High-brightness hot cathode electron gun

Abstract

The high-brightness hot cathode electron gun comprises an emitter, a conductor, a cathode electrode, a heater electrode, a heat screen and a gate electrode, the heat screen is provided with an electron emitting hole, the electron emitting hole is in contact with the emitter to form electric connection, the outer end of the heat screen is connected with the cathode electrode, the conductor is located on the inner side of the heat screen, and the gate electrode is located on the inner side of the heat screen. The emitter is electrically connected with the heater electrode through the electric conductor, heating current forms a loop in the heater electrode, the electric conductor, the emitter, the heat screen and the cathode electrode, and the gate electrode is located on the outer side of the heat screen, is spaced from the cathode electrode and forms an electric field. According to the utility model, heating is realized through local resistance control at the contact positions of the emitter, the heat screen and the conducting rod, and heat is conducted to the emitter. As transverse magnetic field components generated by the current flowing through the emitter are mutually counteracted, the divergence of electrons on the surface of the cathode is greatly reduced, and the brightness of the electrons is improved.

Description

Technical Field

[0001] The utility model belongs to the field of industrial equipment based on particle accelerators, and particularly relates to an electron gun with a high-brightness electron beam based on thermionic emission. Background Art

[0002] The microfocus X-ray tube is a key device for high-performance X-ray imaging and is widely used in the fields of semiconductor and new energy detection. In order to achieve a microfocus X-ray, the electron gun in the X-ray tube needs to provide a high-brightness initial electron beam.

[0003] Currently, the electron guns used in microfocus X-ray tubes are mainly reserve-type thermionic cathode electron guns and field emission cathode electron guns. Due to the poor stability of the field emission electron gun, its service life is limited when continuously used on the production line for a long time. Therefore, currently, the electron gun with a reserve-type thermionic cathode for assembling a microfocus X-ray source is widely used. The structure of the reserve-type thermionic cathode is as Figure 1 , in which a high-temperature metal foil is used to integrate the emitter and the heater. The tungsten wire in the heater is heated, and the temperature of the emitter is raised to more than 1000 °C through heat transfer by compacted ceramic powder, so as to emit thermoelectrons. The electrons are accelerated by the electric field between the cathode and the grid electrode and then enter the high-voltage acceleration gap. The problems existing in this thermionic cathode electron gun are as follows:

[0004] First, when using a helical tungsten wire as the heat source of the thermionic cathode, a transverse magnetic field will be generated when the current flows through the vicinity of the emitter. Under the action of the transverse magnetic field Bx, the transverse momentum py of the electron beam in the other direction will increase. For a 3-mm cathode, the transverse magnetic field causes the emittance of the electron beam to increase by about 1 time. This effect is more significant for a small-area cathode; the larger the emittance, the lower the brightness; and the lower the brightness, the more difficult it is to focus.

[0005] Second, the preparation process flow of the traditional reserve-type cathode structure is complex. It is necessary to prepare a heater, and the power output by the tungsten wire heating power supply needs to go through Joule heat, multi-layer heat conduction, interface thermal resistance, and thermal radiation. The physical process from the power supply output power to electron emission is long, which is not conducive to the intelligent constant current of the electron gun.

[0006] Finally, due to the long preparation process of the traditional reserve-type thermionic cathode electron gun and the high cost, the cost of the electron gun accounts for about half of the cost of the entire X-ray tube.

[0007] Therefore, it is urgent to develop a high-brightness thermionic cathode electron gun and a microfocus X-ray tube with high cost performance and simple structure. Summary of the Utility Model

[0008] In view of the above problems existing in the prior art, the utility model provides a high-brightness thermionic cathode electron gun based on thermionic emission.

[0009] To achieve the above object, the present utility model provides the following technical solutions:

[0010] A high-brightness hot cathode electron gun includes an emitter, a conductor, a cathode electrode, a heater electrode, a heat shield, and a grid electrode. The heat shield is provided with an electron emission hole, and the electron emission hole is in contact with the emitter to form an electrical connection. The outer end of the heat shield is connected to the cathode electrode. The conductor is located inside the heat shield. The emitter is electrically connected to the heater electrode through the conductor. A heating current forms a loop in the heater electrode, conductor, emitter, heat shield, and cathode electrode. The grid electrode is located outside the heat shield, is spaced from the cathode electrode, and forms an electric field.

[0011] Further, the conductor is an elastic conductive voltage block.

[0012] Further, the conductor includes a conductive rod, a conductor body, and a conductive slider. One end of the conductive rod is connected to the emitter, and the other end is connected to the conductive slider. The conductive slider is slidably disposed on the conductor body, and a preloading elastic member is disposed between the conductive slider and the bottom surface of the conductor body.

[0013] Further, the bottom surface of the conductor body is a detachable mounting block.

[0014] Further, an annular stepped groove is provided on the upper edge of the emitter, and the electron emission hole of the heat shield overlaps on the stepped surface of the stepped groove.

[0015] Further, one end of the conductive rod is connected to the bottom surface of the emitter.

[0016] Further, the cathode electrode is in contact connection with the heat shield by a clamping method.

