CN112490100A

CN112490100A - Direct current ultrafast electron gun with static single lens

Info

Publication number: CN112490100A
Application number: CN202110075671.4A
Authority: CN
Inventors: 李梦超; 刘巧; 李小菊; 陈维; 黄骏; 王兴权; 荣垂才; 袁寿财; 郭勇; 卢秀圆
Original assignee: Gannan Normal University
Current assignee: Gannan Normal University
Priority date: 2021-01-20
Filing date: 2021-01-20
Publication date: 2021-03-12

Abstract

The invention provides a direct current photocathode ultrafast electron gun with an electrostatic single lens, which comprises a cathode, an anode, an electrostatic single lens electrode plate, a ceramic support column, a single lens support ring, a single lens support and the like. The anode is a disc with a through hole in the center and smooth two surfaces. The single-lens electrode plate is of a double-layer disc surface structure with two smooth surfaces and comprises a circular top disc and a circular protruding bottom disc, wherein the diameter of the circular top disc is larger than that of the circular protruding bottom disc, so that a step structure is formed. The center of the electrostatic single-lens electrode plate is provided with a through hole, and the circular edges at the two sides of the through hole are both subjected to rounding treatment. The single lens support is of a double-metal-disc connecting structure, the upper surface of a top disc of the single lens support is subjected to smoothing treatment, and a through hole is formed in the center of the top disc. The single-lens support ring is of a double-ring structure and comprises a top ring and a bottom ring, the inner diameter of the bottom ring is smaller than that of the top ring, so that a step structure is generated inside the bottom ring, and a through hole is formed in the side face of the support ring.

Description

Direct current ultrafast electron gun with static single lens

Technical Field

The invention belongs to the field of ultrafast electron diffraction, and particularly relates to a direct-current photocathode ultrafast electron gun focusing by using an electrostatic single lens.

Background

Ultrafast Electron Diffraction (UED) is a technique for realizing time-resolved pumping detection by using ultrashort pulse laser, and its principle is that the ultrashort pulse laser is divided into two beams by means of light-splitting device, one beam is used for exciting cathode of electron gun to produce probe electron, and another beam is used for pumping reaction zone, and the probe electron can be used for detecting reaction zone in advance or delay by controlling optical path difference of two beams of laser so as to implement time-resolved measurement. The ultrafast electron diffraction technology is developed greatly, and schemes such as transmission diffraction, surface reflection diffraction, shadow and schlieren imaging, ultrafast transmission electron microscope, ultrafast scanning electron microscope and the like are gradually emerged, and the requirements on a detection system are gradually improved. The shadow and schlieren imaging method is applied to plasma dynamics diagnosis to a certain extent, and is expected to be applied to diagnosis of laser inertial confinement nuclear fusion. The direct current photocathode electron gun is just a probe electron source of the ultrafast electron diffraction technology, and is a core part of the technology.

Due to the repulsive force between electrons, the probe electron pulse is broadened during its drift to the sample, increasing the radial radius, resulting in reduced spatial resolution. The magnetic lens can focus the electron pulse, but the electrons in the electron pulse can be caused to rotate perpendicular to the propagation direction, so that a spiral path is generated, and shadow and schlieren imaging in the ultrafast electron diffraction technology is not facilitated. The electrostatic lens focuses the electron pulse with the generated electrostatic field without a spiral path. A magnetic lens and an electrostatic lens may be used in combination for focusing to improve the performance of the ultrafast electron diffraction system.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a direct current photocathode ultrafast electron gun with an electrostatic single lens, which comprises a cathode, an anode and a single lens electrode plate, wherein the cathode, the anode and the single lens electrode plate are determined by an electric field and a particle simulation program result; the device also comprises a ceramic support column, a single lens support ring and a single lens bracket for fixedly mounting the components.

The anode is a disc with both smooth surfaces, and the center of the disc is provided with a first through hole with the diameter of 0.2 mm; the single lens electrode board is double-deck quotation structure, including circular top dish, circular protrusion chassis, smooth processing is all done on circular top dish and circular protrusion chassis surface, circular top dish is bigger than circular protrusion chassis diameter, thereby the single lens electrode board dorsal part forms first stair structure, there is the trompil single lens electrode board side, open at single lens electrode board center has 4mm diameter second through-hole, the round edge in second through-hole both sides all is radius angle processing, chamfer radius 2 mm.

