RU2641658C2 - Method for slow beam output of charged particles - Google Patents

Abstract

FIELD: physics.SUBSTANCE: method is carried out by using gradient dipole fields that have a gradient force impulse. By increasing the magnetic field of the gradient dipole, the beam is deflected to the output system and defocused to increase its radial size in the aperture region of the output device. When the magnetic field is increased, a part of the beam particles that enters the aperture of the output deflector is withdrawn from the accelerator, and the remaining part is focused and reintroduced into the equilibrium orbit. The magnitude of the magnetic field increases until all the particles of the beam are removed from the accelerator.EFFECT: reducing the magnetic field distortions around the screen and decreasing the loss of beam particles in the deflector wall.1 dwg

Description

The invention relates to accelerator technology, in particular to methods for removing particles from ring systems of accelerators and charged particle storage devices.

There are several ways to slowly output beams. The most widely used conclusion was the use of resonant buildup of betatron vibrations of charged particles [1]. The essence of this method is that in one of the transverse phase planes create conditions of strong nonlinear resonance. The particles of the circulating beam at the beginning occupy a stable region of motion of the phase space. Then conditions are created when the particles cross the separatrix of nonlinear resonance and fall into the unstable region of motion, where the amplitude of the oscillations increases rapidly and the particles fall into the aperture of the output device.

Another output method involves the use of a bypass system deflecting the beam from the equilibrium orbit [2]. In this method, a bypass system is formed by the fields of four identical dipole magnets, which first deflects and then returns the beam to an equilibrium orbit. With increasing magnetic induction of the magnetic fields of the dipoles, the magnitude of the deviation increases. As the beam approaches the magnetic screen, a fast shock magnet is turned on, which deflects the beam path into the magnetic screen. After that, the beam does not return to equilibrium orbit, but is removed from the accelerator.

As a prototype, we choose the output method using the bypass system deviation of the beam from the equilibrium orbit [2]. One of the problems that complicates the implementation of this method of beam extraction is the disturbance of the field by the magnetic screen of the beam output device. The creation of screens with small perturbations of pulsed magnetic fields both in space and in time is a difficult task. In this method of beam extraction [2], it is proposed to use a multilayer copper-iron screen. In addition, the thickness of such a screen is comparable with the transverse dimensions of the output beam, which leads to significant losses of the particle particles in the walls of the screen.

The aim of the invention is to reduce the distortion of the magnetic field around the screen and to reduce particle loss in the walls of the output device bypass beam.

The method consists in the fact that, using time-varying magnetic fields, they gradually deviate the trajectory of the particle beam from the equilibrium orbit, and when the trajectory of the beam reaches the aperture of the output device, particles are removed from the accelerator, the beam particles are simultaneously defocused and deflected from the equilibrium orbit by the magnetic field of the first of the input dipole, part of the deflected and defocused beam particles that have reached the aperture of the output device are output from the accelerator, and the defocused particles are those that do not fall into the aperture of the output device are focused by the fields of the second and third magnetic dipoles and deflected back to the axis, and by the fields of the fourth magnetic dipole, particles not extracted from the accelerator are again brought into equilibrium orbit, the magnetic fields of all dipoles are increased until all particles will not be pulled out of the accelerator, the deflection will be focused and defocused by the fields of dipoles with the force momentum gradient G = d (Ft) / dy (where G is the force momentum gradient, F is the force acting on the particle, t is the force action time y is the cross coordinate of the dipole), while for shielding an alternating magnetic field in the output device of its wall is made of thin non-magnetic metal with a wall thickness more than the skin layer, and to reduce the distortion of the magnetic field in the region of the beam particles that do not fall into the aperture of the output device, the walls of devices perform parallel to the lines of force of the magnetic field.

Distinctive features of the claimed method is the following:

The beam particles are simultaneously defocused and deflected from the equilibrium orbit by the increasing magnetic field of the first dipole at the entrance to the bypass system. As a result of the action of defocusing and deflecting forces, the beam, drifting in the space of the drift between the dipoles, increases its size and the magnitude of the deviation from the axis of the system. With weak fields in the dipoles of the bypass system, all particles of the beam return to equilibrium orbit. With increasing fields, the beam deflection increases and part of the particles, reaching the aperture of the output device (deflector), will be removed from the accelerator. The large beam size at the deflector reduces the loss of particles in its walls. The magnetic fields of the second and third dipoles focus the remaining particles and deflect them toward the axis of the system, where they are introduced into the equilibrium orbit by the field of the fourth dipole. The beam is deflected, focused and defocused using dipole fields with a gradient force momentum G = d (Ft) / dy, (where G is the force momentum gradient, F is the force acting on the particle, t is the force action time y is the transverse coordinate of the dipole), in order to shield the variable, the magnetic fields in the output device of its wall are made of thin non-magnetic metal with a wall thickness greater than the skin layer, and to reduce the distortion of the magnetic field in the region of the beam particles that do not fall into the aperture of the output device, the walls of this device run parallel of the magnetic field lines. The small wall thickness of the outlet deflector and the large beam size at the deflector contribute to a significant reduction in the loss of beam particles. Since the lines of force of an alternating magnetic field always envelope the electrically conductive metal, the walls of the deflector parallel to the lines of force will not cause distortion of the magnetic field.

This goal is achieved in that the combination of all the essential features can significantly reduce the magnetic field distortion by the deflector and the loss of beam particles in the deflector with the bypass method of slow extraction of the particle beam from ring accelerators and particle storage devices.

List of illustrations

In FIG. 1 (Appendix) A diagram of the output of a beam of charged particles from ring accelerators and particle storage using the bypass method of beam deflection,

Where:

1 and 4 — gradient dipoles with a focal length ƒ ₁ (1 — the input dipole defocuses the beam and deflects it from the equilibrium orbit; 4 — the output dipole injects particles into the equilibrium orbit).