[0017] Compared with the prior art, the beneficial effects of the present utility model are:

[0018] In the high-brightness hot cathode electron gun of the present utility model, the cathode is fixed by a pressure rod and an emitter. The current flows into the cathode from the conductive rod and then flows out through the annular heat shield. Heating is achieved through local resistance control at the contact positions of the emitter, heat shield, and conductive rod and is conducted to the emitter. Since the transverse magnetic field components generated by the current flowing through the emitter cancel each other out, the divergence of electrons on the cathode surface is greatly reduced, thereby improving the brightness of the electrons. Description of the Drawings

[0019] Figure 1 is a schematic structural diagram of an existing reserve hot cathode electron gun;

[0020] Figure 2 is a schematic structural diagram of the high-brightness hot cathode electron gun of the present utility model;

[0021] Figure 3 It is a schematic structural diagram of a high-brightness hot cathode electron gun in the embodiment;

[0022] Figure 4 It is a side view of the principle of the direct heating method of the present utility model;

[0023] Figure 5 It is a top view of the principle of the direct heating method of the present utility model.

[0024] Markings in the figure: 1 - grid electrode; 2 - heat insulation screen; 3 - cathode electrode; 4 - emitter; 5 - heater electrode; 6 - heating current; 7 - ceramic powder; 8 - heater; 9 - tungsten wire; 10 - heating power supply connection; 11 - conductive rod; 12 - conductive slider; 13 - pre-pressing elastic member; 14 - pressing block; 15 - conductive body main body; 16 - elastic conductive pressing block. Specific implementation manners

[0025] The present utility model will be further described in detail below with reference to the accompanying drawings.

[0026] The present utility model improves the existing reserve-type hot cathode structure and provides a high-brightness hot cathode electron gun based on hot cathode emission.

[0027] The structure of a high-brightness hot cathode electron gun of the present utility model is as Figure 2 shown, mainly including an emitter 4, a conductive body, a cathode electrode 3, a heater electrode 5, a heat insulation screen 2, and a grid electrode 1. Among them:

[0028] The heat insulation screen 2 adopts an annular cover structure. An electron emission hole is provided at the top of the heat insulation screen 2. The outside of the heat insulation screen 2 is connected to the cathode electrode 3. In this embodiment, it is preferably that the hot cathode adopts a simple clamping contact to ensure the reliable contact between the heat insulation screen 2 and the cathode electrode 3. The cathode electrode 3 of the present utility model includes but is not limited to a reserve-type cathode and a boride cathode.

[0029] The grid electrode 1 is located outside the heat insulation screen 2. An electron emission hole is also provided on the grid electrode 1. The position of the electron emission hole on the grid electrode 1 corresponds to that on the heat insulation screen 2. The grid electrode 1 and the cathode electrode 3 are parallel to each other, and an electric field for emitting hot electrons is formed between them.

[0030] The emitter 4 is arranged at the electron emission hole of the heat insulation screen 2, and the emitter 4 is in electrical connection with the electron emission hole in contact. In this embodiment, it is preferably to adopt the structure of the emitter 4 as Figure 2 shown, that is, a stepped groove is provided at the upper edge of the emitter 4, and the edge of the electron emission hole of the heat insulation screen 2 overlaps on the step surface of the stepped groove to form an electrical connection.

[0031] The emitter 4 is electrically connected to the heater electrode 5 through a conductive body. The conductive body is located inside the heat insulation screen 2, as Figure 2As shown, the conductor uses an elastic voltage-conducting block 16, which not only has the function of electrically connecting the emitter 4 and the heater electrode 5, but also has a certain elasticity to adjust the magnitude of the pre-pressure. Specifically, in this embodiment, it is preferably adopted as Figure 3 the conductor structure shown, that is, the conductor mainly includes a conductive rod 11, a conductor body 15, and a conductive slider 12. Among them, the upper end of the conductive rod 11 is electrically connected to the bottom of the emitter 4, and the lower end is electrically connected to the conductive slider 12. A chute is provided on the conductor body 15, and the conductive slider 12 is slidably installed in the chute. The conductive slider 12 is electrically connected to the conductor body 15, and a pre-pressure elastic member 13, such as a compression spring, is provided between the bottom surface of the conductive slider 12 and the conductor body 15. In order to adjust the pre-tightening force of the pre-pressure elastic member 13, the bottom surface of the conductor body 15 can be divided into parts, for example, it is set as a detachable pressing block 14. The use of the pre-pressure elastic member 13 can ensure the close contact between the emitter 4 and the conductive rod 11.

[0032] During use, the cathode electrode 3 and the heater electrode 5 are respectively connected to the heating power supply through the heating power supply wiring 10, and the heating current 6 forms a loop in the heater electrode 5, the conductor, the emitter 4, the heat shield 2, and the cathode electrode 3. The temperature of the emitter is increased by heat transfer through the conductive rod 11 until thermoelectrons are emitted, and the electrons are extracted under the acceleration of the electric field between the cathode electrode and the grid electrode.

