阅读说明：本技术 一种适用于超快电子衍射技术的超高压直流电子枪 (Ultrahigh voltage direct current electron gun suitable for ultrafast electron diffraction technology ) 是由 杨靖 胡建波 于 2020-05-08 设计创作，主要内容包括：本发明公开了一种适用于超快电子衍射技术的超高压直流电子枪,该超高压直流电子枪,由高压直流电源、分压电路、阴极和多个阳极组成,且阴极与阳极通过耐高压陶瓷柱固定连接；所述阴极由金属铸造而成,且在正中心穿孔并镶嵌具有通光功能的材料；所述阳极端的个数由所加电压决定。通过上述方案,本发明达到了获得同时具有超亮度和超高时间分辨率的电子探针脉冲,而不会产生明显的时间抖动的目的,具有很高的实用价值和推广价值。(The invention discloses an ultrahigh voltage direct current electron gun suitable for an ultrafast electron diffraction technology, which consists of a high voltage direct current power supply, a voltage division circuit, a cathode and a plurality of anodes, wherein the cathode and the anodes are fixedly connected through high voltage resistant ceramic columns; the cathode is formed by metal casting, a hole is formed in the center of the cathode, and a material with a light-transmitting function is embedded in the hole; the number of the anode terminals is determined by the applied voltage. Through the scheme, the invention achieves the aim of obtaining the electronic probe pulse with super-brightness and super-high time resolution without generating obvious time jitter, and has very high practical value and popularization value.)

1. An ultrahigh voltage direct current electron gun suitable for an ultrafast electron diffraction technology is characterized by comprising a high voltage direct current power supply, a voltage division circuit, a cathode and a plurality of anodes, wherein the cathode and the anodes are fixedly connected through high voltage resistant ceramic columns; the cathode is formed by metal casting, a hole is formed in the center of the cathode, and a material with a light-transmitting function is embedded in the hole; the number of the anode terminals is determined by the applied voltage.

2. The superhigh voltage dc electron gun for ultrafast electron diffraction technology of claim 1, wherein the voltage divider circuit serially divides the voltage with a plurality of super resistors, and the total resistance of the super resistors is not less than 300M Ω.

3. The superhigh voltage dc electron gun for ultrafast electron diffraction technology as set forth in claim 2, wherein the metal of said cathode end is steel or copper, and the diameter of said through hole in the center is 5 mm-20 mm.

4. The superhigh voltage dc electron gun according to claim 3, wherein the material having the light passing function is a white gem coated with a gold film, and the gold film is flush with the cathode surface and has a smooth surface.

5. The superhigh voltage dc electron gun suitable for ultrafast electron diffraction technology as set forth in claim 3, wherein the material having a light-passing function is a material that generates electrons by utilizing a photoelectric effect.

6. The gun according to claim 1, wherein the number of anodes at the anode end increases with increasing voltage, wherein one anode is added for every 90kV increase in voltage.

7. The ultrahigh-voltage direct-current electron gun suitable for the ultrafast electron diffraction technique of claim 6, wherein the anode is a silicon wafer plated with a metal film, and a hole with a diameter of 1mm is formed in the center of the anode.

Technical Field

The invention belongs to the field of ultrafast science, and particularly relates to an ultrahigh voltage direct current electron gun suitable for an ultrafast electron diffraction technology.

Background

Ultrafast Electron Diffraction (UED) is a powerful desktop in-situ probing tool, widely used for the study of lattice kinetics and chemical reaction kinetics with atomic-scale resolution. In principle, the time resolution of the UED depends on the duration of the pump laser, probe electronic pulses, and the time jitter and speed mismatch between them. Considering that the velocity of atomic motion in chemical reactions is about 1000m/s, the time resolution of UED needs to be in the order of hundreds of femtoseconds, so improving the time resolution of pump laser and probe electron pulses is an important direction for UED development. With the development of femtosecond laser technology, the laser system can obtain the laser length shorter than 10 from commercial titanium sapphire laser systemfs pump laser pulses. However, even though there have been recent reports on attosecond electron pulsed beams, how to make the probe electron beam pulse rate up to 100fs remains a challenging task. The brightness of the electron beam pulses is another important indicator in UED detection. This is mainly due to the large number of perfectly uniform ultrathin samples that need to be prepared in the experiments, but this is almost impossible for most solid materials. To enable a single measurement, 10 pulses are required per pulse⁵-10⁶And (4) electrons. However, the strong coulomb repulsion between electrons greatly increases the pulse width of the electron probe as the number of electrons increases, and decreases the time resolution of the UED.