2 and 3 — dipoles with focal length ƒ ₂ (they focus the beam and deflect it into equilibrium orbit).

5 - output device (deflector).

l is the drift area.

,

,

- размеры огибающей пучка.

,

,

- dimensions of the envelope of the beam.

ζ is the displacement of the elements of the system.

The method works as follows.

The beam is deflected, focused / defocused using gradient dipoles 1, 2, 3, and 4 (Fig. 1). The momentum gradient of the dipole force is equal to:

Where:

F is the force acting on the particle,

t is the time of flight of the particle in the dipole,

q is the particle charge,

y is the transverse coordinate of the dipole.

Gradient dipole 1 at the entrance to the system defocuses and deflects the beam from the equilibrium orbit and brings it closer to the output device 5 (deflector). In this case, the defocusing beam increases its radial size in order to make it significantly larger than the wall thickness of the deflector in order to reduce the loss of particles in the wall.

The combined action of two gradient dipoles 2 and 3 leads to the inverse deflection of the beam to the equilibrium orbit. In this case, the dipoles focus the beam particles that have not reached the aperture of the output device (deflector).

Gradient dipole 4 at the output of the bypass system brings the beam out of the system into equilibrium orbit.

For the bypass output of the beam to the equilibrium orbit, the following conditions are required:

where l is the length of the drift,

ƒ ₁ - the focal lengths of the gradient dipoles 1 and 4,

ƒ ₂ - focal lengths of gradient dipoles 2 and 3,

The magnitude of the focal lengths is determined by the ratio:

Where:

q is the particle charge,

B ₁ - magnetic induction of dipoles 1 and 4,

B ₂ - magnetic induction of dipoles 2 and 3,

P is the momentum of the particles,

tgα ₁ - geometric parameter of dipoles 1 and 4,

tgα ₂ is the geometric parameter of dipoles 2 and 3.

After turning on the power system of the gradient dipoles and increasing their fields, the deflected beam passing through the bypass system will return to equilibrium orbit until the beam reaches the deflector aperture. Part of the particles that have reached the aperture of the deflector will be removed from the accelerator. The remaining part of the beam particles, having passed the bypass system, will again be introduced into equilibrium orbit. The increase in magnetic fields in gradient dipoles continues until all particles of the beam are removed.

The amount of particle loss in the walls of the deflector is determined from the ratio of the size of the envelope of the beam in the region of the deflector and the wall thickness of the deflector. The beam envelope size in the deflector region α _def is equal to:

Where:

- огибающая пучка на входе в байпасную систему,

- the envelope of the beam at the entrance to the bypass system,

- огибающая пучка в области дефлектора,

- the envelope of the beam in the area of the deflector,

l is the length of the drift plot.

размер огибающей пучка у дефлектора много больше, чем размер α_in на входе в байпасную систему,

, что приведет к уменьшению потерь частиц в стенки дефлектора.At

the beam envelope size of the deflector is much larger than the size α _in at the entrance to the bypass system,

, which will lead to a decrease in particle loss in the walls of the deflector.

For a special case, when uniform magnetic fields are formed, the triangular shape of the magnetic poles of the gradient dipoles is used (Fig. 1). For such dipoles, the magnitude of the dipole force gradient G _1.2 and focal lengths ƒ _1.2 are equal to:

G = qB _{1.2 1.2 1.2} ⋅tgα,

where R _1,2 is the cyclic radius of the particle in fields B ₁₂ , tgα _1,2 is the geometric factor of dipoles (Fig. 1).

where q and P are the charge and momentum of the particle.

Here the index “1” refers to 1 and 4 dipoles, the index “2” refers to 2 and 3 dipoles.

To implement this system of slow particle extraction, dipoles with a magnitude of magnetic induction B _1.2 ≤2T are required, which depends on the charge, mass and energy of the particle. The magnetic poles of the dipoles are made of standard electrical steel.

Literature

1. I. B. Issinsky. “Introduction to the Physics of Charged Particle Accelerators”, Part 4, Publishing Department of the Joint Institute for Nuclear Research, Dubna, Moscow Region, 141980

2. A.V. Bondarenko, N.A. Vinokurov. "Beam extraction from a synchrotron through a magnetic shield." Nuclear instit. and Methods in Physics Research, A 603 (2009), pp. 10-12.

Claims (1)

A method for slowly removing a beam of charged particles from a magnetic system of ring accelerators and particle storage devices, namely, using time-varying magnetic fields, they gradually deviate the path of the particle beam from the equilibrium orbit and, when the path of the beam reaches the aperture of the output device, particles are removed from the accelerator, different by the fact that the beam particles are simultaneously defocused and deflected from the equilibrium orbit by the magnetic field of the first input dipole increasing in time, some of the particles are deflected and the defocused beam that reached the aperture of the output device is removed from the accelerator, and the particles of the defocused beam that do not fall into the aperture of the output device are focused by the fields of the second and third magnetic dipoles and deviate back to the axis, and by the fields of the fourth magnetic dipole, the particles not removed from the accelerator again are introduced into equilibrium orbit, the magnetic fields of all dipoles are increased until all particles are removed from the accelerator, the beam is deflected, focused and defocused by fields the force momentum gradient G = d (Ft) / dy (where G is the force momentum gradient, F is the force acting on the particle, t is the force action time y is the transverse coordinate of the dipole), and for shielding the alternating magnetic field in its output device the walls are made of thin non-magnetic metal with a wall thickness greater than the skin layer, and to reduce magnetic field distortions in the region of the beam particles that do not fall into the aperture of the output device, the walls of this device are made parallel to the magnetic field lines.

Images