CN109860010B - Method for applying local electric field to inhibit radial oscillation of electron beam - Google Patents

Abstract

The invention relates to a method for inhibiting the radial oscillation of an electron beam by applying a local electric field, namely a method for inhibiting the radial oscillation of an electron beam in a cylindrical drift tube z₀≤z≤z₁In the range, a radial electric field along the-r direction is applied, electrons carry out Larmor cyclotron motion under the constraint of a uniform magnetic field, and electrons pass throughWhen the local electric field is applied to the area, the radial electric field applies work to the electrons to change the radial oscillation of the electron beam, when the electrons enter the local electric field area and are positioned near the peak value of the radial oscillation, and when the electrons leave the local electric field area and are positioned near the valley value of the radial oscillation, the radial electric field along the-r direction applies negative work to the electrons, so that the transverse momentum of the electron beam is reduced, and the aim of inhibiting the radial oscillation of the electron beam is finally fulfilled.

Description

Method for applying local electric field to inhibit radial oscillation of electron beam

Technical Field

The invention belongs to the technical field of beam transmission, and relates to a method for inhibiting radial oscillation of an electron beam by applying a local electric field in a cylindrical drift tube.

Background

Under low guidance field conditions, the electron beam experiences significant radial oscillations as it travels axially in the cylindrical drift tube due to its lateral momentum. When the radial oscillation amplitude is large, the electron beam may bombard the wall of the drift tube, resulting in beam loss. This phenomenon often occurs in low magnetic field O-type high power microwave generating devices, electrons bombarded on the tube wall of the generating device cause strong electromagnetic field vacuum breakdown, even cause the tube wall to be obviously damaged, and seriously affect the normal operation of the generating device. The transverse momentum of the electron beam in the low-magnetic-field drift tube is reduced by adopting a proper method, so that the radial oscillation of the electron beam is inhibited, the problems are favorably alleviated, and the technical support is provided for the efficient and stable operation of the low-magnetic-field O-type high-power microwave generating device.

At present, a great deal of research is being conducted at home and abroad on the transmission characteristics of electron beams in drift tubes under the condition of low guiding magnetic fields. In 1981, a.t. drobot et al studied the effect of transverse velocity in the drift tube on beam transport (a.t. drobot, et al, international Journal of Electronics,1981,51: 354). In 1989, Wang mountain et al, the institute of high-energy electronics, based on the assumption of infinite-length drift tube, studied the motion trajectory of a thin annular electron beam, and obtained that the fast cyclotron motion of electrons is Larmor cyclotron motion around a guide center under the condition of zero-order approximation, and the radial oscillation amplitude of electrons is in an inverse proportion relation to the magnetic field strength (Wang mountain, et al, university of electronic technology, 1989,18: 326). In 2013, a Tan Uygur of the institute of nuclear technology in northwest carries out theoretical research on electron motion on a beam envelope boundary in a drift tube under the condition that an electron beam is considered from an electromagnetic field, and a theoretical expression of the radial oscillation amplitude of the electron beam is obtained (Tan Uygur, a student's academic paper of the institute of nuclear technology in northwest, 2013). These results provide the basic basis for researching the method for restraining the radial oscillation of the electron beam in the low-magnetic field drift tube.

From the viewpoint of the drift tube itself, the conventional methods for suppressing the radial oscillation of the electron beam mainly include the following methods. Firstly, an anode foil is arranged at the front end of the drift tube or at a proper position in the drift tube, and the focusing of electron beams is realized to a certain extent (forest super, et al. strong laser and particle beams, 2009,21: 875; E.M.Totmeniov, et al. IEEE Trans. plasma Sci.2011,39: 1150; Junpu Ling, et al. Phys. plasma 2014,21: 023114). However, the anode foil may be damaged by the electron beam bombardment and easily causes beam current loss, so that it has not been widely used. Secondly, a decreasing guiding magnetic field (doctor's academic paper of national defense science and technology university, 2002) is applied in the drift tube region, which theoretically can reduce the electron transverse momentum, but the gradual reduction of the guiding magnetic field weakens the suppression effect on the electron beam radial oscillation.

Disclosure of Invention

The invention aims to solve the technical problem that under the condition of a low guiding magnetic field, an electron beam can generate obvious radial oscillation due to transverse momentum when the electron beam is axially transmitted in a cylindrical drift tube.

In order to solve the technical problem, the invention adopts a method of applying a local electric field to inhibit the radial oscillation of the electron beam. The specific technical scheme is as follows:

the electron beam passes through a radius of R under the constraint of a uniform axial guidance magnetic field with the magnetic induction intensity of B_dThe guide center of the motion of the cylindrical drift tube is radial displacement R₀And has r_L<R₀，R₀+r_L<R_dWherein r is_LElectron larmor radius of gyration; at z₀≤z≤z₁The absolute value of the applied electric field intensity on the electron motion path in the range is E_rThe electric field direction is along the-r direction; radial electric field region start position z₀Axial position z of nearest neighbor electron radial oscillation peak_maxThe deviation of (a) satisfies:

|z₀-z_max|≤0.15v_zT (1)

radial electric field region end position z₁Axial position z closest to the radial oscillation valley of the electron_minThe deviation of (a) satisfies:

|z₁-z_min|≤0.15v_zT (2)

wherein: z is the axial position of the electron, v_zAnd T are each z<z₀Electron axial velocity and cyclotron period of the region; the loaded local electric field applies negative work to the electron beam, and the transverse momentum of the electron beam is reduced, so that the radial oscillation of the electron beam is inhibited.

