SU1764192A1 - Removal device for betatron accelerated electron beam - Google Patents

Abstract

Use: relates to accelerator technology and can be used in the development of betatrons with an extracted electron beam. SUMMARY OF THE INVENTION: The device comprises a capacitor comprising plates 1-3, electromagnet poles, a bias winding 4, a current pulse generator 5 and a voltage pulse generator 6. The acceleration chamber 7 has a conductive coating 8 and is equipped with an injector 9. Plates 1 and 2 are electrically connected to the coating 8 and are located symmetrically with respect to the median plane with a gap for the passage of the beam. The poles are provided with ridges 10, while the input of the capacitor is located in one of the gaps between the ridges of the poles. Injector 9 is installed in the azimuthal space between the ridges of one pole above or below the median plane. 2 Il. CO S XI a and J4) yu

Description

This invention relates to an accelerator technique and can be used in the development of betatrons with an extracted electron beam.

Nowadays, 2 types of devices for outputting an accelerated electron beam from the betatron 1 have been fairly well developed and used. The first method is based on the electromagnetic method of asymmetric displacement of electrons using a sector winding 180 ° long. The sector winding consists of two semi-windings, connected in series and located in the gaps between the chamber and the poles, and connected to a current pulse generator. When a current pulse is passed through the sector winding, the betatron magnetic field inside its location region weakens and changes the frequency of the betatron oscillations of the particles. At a certain value of the average decay rate of the betatron field, a parametric resonance occurs, leading to a sharp increase in the amplitudes of the radial oscillations of the electrons and the beam from the field of action of the focusing forces of the betatron field. The advantages of such a beam extraction device are in its structural simplicity of execution and its simplicity of tuning it to the maximum current of the extracted beam. However, it has significant drawbacks: low efficiency (30%) output and high beam divergence at the exit of the acceleration chamber.

The second type of output device is based on the electrostatic method of deflecting accelerated electrons. It contains an electrostatic capacitor located inside the orbit of release and similar to the first type sector winding for pre-buildup of the amplitudes of the radial oscillations of electrons and supplying them to the region of the capacitor. This device, compared with the first, allows doubling the efficiency of output 1 and obtaining a smaller beam divergence.

The closest technical solution is an electron beam output device from the betatron, combined with injector 2. It contains a vacuum accelerator chamber with an electronic injector, injection voltage and output current pulse generators, a biasable winding and two capacitor plates (in terms of 2 - deflector plates) . The deflector plate deflecting (being under a positive potential) is fixed on the focusing

the injector electrode and is connected to the pulse generator of the injection and output voltage. Such a combination of injection and electron extraction in one device makes it possible to simplify the design of the acceleration chamber and to partially eliminate the loss of electrons on the injector during the extraction process. However, the combined injection and output device did not eliminate the main significant drawback of the electron output using a capacitor (deflector) - the inevitability of electron losses in the output process on a grounded plate and the need for careful adjustment of the position

5 capacitors in the acceleration chamber. In addition, the need to locate the axis of the capacitor along an unwinding spiral increases in the prototype the radial envelope of the injector and thereby worsens

0 conditions for the capture of electrons in acceleration.

The purpose of the invention is to increase the efficiency of electron beam extraction from the betatron.

The goal is achieved by the fact that

5 in an accelerated beam output device comprising an output capacitor, an electron bias winding, output voltage pulse generators and bias current pulses, an accelerator chamber with a conductive coating, the capacitor is made in the form of three plates, two of which are electrically connected to the conductive accelerator coating chambers are located symmetrically with respect to the median plane with a gap equal to or greater than the vertical size of the accelerated electron beam, the input of the capacitor is installed under the crest of the field, and the the ktor is mounted between adjacent ridges of the pole above or

0 under the median plane.

Distinctive features of the prototype of the proposed technical solution are: the introduction of two electrically adjacent electrically with a conductive coating of the accelerator chamber plates arranged symmetrically with respect to the median plane of the interpolar gap; the presence of a gap between the inserted plates equal to or greater than the axial

0 size of the accelerated beam; installation of the capacitor inlet under the pole ridge; placing the injector between the pole ridges above or below the median plane.

All of these distinguishing features in the output devices of the accelerated electron beam from the battalion were not described and were not applied. The introduction of two electrically connected to a conductive coating plate with a gap equal to or greater

The axial size of the output beam is a fundamentally new proposal for an output device that allows you to eliminate losses of the output electrons on a grounded plate, which, combined with the symmetrical winding of expanding the electron orbit and placing the injector outside the median plane, will significantly increase the efficiency of electron extraction. A distinctive feature concerning the installation of the input of the capacitor under the crest of the pole, in the prototype and analogues could not be implemented, since they used azimuthally uniform poles.

It is known from the literature that the injection device is positioned above and below the equilibrium orbit, but unlike the proposed solution, it has a different purpose: increasing the efficiency of the injection process and involves placing the injectors along the entire boundary of the accelerator chamber aperture.

The execution of the output device of the accelerated electron beam from the betatron with the proposed distinctive features has not yet been carried out, therefore, the proposed solution, according to the authors, meets the criterion of significant differences.

Figure 1 shows the scheme of the output device of the accelerated electron beam from the betatron; Figure 2 shows the distribution of the equipotentials of the electric field formed by the capacitor plates and the conductive coating of the accelerating chamber. The floor picture is obtained on an electrolytic bath.

