ELECTRON BEAM PROJECTOR WITH LINEAR THERMAL CATHODE

Abstract

An electron beam projector with a linear thermal cathode (7) for electron beam heating consists of a beam guide (1) which comprises a deflecting electromagnetic system (2) and accommodates an accelerating anode (3) fixed on it by a posts (10), where anode is connected by a high-voltage insulators (4) through a cathode plate (5) to a cathode assembly (6), that includes the linear thermal cathode (7) fastened in a cathode holders (8), and a focusing electrode (9). The accelerating anode (3) comprises a plate (11) rigidly fastened to it for hermetical separation of the cathode (7) and the beam guide (1) parts of the projector, wherein the common optical axis of a cathode assembly (6) and the accelerating anode (3) is deflected from a beam guide optical axis by an angle a that is equal to 1030.

Claims

1. Electron beam projector with linear thermal cathode for electron beam heating that comprises beam guide, which includes deflecting electromagnetic system, with fastened to beam guide by posts accelerating anode, which is connected by high-voltage insulators through cathode plate to cathode assembly that incorporates linear thermal cathode, fastened in cathode holders, and focusing electrode; accelerating anode incorporating rigidly connected to it plate for hermetical separation of cathode and beam guide parts of the projector, wherein cathode assembly, accelerating anode and beam guide are positioned so that the common optical axis of cathode assembly and accelerating anode is deflected from beam guide optical axis by angle that is equal to 1030.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Technical essence and principle of operation of the invention are explained on examples of implementation with reference to appended drawings.

[0022] FIG. 1 shows the schematic of partial transverse (a) and longitudinal (b) cross-sections of electron beam projector with linear thermal cathode, according to the invention.

[0023] FIG. 2 shows the schematic of partial cross-section of a traditional electron beam projector with linear thermal cathode.

[0024] FIG. 3 shows the graph of operating life of linear thermal cathode at testing in electron beam projector according to the invention, depending on the angle of inclination of optical axis of cathode assembly and accelerating anode relative to optical axis of beam guide at evaporation of metal ingots of Ni-18% Cr-12% Al-0.3% Y of 68.5 mm diameter at 1.5 A current.

[0025] FIG. 4 presents the appearance of working surface of linear thermal cathode after operation in the traditional electron beam projector (a) and in electron beam projector (b) according to the invention, after evaporation of ceramic ingots of ZrO.sub.2-8% Y.sub.2O.sub.3 type of 68.5 mm diameter at 1.6 A current for 32 and 96 hours, respectively.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Electron beam projector with linear thermal cathode (FIG. 1) for electron beam heating is proposed, which comprises beam guide 1, including deflecting electromagnetic system 2, with accelerating anode 3 fastened on beam guide by posts 10, which is connected by high-voltage insulators 4 through cathode plate 5 to cathode assembly 6 that incorporates linear thermal cathode 7, fixed in cathode holders 8, and focusing electrode 9; accelerating anode 3 including rigidly connected to it plate 11 for hermetical separation of cathode and beam guide parts of the projector, wherein according to the invention, the common optical axis of cathode assembly and accelerating anode is deflected from beam guide optical axis by angle that is equal to 1030 degr.

[0027] As is seen from the appended drawings, and the given description, in the proposed design of electron beam projector with linear thermal cathode, unlike the real design of the prototype (FIG. 2), cathode assembly and accelerating anode are positioned at angle to beam guide vertical axis, i.e. their common optical axis is deflected from beam guide optical axis by angle that is equal to 1030 degr.

[0028] The apparatus operates as follows:

At voltage application to electron beam projector from power source, filament current, passing through cathode holders 8 and linear thermal cathode 7, heats it up to the temperature at which thermoelectronic emission occurs. At the same time, high voltage (negative potential) from high-voltage power source is applied to cathode assembly 6. Electrons which flew out from the surface of linear thermal cathode, are accelerated along the optical axis of cathode assembly-accelerating anode in the electric field applied between cathode assembly 6 and accelerating anode 3, which are electrically separated by high-voltage insulators 4. Having passed through accelerating anode, the electron beam moves by inertia along a common optical axis of cathode assembly-accelerating anode, penetrating into beam guide 1 at angle to its optical axis. Deflecting electromagnetic system 2 provides deflection of electron beam trajectory by the required angle, when it leaves the beam guide. Here, the main parameters of the beam (focal spot size, specific power, etc.) and its control along two coordinates remain unchanged.