According to the simulation result of the electronic pulse computer program, the electric field is required to be symmetrically distributed, and the electronic gun is provided with a mounting structure which specially ensures coaxial symmetry and comprises a ceramic support column for fixing the cathode, a single lens support ring for fixing the electrostatic single lens electrode plate and a single lens support for fixing the anode, the single lens electrode plate and the single lens support ring.

The single lens support is of a double-metal-disc connecting structure, the upper surface of a top disc of the single lens support is subjected to smoothing treatment, and a third through hole with the diameter of 0.2mm is formed in the center of the top disc. The support ring is of a double-ring structure, the double-ring structure comprises a top ring and a bottom ring, the inner diameter of the bottom ring is smaller than that of the top ring, so that a second step structure is generated inside the support ring, and through holes are formed in the side face of the support ring.

According to the direct current ultrafast electron gun with the electrostatic single lens, preferably, the anode circular disk has a diameter of 80mm and a thickness of 1mm, the single lens circular top disk has a diameter of 70mm and a thickness of 2mm, and the single lens circular protruding bottom disk has a diameter of 60mm and a thickness of 2 mm. The outer diameter of the top ring of the support ring is 80mm, the inner diameter of the top ring of the support ring is 70mm, the outer diameter of the bottom ring of the support ring is 80mm, and the inner diameter of the bottom ring of the support ring is 60 mm. The outer diameters of the top disk and the bottom disk of the single lens support are both 80 mm.

According to the direct current ultrafast electron gun with electrostatic einzel lens of the present invention, preferably, after installation, the back side of the anode circular disk is 4mm from the top circular disk surface of the einzel lens, and the surface of the einzel lens circular convex bottom disk is 4mm from the top circular disk upper surface of the einzel lens holder.

The fixing mode of the electron gun ensures the uniform and symmetrical distribution of the electric field, ensures the realization of the acceleration and convergence of the electron pulse, reduces the volume of the device and is convenient to transplant to other devices. The electrostatic single lens can be used in combination with the magnetic lens for focusing, the adjustment of the spatial resolution is more flexible, and the experimental function is expanded.

Drawings

Embodiments of the invention are further described below with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of the inner electron gun structure cut along the central axis Z in the X and Y directions of the peripheral cavity and with one quarter of the cavity removed;

FIG. 2 is a perspective view of a disassembled structure of an electron gun according to an embodiment of the present invention;

FIG. 3 is a perspective view of an electrostatic singlet electrode plate of an electron gun and a support ring thereof according to an embodiment of the invention;

FIG. 4 is a perspective view of an electrostatic singlet lens holder according to an embodiment of the invention;

FIG. 5 is a simulation diagram of potential distribution of an electrostatic single lens;

FIG. 6 shows the particle simulation results of the focusing effect of the probe electron pulse under the single lens of the present invention.

Detailed Description

For the purpose of promoting a better understanding of the objects, features and advantages of the invention, reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout the several views. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

For convenience of description of the drawing, a coordinate system is drawn in fig. 1, in which the Z-axis coincides with the central axis of the electron gun.

Fig. 1 is a view of the electron gun structure with one quarter of the vacuum chamber 9 around the electron gun broken away in the X and Y directions along the central axis Z shown. FIG. 2 is a perspective view of the electron gun in a disassembled configuration. The electron gun mainly comprises a cathode 1, an anode 2, a cathode fixing ceramic support column 3, a single lens support ring 4, an electrostatic single lens electrode plate 5, an electrostatic single lens support 6, a cathode vacuum electrode 7, a single lens vacuum electrode 8, an electron gun vacuum chamber 9, a single lens support flange 10 and a cathode support flange 11. The cathode 1 is externally connected with a negative high-voltage power supply through a vacuum electrode 7, and the electrostatic single-lens electrode plate 5 is externally connected with a focusing control power supply through a vacuum electrode 8. The incident laser 13 is incident into the cathode through the laser window 12 to excite probe electrons.

The cathode 1 of the electron gun has an axisymmetric structure, the whole body is a hollow metal cylinder, the top is a structure similar to a small bell, the center of the top of the small bell structure is a circular bottom surface, an arc-shaped connecting surface is arranged between the circular bottom surface and the side surface of the hollow cylinder, the center of the bottom of the cathode is provided with a light through hole 1.1, and four through holes 1.2 are distributed beside the light through hole 1.1.

The positive pole 2 is the smooth disc of two sides all polishing, and disc diameter 80mm, thick 1mm open at the center has a diameter 0.2 mm's through-hole 2.1 (first through-hole).