The output device comprises (Fig. 1) a capacitor comprising plates 1-3, a winding 4 of a symmetric displacement of accelerated electrons; a current pulse generator 5 for supplying winding 4; voltage pulse generator b connected to plate 3; an acceleration chamber 7 with a conductive coating 8 and an injector 9 located between the ridges of the pole 10. Plates 1 and 2 are electrically connected to the conductive coating 8. Figure 1 also shows the trajectory 11 of the electron output from the acceleration chamber 7 and the following symbols are entered: r0 - radius of the equilibrium orbit; A - the gap between the plates 1-3; 12 - the median plane of the interpolar space; Gosv - the radius of the orbit of the release of electrons.

The intensity of the electrostatic field formed by the plates 1-3 and the conductive coating 8 is indicated in figure 2 by the vector E.

The plates 1-3 of the capacitor have a radial bend, defined by the path 11 of the output of accelerated electrons.

The proposed device works as follows.

After the electrons have gained maximum energy, the potential plate 3 from the generator b is given a pulse of positive polarity with a flat top, the duration of which is chosen to be longer than the time for electrons to escape from the chamber. At the point in time when the required electrostatic field E is formed in the capacitor (in the initial part of the flat top of the voltage pulse applied to the plate 3), a positive pulse magnetic current is applied to the winding 4 of the symmetric bias. the field coinciding in direction inside the winding 4 with the betatron magnetic field formed by the poles 1. As a result of an increase in the magnetic flux inside the winding 4, the betatron with A 2: 1 ratio in the equilibrium orbit r0 and the electrons begin to move along an unwinding spiral with a certain step h. At the point in time when the current amplitude in the winding 4 approaches its maximum value, the electrons reach the orbit where the capacitor plates 1 and 2 are located.

Due to the fact that the positive potential of plate 3 sags through the gap formed by plates 1 and 2, inside chamber 7 (Fig. 2), electrons, when approaching plates 1 and 2, fall into a local, relatively weak electrostatic field, the intensity vector E which is directed to the equilibrium orbit r0. As a result of the interaction of electrons moving along an unwinding spiral, with this field some buildup of amplitudes of radial oscillations of electrons is possible, which increases the step h and contributes to a more rapid electron capture by the capacitor. Once in the internal electrostatic field of the capacitor to the electrons, besides the Lorentz RL force, lvBz (r) and

/ 2

The centrifugal RC starts to noticeably act the force of the electrostatic field Fi IE, where I, V is the charge and velocity of the electron; Bz is the intensity of the betatron magnetic field; g - current radius.

In order for the electrons to be brought out of the orbit of the release of OSV, and then out of the acceleration chamber along the trajectory of output 11, it is necessary to ensure the equality FE I Pl I – I Rc throughout the azimuthal length of the capacitor. Since the step of the unfolding electron orbit is hA, before the moment of capture of electrons by the field of the capacitor, they can repeatedly cross without loss the gap between the plates 1 and 2, equal to or greater than the vertical size of the beam. Having passed the lossless region of the capacitor, the electrons enter the edge field of the betatron beyond the orbit of release of the state and are removed from the acceleration chamber along the trajectory 11.

Setting the capacitor inlet under the ridge increases the radial pitch of the unfolding of the trajectory of the output 11, since the process of electrons deflecting the capacitor occurs in a magnetic field with decreasing value of the magnetic induction Bz in the course of the electron's movement. An increase in the radial pitch of the trajectory unfolding in turn allows for a shorter azimuthal interval to bring electrons out of the Gosv release orbit and thereby reduce the length of the capacitor and, accordingly, the loss of electrons on its plates 1-3, i.e. improve output efficiency. For example, in the four-row design of the poles of the betatron shown in Fig. 1, calculations of the process of electrons beyond the orbit take an azimuthal length of 45 ° and allow electrons to be transferred beyond the orbit of gov in the magnetic field with a minimum strength Bz .

In the proposed device, the injector 9 is located between the ridges of the poles 10 in the region of the boundary of the action of the focusing

the forces of the betatron field in the axial direction and, therefore, in the process of outputting the accelerated beam in the median plane 12, there are no particle losses on the injector 9.

Claims (1)

Thus, in the proposed device, all elements are excluded, on which the loss of electrons is possible in the process of electrons withdrawal from the accelerating chamber, and when performing these distinctive features, the device allows to bring the output efficiency up to 100%. In addition, the presence of a gap between the plates 1 and 2 in combination with the symmetric displacement of electrons by the winding 4 reduces the requirements for the accuracy of the location of the capacitor in the acceleration chamber, which allows it to be made in the original version. The invention of the accelerated beam output device electrons from the betatron containing an output capacitor, electromagnet poles, an electron bias winding, output voltage pulse generators and bias current pulses, an acceleration chamber with a conductive coating and an injector, due to the fact that, in order to increase the efficiency of the output, the output capacitor is made in the form of three plates, two of which are electrically connected to the conductive coating of the accelerating chamber and are arranged symmetrically with respect to the median plane electron beam, the poles are provided with ridges, while the input The capacitor is located in one of the gaps between the crests of opposite poles, and the injector is installed in the azimuthal distance between the crests of one pole above or below the median plane. "H