[0033] As Figures 4-5 shown, the current vector I flowing from the conductive rod through the emitter to the heat shield can be decomposed into Ir and Iz, where Iz forms an angular magnetic field B θ , and Ir generates an axial magnetic field component B z and an angular magnetic field component B θ . Among them, due to the coaxial distribution of the current, the axial magnetic field components cancel each other out after positive and negative cancellation. Therefore, there is only an angular magnetic field B θ on the surface of the emitter with the coaxial current structure adopted by the present invention.

[0034] The interaction between the transverse magnetic field and the longitudinal velocity of the electrons will generate a transverse velocity in the orthogonal direction:

[0035] For the traditional heater structure, the main transverse magnetic field on the cathode surface is Bx (assuming the direction of the central heating wire is arranged along the y direction), and the increment of the electron transverse momentum is:

[0036] Δp y =F y Δt = qv z B x Δt

[0037] For the structure of the present invention, the main magnetic field on the cathode surface is B θ , and the increment of the electron transverse momentum is:

[0038] Δp r = F r Δt = qv z B θ Δt

[0039] Since the heating current is distributed over the entire emitter, the magnetic field B at the center surface of the cathode θ is much smaller than the transverse magnetic field B at the center of the cathode using a conventional heater structure x . Therefore, the transverse electron increment Δp caused by the magnetic field on the cathode surface r is also significantly smaller than Δp y . In addition, the transverse Δp of the electron beam r is uniformly distributed at various angles, so the coaxiality is better, which is beneficial to achieving better focusing.

[0040] To ensure reliable contact of the electron gun, the hot cathode uses a simple clamping contact, and an elastic structure is adopted to ensure tight contact between the emitter, the heat shield, and the conductive rod.

[0041] For the cathode with a traditional heater structure, the cathode temperature model is:

[0042] T c = T 0 f c

[0043] For this structure, the cathode temperature model is:

[0044] T c = T 0 f fh f hc f c

[0045] where T c is the temperature of the cathode emission surface, T 0 is the temperature of the Joule heat generating body, f fh is the temperature transfer function from the heating wire to the heater ceramic, f hc is the temperature transfer function from the heater ceramic to the cathode, f c is the temperature transfer function inside the cathode. The temperature transfer function is determined by the specific structure and operating temperature of the cathode.

[0046] It can be seen that the transverse magnetic field components generated by the current flowing through the emitter partially cancel each other out, greatly reducing the divergence of electrons on the cathode surface, thereby improving the brightness of the electrons. Since this structure adopts a direct heating method, the Joule heat and its conduction process are greatly simplified, and the model is simpler when performing feedback modeling, greatly improving the long-life stability of the electron gun.

[0047] To ensure reliable contact of the electron gun, the hot cathode of the present utility model adopts a simple clamping contact, and an elastic structure is used to ensure close contact between the emitter, the heat shield and the conductive rod. With this simple preloading structure, the joule heat and its conduction process are greatly simplified, and the model is simpler when performing feedback modeling, thus greatly improving the long-life stability of the electron gun.

[0048] Since the traditional heater structure is abandoned, the parts used are all conventional precision parts, and there is no need for complex processes such as heater winding, shaping, and powder sintering. The production cycle and cost of the product are significantly reduced.

[0049] The above are only the preferred embodiments of the present utility model and are not intended to limit the present utility model. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present utility model shall be included within the protection scope of the present utility model.

Claims

1. A high brightness hot cathode electron gun, characterized in that: It includes an emitter, a conductor, a cathode electrode, a thermal electrode, a heat shield, and a gate electrode. The heat shield is provided with an electron emission hole, and the electron emission hole is in contact with the emitter to form an electrical connection. The outer end of the heat shield is connected to the cathode electrode. The conductor is located on the inner side of the heat shield. The emitter is electrically connected to the thermal electrode through the conductor. The heating current forms a loop among the thermal electrode, the conductor, the emitter, the heat shield, and the cathode electrode. The gate electrode is located on the outer side of the heat shield, and is spaced apart from the cathode electrode to form an electric field.

2. A high brightness hot cathode electron gun according to claim 1, characterized in that: The conductor is an elastic conductive voltage block.

3. A high brightness hot cathode electron gun according to claim 2, characterized in that: The conductor includes a conductive rod, a conductive body, and a conductive slider. One end of the conductive rod is connected to the emitter, and the other end is connected to the conductive slider. The conductive slider is slidably arranged on the conductive body, and a pre-stressed elastic member is arranged between the conductive slider and the bottom surface of the conductive body.

4. A high brightness hot cathode electron gun according to claim 1, characterized in that: The bottom surface of the conductor body is a detachably mounted pressing block.

5. A high brightness hot cathode electron gun according to claim 1, characterized in that: The upper edge of the emitter is provided with a stepped groove, and the electron emission hole of the heat insulation screen overlaps the step surface of the annular stepped groove.

6. A high brightness hot cathode electron gun according to claim 3, characterized in that: One end of the conductive rod is connected to the bottom surface of the emitter.

7. A high brightness hot cathode electron gun according to claim 1, characterized in that: The cathode electrode is contact-connected with the heat insulation screen in a clamping manner.

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