The center of the ceramic support 3 is provided with a through hole 3.1 which is a laser channel, and four through holes 3.2 are distributed beside the through hole 3.1. The cathode is fixed on the ceramic support 3 through the hole 1.2, the ceramic support 3 is fixed on the supporting flange 11 through the hole 3.2, and the center of the flange 11 is provided with a light through hole 11.1.

Fig. 3 is a perspective view of the electrostatic single-lens electrode plate 5 and its supporting ring 4, wherein the electrode plate 5 includes a circular top plate 5.4 and a circular protruding bottom plate 5.3. The top disk 5.4 has an outer diameter of 70mm and a thickness of 2mm, and the bottom disk 5.3 has an outer diameter of 60mm and a thickness of 2 mm. The whole electrode plate 5 is machined from a whole metal, and the disc surfaces on the two sides are polished smoothly. The top disk 5.4 is larger in diameter than the bottom disk 5.3, resulting in a step structure 5.6 behind the electrode plate 5 (said first step structure). The side of the electrode plate 5 is provided with an electrode connecting hole 5.5, and the center is provided with a through hole 5.1. The diameter of the through hole is 5.1 mm, the edges of the two sides are both provided with round chamfers 5.2 (marked in figure 5), and the radius of the chamfers is 2 mm.

Support ring 4 is two ring structures, including top ring 4.1, end ring 4.2, and for guaranteeing the straightness, whole support ring 4 is processed by monoblock ceramic and is come. The top ring 4.1 has an outer diameter of 80mm, an inner diameter of 70mm, the bottom ring 4.2 has an outer diameter of 80mm and an inner diameter of 60mm, since the inner diameter of the bottom ring 4.2 is smaller than that of the top ring 4.1, resulting in a stepped structure 4.3 (the second stepped structure). The side surface of the support ring 4 is provided with a through hole 4.4. When the electrode plate 5 is installed, the electrode plate is placed inside the support ring 4, and the step structure 5.6 and the step structure 4.3 are mutually embedded. The electrode connecting hole 5.5 is aligned with the through hole 4.4, and the electrode wire of the vacuum electrode 8 is inserted into the two holes, so that the electrode 8 is connected with the electrode plate 5, and the electrode plate 5 and the support ring 4 are fixed.

Fig. 4 is a perspective view of the single lens holder 6, in which the holder 6 is a bimetal disc connection structure, the diameters of the discs on both sides are both 80mm, and the upper surface of the top disc is smoothed. The center of the top disk is provided with a through hole 6.1 (the third through hole) with the diameter of 0.2mm, and the outer side of the through hole 6.1 is provided with 4 threaded holes 6.2 for fixing the support ring 4. The center of a disk at the bottom of the support 6 is provided with a through hole 6.4 which is an electronic pulse channel, 4 through holes 6.3 are arranged around the through hole 6.4, and the support 6 can be fixed on the support flange 10 through the through holes 6.3 by bolts. The center of the supporting flange 10 is provided with a through hole 10.1, and the back of the outer side of the supporting flange is provided with a flange knife edge which can be connected with other devices.

In order to further optimize the surface electric field distribution and ensure the surface smoothness, the surfaces of the cathode 1, the anode 2, the single-lens electrode plate 5 and the single-lens bracket 6 are subjected to mechanical rough polishing, electrolytic polishing, manual fine polishing and high-vacuum cleaning, so that the surface smoothness reaches the micron order.

Assembling an electron gun: the cathode 1 is fixed on the ceramic support 3 through the through hole 1.2, the ceramic support 3 is fixed on the support flange 11 through the through hole 3.2, the flange 11 is installed on one side of the cavity 9 close to the incident laser 13, and the laser window 12 is installed on the outer side of the flange 11. The anode 2 is fixed on the surface of a top ring 4.1 of the support ring 4, and the single lens electrode plate 5 is placed on a step 4.3 inside the support ring 4. The support ring 4 is fixed to a top disc of a bracket 6, the bracket 6 is fixed to a support flange 10, and the support flange 10 is mounted to the other side of the chamber 9. The anode 2, the single-lens electrode plate 5 and the top disk of the bracket 6 jointly form an electrostatic single lens of the electron gun, wherein the back surface of the anode 2 is 4mm away from the surface of the top disk 5.4 of the electrode plate 5, and the surface of the bottom disk 5.3 is 4mm away from the surface of the top disk of the bracket 6.