[0029] Position of linear thermal cathode in the proposed design ensures minimizing the negative impact of ion flow on it and prevents penetration of atoms and molecules of evaporated materials on its surface, when conducting the technological processes of melting and evaporation. This provides an essential (3-3.2 times) extension of service life of linear thermal cathode, and higher stability of electron-optical parameters. The greatest effect of application of the claimed electron beam projector with linear thermal cathode is achieved in the cases when long-term operation of electron beam unit without breaking vacuum in the chamber or thermal cathode replacement is required in the processes of melting and evaporation in the atmosphere of reactive gases, for instance oxygen.

Example 1

[0030] Electron beam projector of PE-123 type of 60 kW power with standard linear thermal cathode (tungsten plate of 10030.6 mm size) was mounted in electron beam unit of UE-207 type and was used for evaporation of ingots of MCrAlY alloy (Ni-18% Cr-12% Al-0.2% Y) of 68.5 mm diameter, placed into water-cooled copper crucible of 70 mm diameter. Distance from beam guide plane to crucible surface was 680 mm. Angle of deflection of common optical axis of cathode assembly and accelerating anode relative to beam guide optical axis changed in the range from 0 to 30. Pressure of residual gases in the unit work chamber during ingot evaporation was on the level of 210.sup.2 Pa, accelerating voltage was 20 kV, evaporation beam current was 1.5 A.

[0031] Time of linear thermal cathode operation at evaporation current was recorded, testing was stopped after change (violation) of electron beam shape, at which conducting the evaporation process became impossible.

[0032] Results of performed testing, presented in FIG. 3, show that maximum extension of linear thermal cathode life is achieved at angles of deflection of common optical axis of cathode assembly and accelerating anode relative to beam guide optical axis in the range of 2025.

Example 2

[0033] Electron beam projector of PE-123 type of 60 kW power with standard linear thermal cathode (tungsten plate of 10030.6 mm) was mounted in electron beam unit of UE-202 type and was used for evaporation of ceramic ingots of ZrO.sub.2-8% Y.sub.2O.sub.3 type of 68.5 diameter, placed into water-cooled copper crucible of 70 nm diameter.

[0034] Angle of deflection of common optical axis of cathode assembly and accelerating anode relative to beam guide optical axis was equal to 20, angle of deflection of electron beam from electronic optical axis of beam guide at its exit from beam guide was also equal to 20. Residual gas pressure in the unit work chamber during ingot evaporation was on the level of 510.sup.2 Pa, accelerating voltage was 20 kV, beam current for evaporation was 1.6 A. During evaporation, oxygen in the quantity of approximately 200 cm.sup.3/min., was supplied into the unit work chamber. Recorded average time of operation of linear thermal cathode of electron beam projector at this current was 95 hours. Testing was interrupted in connection with deterioration of beam geometrical parameters, making stable evaporation impossible.

[0035] Used as basic values for comparison were the results of similar testing of standard linear thermal cathode of the same dimensions of traditional electron beam projector of PE-123 type, wherein optical axis of cathode assembly, accelerating anode and beam guide coincided, and which was mounted in electron beam unit UE-202 (positions of all tested guns in UE-202 unit and all technological parameters of ingot evaporation were identical).

[0036] Recorded average time of operation of linear thermal cathode of traditional electron beam projector was 30 hours; testing was interrupted in connection with deterioration of beam geometrical parameters, making stable evaporation impossible.

[0037] Appearance of linear thermal cathodes after testing of traditional electron beam projector and claimed electron beam projector is shown in FIG. 4. A characteristic feature of damage of the surface of linear thermal cathode of traditional electron beam projector is erosion damage in thermal cathode central zone and deposition of evaporation material (zirconia-based ceramics) on its surface. Surface of linear thermal cathode of electron beam projector, which is claimed, had no traces of evaporation material, just a slight impact of ion bombardment was observed along thermal cathode surface.

[0038] Above-mentioned positive effect is achieved owing to positioning of cathode assembly and accelerating anode so that their common electronic optical axis is deflected at an angle to electronic optical axis of beam guide, so that the surface of linear thermal cathode is removed from the zone, wherein intensive ion bombardment and deposition of evaporation materials are observed.