In order to overcome the contradiction between the pulse duration and the brightness of the electronic probe, researchers have proposed several methods in sequence. Using a Radio Frequency (RF) cavity to accelerate the electron beam to MeV magnitude, suppression of space charge effects by relativistic effects is a common approach. By this method, the pulse width of the electron beam may reach below 10 fs. In the non-relativistic case, the RF cavity is used to compress the electron beam generated by the dc photo-electron gun based on the chirp characteristics during the electron beam transmission. By means of a hybrid DC-RF electron gun, researchers obtain electronic pulses below 100 fs. However, the use of RF accelerating cavities can introduce synchronization problems between the RF field and the pump pulses due to phase jitter, making the time resolution of the UED less than ideal and, in addition, leading to less than satisfactory long-term stability of the UED instruments.

A simpler solution is to develop ultra-compact dc photoelectron guns to reduce the time of coulomb force repulsion by shortening the propagation distance between the photocathode and the sample. In 2003, Siwick et al obtained a bright 600-fs electron pulse of 6000 electrons per pulse by a 30keV compact dc gun and first atomic level observations of light induced melting in aluminum, demonstrating the potential of this approach. Since electrons having higher energy travel faster and can reach the sample in a shorter time, the development of a high-voltage compact dc photoelectron gun is an important research direction. In 2015, Waldecker et al reported a 100keV DC photoelectron gun, and simulation results showed that: at a sample position of 10 mm from the cathode (2 mm from the anode), the pulse width can reach 100fs at an electron number of 5000 within an electron pulse. It is not possible to obtain brighter, shorter electron pulses by further increasing the electron energy of the dc electron gun to a sub-relativistic situation, while also avoiding the synchronization problems created by rf photoelectron guns.

N-particles simulations by Sciaini and Dwayne Miller showed that 10 keV DC guns can be used to generate⁴An electron (or 10)⁵One electron) and a spot size of 100 μm, 100fs (or 200 fs). However, in practice, due to the problem of high voltage breakdown, providing such a strong electric field strength in the compressed space between the photocathode and the anode has become difficult to achieve when the voltage exceeds 120 kV.

Disclosure of Invention

In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides an ultra-high voltage dc electron gun suitable for ultrafast electron diffraction technology, which obtains electron probe pulses having both ultra-brightness and ultra-high time resolution without generating significant time jitter

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

an ultrahigh voltage direct current electron gun suitable for an ultrafast electron diffraction technology comprises a high voltage direct current power supply, a voltage division circuit, a cathode and a plurality of anodes, wherein the cathode and the anodes are fixedly connected through high voltage resistant ceramic columns; the cathode is formed by metal casting, a hole is formed in the center of the cathode, and a material with a light-transmitting function is embedded in the hole; the number of the anode terminals is determined by the applied voltage.

Furthermore, the voltage division circuit adopts a plurality of super resistors to divide voltage in series, wherein the total resistance value of the super resistors is not less than 300M omega.

Furthermore, the metal of the cathode end is steel or copper, and the diameter of the through hole in the center is 5-20 mm.

Further, the material with the light passing function is a white gem with a gold film plated on the surface, wherein the gold film is flush with the surface of the cathode, and the surface is smooth.

Further, the material having the light passing function is a material that generates electrons by utilizing a photoelectric effect.

Further, the number of anodes at the anode end increases with increasing voltage, wherein one anode is added for every 90kV increase in voltage.

Specifically, the anode is a silicon wafer plated metal film, wherein a hole with the diameter of 1mm is formed in the center of the anode.

Compared with the prior art, the invention has the following beneficial effects:

(1) the invention can avoid the problem of electric field breakdown caused by particle collision by using a partial pressure acceleration mode, thereby enabling the direct current electron gun to work with electron energy as high as 270keV and electric field intensity as high as 15 MV/m. With such a dc electron gun, it is possible to obtain electron probe pulses having both ultra-brightness and ultra-high temporal resolution without significant temporal jitter. By using such UED of ultra bright, ultra fast and ultra stable electronic pulses, irreversible processes such as chemical reactions can be explored.

Drawings

FIG. 1 is a schematic diagram of the system of the present invention.

FIG. 2 is a schematic structural diagram of a cathode according to the present invention.

FIG. 3 is a schematic structural view of an anode according to the present invention.

FIG. 4 is a simulated electric field generated by the electrode optimization design of the present invention.

FIG. 5 shows the electric field intensity near the surface of each electrode according to the present invention.

FIG. 6(a) is a graph of the relationship between the electron pulse and the laser spot radius according to the present invention.

FIG. 6(b) is a plot of the time resolution as a function of the number of electrons in a single pulse for three laser spot sizes (25, 50 and 100 μm) of the present invention.

In the drawings, the names of the parts corresponding to the reference numerals are as follows:

1-high voltage direct current power supply, 2-voltage division circuit, 3-cathode, 4-anode.

Detailed Description

The present invention is further illustrated by the following figures and examples, which include, but are not limited to, the following examples.