The electron gun works: laser 13 enters the cavity through the cavity laser window 12 and the through hole 11.1, then enters the cathode through the through hole 3.1 of the ceramic support and the cathode through hole 1.1, and excites the metal film on the circular top surface of the cathode to generate electronic pulse. The generated electronic pulse is accelerated by the electric field between the cathode 1 and the anode 2 and then passes through the anode central through hole 2.1, the electrode plate through hole 5.1 and the bracket through hole 6.1. The electric field among the anode 2, the electrode plate 5 and the disc at the top of the bracket 6 converges the electronic pulse. The electron pulse then passes through the through-hole 6.4 and finally leaves the chamber through the through-hole 10.1.

Fig. 5 is a simulation diagram of the potential distribution of the electrostatic single lens, wherein the anode potential is 0V, the disc potential at the top of the bracket 6 is 0V, the electrostatic single lens electrode plate 5 is-10000V, and the relevant part size is already described above.

Fig. 6 shows the simulation of the electron pulse under the present design using a particle simulation program, where Distance on the horizontal axis is the Distance from the cathode surface in meters and Radius on the vertical axis is the Radius of the electron pulse. The initial radius of the electron pulse was 50 microns and the initial radial diffusion velocity was set to 0. The accelerating voltage between the cathode and the anode was-100 kV. The approximate position of the electrostatic singlet is indicated by the straight dashed line AA' in fig. 6. In the graph, the electron radius curve is marked with V = -15000 and N =100000, which means that the simulation parameters adopted by the result are that the voltage on the single lens electrode 5 is-15000V, and the number of electrons in the electron pulse is 100000. Similarly, the point-break curve is marked with V = -10000, N =10000, which indicates that the simulation parameter adopted by the result is that the voltage on the single lens electrode plate 5 is-10000V, and the number of electrons in the electronic pulse is 10000. As can be seen from the figure, the electrostatic single lens in the invention has a converging effect on the electron pulse.

It should be noted that the size and configuration mentioned in the present invention are only suitable for a certain application scenario, and are not necessarily the optimal configuration for other applications in various situations, so that in order to design and apply the electron gun, it is necessary to perform specific analysis on specific situations, and then obtain the design parameters that are most suitable for the application scenario by using electric field and particle program simulation. The dimensions and configurations referred to herein may be used as a reference for related scientific research and design applications.

Although the present invention has been described by way of preferred embodiments, the present invention is not limited to the embodiments described herein, and various changes and modifications may be made without departing from the scope of the present invention.

Claims

1. A DC ultrafast electron gun with electrostatic single lens comprises a cathode, an anode, a single lens electrode plate, a ceramic support, a single lens support ring and a single lens support; the anode is a disc with both smooth surfaces, and the center of the disc is provided with a first through hole with the diameter of 0.2 mm; the single-lens electrode plate is of a double-layer disc structure and comprises a circular top disc and a circular protruding base disc, the surfaces of the circular top disc and the circular protruding base disc are both subjected to smoothing treatment, the diameter of the circular top disc is larger than that of the circular protruding base disc, so that a first step structure is formed on the back side of the single-lens electrode plate, an opening is formed in the side surface of the single-lens electrode plate, a second through hole with the diameter of 4mm is formed in the center of the single-lens electrode plate, round edges on two sides of the second through hole are both subjected to chamfering treatment, and the chamfering radius is 2; the single lens support is of a double-metal-disc connecting structure, the upper surface of a top disc of the single lens support is subjected to smoothing treatment, and a third through hole with the diameter of 0.2mm is formed in the center of the top disc; the support ring is of a double-ring structure, the double-ring structure comprises a top ring and a bottom ring, the inner diameter of the bottom ring is smaller than that of the top ring, so that a second step structure is generated inside the support ring, and a fourth through hole is formed in the side face of the support ring.

2. The ultra fast direct current electron gun according to claim 1, wherein the anode disc has a diameter of 80mm and a thickness of 1mm, the single lens circular top disc has a diameter of 70mm and a thickness of 2mm, the single lens circular protruding bottom disc has a diameter of 60mm and a thickness of 2mm, the support ring has a top ring outer diameter of 80mm, an inner diameter of 70mm, a bottom ring outer diameter of 80mm and an inner diameter of 60mm, and the single lens holder has a top disc and a bottom disc outer diameter of 80 mm.

3. The DC ultrafast electron gun with electrostatic einzel lens of claim 1, wherein said anode circular disk back side is 4mm from said einzel lens circular top disk surface and said einzel lens circular convex bottom disk surface is 4mm from said einzel lens holder top disk top surface when mounted.