Further, the absolute value E of the applied radial electric field strength_rThe requirements are as follows:

where ω is z<z₀The electron cyclotron angular frequency of the region suppresses the radial oscillation of the electron beam by optimizing the intensity of the local radial electric field.

The invention has the beneficial effects that:

1. after the electrons pass through the radial electric field region, the transverse momentum and the Larmor cyclotron radius of the electrons are obviously reduced, so that the radial oscillation of the electron beam is obviously inhibited.

2. The method can be applied to the development of low-guiding magnetic field O-type high-power microwave generating devices, and can improve the working efficiency and stability and reliability of the generating devices.

Drawings

FIG. 1 is a schematic view of the method for suppressing radial oscillation of electron beam by applying local electric field according to the present invention

FIG. 2 shows the effect of suppressing radial oscillation of electron beam in the example

Wherein: 1-a cylindrical drift tube; 2-path of movement of electrons

Detailed Description

The method for suppressing the radial oscillation of the electron beam by applying the local electric field according to the present invention will be described in detail with reference to the accompanying drawings and examples.

A schematic diagram of a method for suppressing radial oscillation of an electron beam by applying a local electric field according to the present invention is shown in fig. 1. In a cylindrical drift tube z₀≤z≤z₁In the range, a radial electric field in the-r direction is applied. Under the constraint of a uniform magnetic field, electrons carry out Larmor cyclotron motion, and when passing through a region applying a local electric field, the radial electric field does work on the electrons to change the radial oscillation of the electron beam. When electrons enter the local electric field area and are positioned near the peak value of radial oscillation and leave the local electric field area and are positioned near the valley value of the radial oscillation, the radial electric field along the-r direction can apply negative work to the electrons, so that the transverse momentum of the electron beam is reduced, and the aim of inhibiting the radial oscillation of the electron beam is fulfilled finally.

In the selection of relevant parameters, z₀Axial position z of nearest neighbor electron radial oscillation peak_maxThe deviation of (a) satisfies: | z₀-z_max|≤0.15v_zT，z₁Axial position z closest to the radial oscillation valley of the electron_minThe deviation of (a) satisfies: | z₁-z_min|≤0.15v_zAnd T, the matching of the electron beam and the local electric field can inhibit the radial oscillation of the electron beam. Further optimizing the amplitude of the radial electric field, E_rThe value of (A) satisfies:

the radial oscillation of the electron beam can be more remarkably suppressed.

In the following, an effect of an embodiment of the present invention of applying a local electric field to suppress radial oscillation of an electron beam is shown in fig. 2, where electrons pass through a radius R under the constraint of a uniform axial guidance magnetic field with a magnetic induction B of 0.5T_d25mm cylindrical drift tube. Axial velocity of electronDegree v_z＝2.7×10⁸m/s, transverse velocity v_t＝0.5×10⁸m/s, relativistic factor γ 2.49, the guide center radial displacement R of its motion₀20mm, electron larmor radius of gyration r_L1.42mm, the gyration angle frequency omega is 35.28GHz, and the gyration period T is 0.178 ns. At 0 ═ z₀≤z≤z₁Applying a radial electric field in a range of 128mm, wherein the direction of the electric field is along the-r direction, and the absolute value of the electric field intensity E_r125kV/cm, at this time:

at z₀So that the electron radial oscillation reaches a peak, i.e. z₀Axial position z of nearest neighbor electron radial oscillation peak_maxThe deviation of (2) is 0, the electron motion trajectory is shown in FIG. 2, z₁Axial position z closest to the radial oscillation valley of the electron_minThe deviation of (a) satisfies:

|z₁-z_min|＝0.54mm＜0.15v_zT＝7.21mm

after passing through the radial electric field region, the electron transverse momentum is reduced to 2.27X 10⁶m/s, the Larmor gyration radius is reduced to 0.063mm, and the radial oscillation of the electron beam is obviously inhibited.

Claims (2)

1. A method of suppressing radial oscillations of an electron beam by applying a local electric field, characterized by: the electron beam passes through a radius of R under the constraint of a uniform axial guidance magnetic field with the magnetic induction intensity of B_dThe guide center of the motion of the cylindrical drift tube is radial displacement R₀And has r_L<R₀，R₀+r_L<R_dWherein r is_LElectron larmor radius of gyration; at z₀≤z≤z₁The absolute value of the applied electric field intensity on the electron motion path in the range is E_rThe electric field direction is along the-r direction; radial electric field region start position z₀Axial position z of nearest neighbor electron radial oscillation peak_maxThe deviation of (a) satisfies:

|z₀-z_max|≤0.15v_zT (1)

radial electric field region end position z₁Axial position z closest to the radial oscillation valley of the electron_minThe deviation of (a) satisfies:

|z₁-z_min|≤0.15v_zT (2)

wherein: z is the axial position of the electron, v_zAnd T are each z<z₀Electron axial velocity and cyclotron period of the region; the loaded local electric field applies negative work to the electron beam, and the transverse momentum of the electron beam is reduced, so that the radial oscillation of the electron beam is inhibited.

2. The method of claim 1, wherein applying the local electric field suppresses radial oscillations of the electron beam, and wherein: absolute value E of applied radial electric field strength_rSatisfies the following conditions:

where ω is z<z₀The electron cyclotron angular frequency of the region suppresses the radial oscillation of the electron beam by optimizing the intensity of the local radial electric field.

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