Particle accelerator and design method thereof

Abstract

The invention discloses a particle accelerator and a design method thereof. The particle accelerator comprises two three-section prisms which are symmetrically arranged up and down; the three-section type prisms are three-stage prisms of which the inclination angles of the outer side surfaces are changed stage by stage, a channel between the two nth-stage prisms is an nth-stage acceleration channel, and n is equal to 1, 2 or 3; the total internal reflection angle between laser and an air interface of the nth-stage acceleration channel after the laser is hit into the nth-stage prism is alpha n, alpha 1 > alpha 2 > alpha 3, the outer surfaces of the prisms are of a stepped cascade structure, particle beams are accelerated and bunched at the same time, and focusing of an external magnet is not needed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of particle accelerators, and particularly relates to a particle accelerator and a design method thereof. BACKGROUND

[0002] Particle accelerators are indispensable tools in scientific research and industrial applications, and are widely used in basic physics research, medical equipment and industrial detection fields. At present, the radio frequency accelerator is the mainstream of the linear accelerator scheme, which generates radio frequency waves through a magnetron or a klystron to form a standing wave or a traveling wave electric field in the waveguide cavity to achieve particle acceleration.

[0003] However, the traditional radio frequency accelerator needs to use a microwave power source and an additional large focusing magnet, so it has a large floor area and high cost. Since the damage threshold of metal is lower than that of dielectric, the acceleration gradient will decrease, and the particle accelerator cannot be miniaturized, which is difficult to meet the demand of future desktop medical accelerators. SUMMARY

[0004] The present application provides a particle accelerator and a design method thereof

[0005] Technical scheme: The present application provides a particle accelerator, comprising two three-section prisms arranged symmetrically up and down; the three-section prisms are three-stage prisms with the inclination angle of the outer side surface changing step by step, the channel between the two nth-stage prisms is the nth-stage acceleration channel, n = 1, 2, 3; the total internal reflection angle of the laser after entering the nth-stage prism and the air interface of the nth-stage acceleration channel is α n , α1> α2> α3.

[0006] Further, α1= 30.59° ± 1°, α2= 29.16° ± 1, α3= 27.87° ± 1.

[0007] Further, the shape of the first-stage prism is a triangle, the shapes of the second-stage and third-stage prisms are trapezoids, the inner side surfaces of the three-stage prisms are common sides, and the lengths of the acceleration channels of each stage are the same.

[0008] Further, the expression of the included angle between the extension line of the outer side surface side of the first-stage prism and the outer side surface of the second-stage prism is as follows:

[0009] wherein, is the included angle between the laser after entering the second-stage prism and the vertical direction of the outer side surface of the second-stage prism;

[0010] The expression of the included angle between the extension line of the outer side surface side of the second-stage prism and the outer side surface of the third-stage prism is as follows:

[0011] ;

[0012] wherein, is the angle between the laser and the vertical direction of the outer surface of the third prism after the laser is incident into the third prism.

[0013] Further, when the laser is incident into the third prism from any point on the outer surface of the third prism, the coordinates of the point reached in the third accelerating channel are wherein z is the horizontal coordinate and x is the vertical coordinate, and satisfy the following conditions:

[0014] ;

[0015] ;

[0016] wherein, is the angle between the laser and the vertical direction of the outer surface of the third prism after the laser is incident into the third prism, is the coordinates of the end point of the outer surface of the second prism.

[0017] Further, the angle between the laser and the vertical direction of the outer surface of the nth prism is and the angle between the laser and the vertical direction of the outer surface of the nth prism after the laser is incident into the nth prism is ;

[0018] ;

[0019] ;

[0020] ;

[0021] ;

[0022] wherein, is the angle between the extension of the outer surface side of the first prism and the outer surface of the second prism, is the angle between the extension of the outer surface side of the second prism and the outer surface of the third prism.

[0023] A parameter design method of a particle accelerator, which designs a three-stage stepped phase curve according to the phase slip of particles, determines the energy growth and slip degree of the particles, and makes the slip curve of each stage approximate, thereby determining the phase velocity and accelerating channel length of each accelerating channel.

[0024] Further, the energy growth condition and the expression of the slip degree of the particle are shown as follows:

[0025] ;

[0026] ;

[0027] dz;

[0028] wherein, is a relativistic Lorentz factor, q is the electronic charge, m0 is the electronic mass, E m is the electric field strength of the accelerating field in the channel, is the transverse wave vector of the accelerating field, is the transverse position of the particle in the accelerating channel, is the initial phase of the particle emission, represents the longitudinal position of the accelerated particle, is the phase velocity of the n-th accelerating channel, is the electron velocity, and ω is the angular frequency of the laser.

[0029] Advantages:

[0030] 1) The medium prism structure adopted in the application improves the damage threshold and thus improves the accelerating gradient.

[0031] 2) The stepped cascade structure of the outer surface of the prism adopted in the application realizes simultaneous acceleration and bunching of the particle beam, and no external magnet focusing is needed.

[0032] 3) The stepped prism structure can be manufactured through deep etching process, which reduces the production difficulty.

[0033] 4) The application is beneficial to reducing the volume of the accelerator so as to realize desktopization.

[0034] 5) The application uses the phase slip method to accelerate the electron, which has a certain range of energy fault tolerance, thus reducing the requirement for the energy dispersion of the particle beam.

[0035] 6) The application does not need phase jump technology, thus improving the consistency of particle acceleration. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a sectional view of the particle accelerator of the application; Figure 2 is a phase design curve diagram; Figure 3Figures of phase velocity of longitudinal electric field and accelerating field in time domain in the center of the accelerating channel obtained by simulation, wherein figure (a) is a figure of longitudinal electric field in time domain in the center of the first accelerating channel, figure (b) is a phase velocity figure of the first accelerating channel; figure (c) is a figure of longitudinal electric field in time domain in the center of the second accelerating channel; figure (d) is a phase velocity figure of the second accelerating channel; figure (e) is a figure of longitudinal electric field in time domain in the center of the third accelerating channel, and figure (f) is a phase velocity figure of the third accelerating channel; Figure 4 Figure of energy spectrum distribution of the particle beam; Figure 5 Figure of x-βx phase space distribution of the particle beam; wherein figure (a) is a figure of x-βx phase space distribution of the particle beam in the front of the first accelerating channel, figure (b) is a figure of x-βx phase space distribution of the particle beam in the center of the first accelerating channel, figure (c) is a figure of x-βx phase space distribution of the particle beam in the front of the second accelerating channel, figure (d) is a figure of x-βx phase space distribution of the particle beam in the center of the second accelerating channel; figure (e) is a figure of x-βx phase space distribution of the particle beam in the front of the third accelerating channel, figure (f) is a figure of x-βx phase space distribution of the particle beam in the center of the third accelerating channel, and figure (g) is a figure of x-βx phase space distribution of the particle beam in the rear of the third accelerating channel; Figure 6 Figure of the passing rate curve of the particle beam. DETAILED DESCRIPTION

[0037] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application, illustrate the preferred embodiments of the application and assist in

[0038] The principle of the present application is to use a 2-micron wavelength ultrafast laser with a half-height power of 160 fs and an amplitude of 1 GV / m to excite a symmetric medium prism to generate an accelerating field in the center of the channel.

[0039] The schematic diagram of the three-stage prism of the present embodiment is shown in Figure 1 The structure has a total length of 100 μm. The three-stage prism is composed of three triangular prisms arranged symmetrically on the upper and lower sides and having gradually changed inclination angles. The first stage is a triangular prism, and the last two stages are trapezoidal prisms. Each stage has an accelerating length of 33.33 microns, and the structure has a total length of 100 μm. When the laser is incident from any point on the outer side of the third-stage prism into the third-stage prism, the coordinates of the point reached in the third-stage accelerating channel are wherein z is the horizontal coordinate, and x is the vertical coordinate, and satisfy formula 1:

[0040]

[0041] ​​ .

[0042] wherein, is the angle between the laser which is shot into the third level prism and the vertical direction, is the coordinate of the end point of the outer surface of the second level prism.

[0043] α1, α2, α3 are the total internal reflection angles of the laser which is shot into the medium and the air interface of the intermediate acceleration channel (α1=30.59°±0.1°, α2=29.16°±0.1°, α3=27.87°±0.1°); the laser is vertically incident to the side surface of the first level prism according to the first level α1, and the deviation angle range is 0.1°; the angle between the laser which is incident to the n level prism and the vertical direction of the outer surface of the n level prism is , and the angle between the laser which is incident to the n level prism and the vertical direction of the outer surface of the n level prism is ; and The expression is as follows:

[0044] ;

[0045] ;

[0046] ;

[0047] .

[0048] wherein, is the angle between the extension line of the outer side surface of the first level prism and the outer side surface of the second level prism, is the angle between the extension line of the outer side surface of the second level prism and the outer side surface of the third level prism, n=1, 2, 3; and are determined by , , The expression is as follows:

[0049] ;

[0050] The angle between the extension line of the outer side surface of the second level prism and the outer side surface of the third level prism The expression is as follows:

[0051] ;

[0052] wherein, is the angle between the laser which is incident to the second level prism and the vertical direction of the outer surface of the second level prism, The angle between the laser beam incident inside the third-order prism and the perpendicular direction of the outer surface of the third-order prism.

[0053] When the laser strikes the outer surface of the prism, the different tilt angles of the sides at each stage of the prism's outer surface lead to inconsistent total internal reflection angles at the incident medium-air interface, causing the acceleration phase velocity within the channel to gradually increase. The expression for the acceleration phase velocity within the channel is shown below:

[0054] ;

[0055] in, At the speed of light, This represents the phase velocity of the acceleration field at the nth stage.

[0056] The three-segment stepped phase curve designed based on the phase slip of the particle (100 keV) is as follows: Figure 2 As shown, when a particle first enters the channel, its phase velocity is lower than the acceleration field's phase velocity. Therefore, it slides from -140° to -220°. Due to acceleration, when the particle's velocity exceeds the acceleration field's phase velocity, it slides in the opposite direction, returning to 140°. This process is repeated periodically at each stage. The particle's energy growth and sliding degree are determined by the following formula, approximating the sliding curve of each stage. This determines the phase velocity of the acceleration field and the length of the acceleration channel at each stage. During acceleration, the particle periodically experiences divergent and focused phases, thus achieving simultaneous acceleration and particle focusing. The acceleration process and the longitudinal electric field in the time domain at the center of the acceleration channel are shown below. Figure 3 As stated above.

[0057] In this embodiment, the incident particle energy is 103.6 keV, the charge is 0.01 fC, and the longitudinal beam length is 0.12 μm. Figure 4 The energy spectrum distribution of particle beam acceleration, Figure 5 This is a phase space distribution diagram of the particle beam x-βx. Figure 6 This is a particle beam throughput diagram; from Figure 4 Figures 5 and 6 show that the particles are accelerated to 144 keV over a distance of 100 μm, with an average acceleration gradient of 400 MV / m, and the particle beam throughput reaches over 90%. The beam-gathering effect in this embodiment is obvious.

[0058] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A particle accelerator, characterized by, The application relates to a laser beam collimator, which comprises two three-section prisms arranged symmetrically upside down; the three-section prisms are three-stage prisms with the outer side angle changing step by step, the passage between two nth-stage prisms is an nth-stage accelerating passage, n=1, 2, 3; the total internal reflection angle of laser beam with the air interface of the nth-stage accelerating passage after the laser beam enters the nth-stage prisms is alpha n , alpha1>alpha2>alpha3.

2. A particle accelerator according to claim 1, wherein α1= 30.59°±1°，α2= 29.16°±1，α3=27.87°±1。 3. A particle accelerator according to claim 1, wherein The first grade prism is triangular, the second and third grade prisms are trapezoidal, the inner sides of the third grade prisms are common sides, and the lengths of the acceleration channels of each grade are the same.

4. A particle accelerator according to claim 1, wherein The angle between the extension of the first-order prism outer side surface edge and the second-order prism outer side surface The expression is as follows: ； wherein, is the angle of incidence of the laser light on the second prism; and is the angle of incidence of the laser light on the second prism; and The angle between the extension of the lateral edge of the second prism and the lateral face of the third prism The expression of the angle is as follows: ； wherein, is the angle of incidence of the laser light on the third prism.

5. A particle accelerator according to claim 1, wherein When the laser is incident to the 3rd prism from any point on the outer side of the 3rd prism The coordinates of the point reached in the 3rd accelerating channel are where z is the transverse coordinate and x is the longitudinal coordinate, and satisfy the following conditions: ; ; wherein, is the angle of the laser light incident into the third prism with the vertical direction of the outer surface of the third prism, is the coordinate of the end point of the outer surface of the second prism.

6. A particle accelerator according to claim 1, wherein The angle between the laser incident to the n-th prism and the vertical direction of the outer surface of the n-th prism is , and the angle between the laser incident to the inner surface of the n-th prism and the vertical direction of the outer surface of the n-th prism is . ; ; ; ； wherein, is an angle between an extension line of the first-order prism outer side surface edge and the second-order prism outer side surface, is an angle between an extension line of the second-order prism outer side surface edge and the third-order prism outer side surface.

7. The method of claim 1, wherein the method is used for designing parameters of a particle accelerator. According to the phase slip of the particles, a three-stage ladder phase curve is designed, the energy growth and slip degree of the particles are determined, the slip curve of each stage is approximated, and the phase velocity and the length of the acceleration channel of each stage are determined.

8. The parametric design method of claim 7, wherein, The expression of the energy growth and slip degree of the particles is as follows: ; ; dz; wherein, is the relativistic Lorentz factor, q is the electron charge, m0is the electron mass, E m is the electric field strength of the accelerating field inside the channel, is the transverse wave vector of the accelerating field, is the transverse position of the particle inside the accelerating channel, is the initial phase of the particle emission, denotes the longitudinal position of the accelerated particle, is the phase velocity of the nth accelerating channel, is the electron velocity, and ω is the laser angular frequency.

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