing electrode to the anode is preferably such that a fully space-charge-limited current is drawn from the cathode and the beam through the Anode opening 11 is so> focused that it is essentially parallel to the longitudinal axis of the beam generating system immediately after it emerges from this opening. In most cases the cathode surface is as shown in Fig. 1, concave. The jet generation system can be dimensioned so that it is particularly suited to an electron beam to send out whose electron movement is equal to the Brillouin flux. Based on a cylindrical solid beam (as opposed to an annular beam) is the Brillouin flow through it characterizes that all electrons have the same axial velocity and each electron is on Reason of a constant axial magnetic field in spirals of constant radius around the beam axis move at the same angular velocity so · that the movement of the beam is equal to that of a solid rod that moves around and along its axis. For a cathode with a concave Emission surface requires such a flux that the cathode from the influence of the axial magnetic field is shielded. In the present arrangement this is achieved by the anode disk 7 and the outer shell 12 achieved from ferroinagnetic material. It is known that in order to improve the magnetic shielding, it is more advantageous to use several separate screens made of magnetic material, as a single screen, the thickness of which is the sum of the thicknesses of the individual screens. That's why it is advantageous to make the inner anode sleeve 8 also from ferromagnetic material. If the Anode disk 7 forms a pole piece of the magnetic focusing arrangement, connecting links can be used (Yokes) are connected to the outer sleeve 12 in the usual way. These yokes or links further improve the magnetic shielding of the cathode.

The beam generating system described is well suited to form part of an all-metal tube. Some known means can be used to reduce the pressure between the anode disk 7 and the End ring 13 of the outer shell 12 and also between the circular flange 5 of the focusing electrode the disc 10 and the projection 9 of the inner anode sleeve 8 to maintain. In the one in the figures illustrated embodiment, the outer part 12 is made of a compound which can easily be fused with glass, for example a nickel-iron alloy in a ratio of 50:50. With one end of the outer shell 12 is a glass part 15 fused, which a common. Pressed glass plate 16 with the guide pins 17 carries. One end of a number of pins 18 is with the Insulating washer 14 and the other with the corresponding lead-through pins 17 firmly connected to "the necessary axial pressure to be maintained between the various beam generating electrodes. In The exemplary embodiment is a glass envelope 19 of the discharge vessel from which the beam generating system forms a part, with the end ring of the outer cylinder 12 butt fused.

Since the parts of the beam generation system fit together well, this beam generation system is easy to manufacture, and the necessary critical distances between the. individual electrodes can can easily be achieved with great accuracy.

Claims (17)

PATENT REQUIREMENTS: 1. Beam generating system for generating a Electron beam of high current density by means of magnetic focusing, characterized in that that the cathode and the focusing electrode completely from the - part of the tube envelope forming - pole piece are included. 2. Beam generating system according to claim 1, characterized in that the cylindrical focusing electrode is provided with an end cap, the opening of which is above the emission surface the cathode lies. 3. Beam generating system according to claim 1, characterized in that the cylindrical focusing electrode is provided with a circular flange. 4. Beam generating system according to claim 1, characterized in that the pole piece with a End ring is provided. 5. Beam generating system according to. Claim 4, characterized in that one with a central Anode disk made of ferromagnetic material with an opening against the end ring of the pole piece presses. 6. beam generating system according to claim 5, characterized in that the anode disk exactly in the outer cylindrical shell of ferromagnetic material that forms the pole piece fits. 7. beam generating system according to claim 5, characterized in that with the anode disk an inner cylindrical anode sleeve is firmly connected. 8. jet generating system according to claim 7, characterized in that the inner anode sleeve surrounds the focusing electrode. 9. Beam generating system according to claim 7, characterized in that the inner anode sleeve is provided with a protrusion to the cathode and the focusing electrode with respect to the Define anode disk. 10. Beam generating system according to claim 1 and / or 3 and / or 9, characterized in that that an annular disc of insulating material between the projection and the outer circular flange is arranged. 11. beam generating system according to claim 10, characterized in that this flange against the annular disc and the annular Press the washer against the projection. 12. Beam generating system according to claim 1 and / or 4, characterized in that the of the end of the outer shell remote from the end ring is closed by means of a glass seal. 13. Beam generating system according to claim 1 and / or 12, characterized in that the focusing electrode with a number of rods is firmly connected, the other ends of which are firmly connected to the glass fusion. 14. A beam generating system according to claim 13, characterized in that the rods with the Feedthrough pins of a glass plate of the glass fusing are connected. 15. Beam generating system according to claim 4, characterized in that with your end ring the outer shell a cylindrical glass shell is butt fused. 16. Beam generating system according to claim 1 and / or 7, characterized in that the inner The anode shell is made of ferromagnetic material. 17. Beam generating system according to claim 1 and / or 5, characterized in that the The anode disk is dimensioned so and the cathode and the focusing electrodes so to one another are arranged that under operating conditions a space-charge-limited electron beam is generated by the beam generating system, which is substantially parallel to the beam axis is immediately after leaving the opening of the anode disk. Considered publications:
German patent specification No. 680 284. 1 sheet of drawings © 609 866/344;. V: