Energy selection method of laser proton accelerator based on chromatic aberration effect

Abstract

The invention discloses a chromatic aberration energy selection method of a laser acceleration proton beam, which adopts a method of combining a superconducting solenoid, an energy reducer and an energy selection diaphragm to realize the proton beam energy selection function and reduce the volume of a beam transmission line. And finally, obtaining a laser proton beam with energy dispersion less than 6% for treating cancers in a later-stage scattering scheme.

Description

Technical Field

[0001] The invention relates to a laser proton accelerator, and in particular to an energy selection method for a laser proton accelerator based on a chromatic aberration effect and coordinated with a superconducting solenoid, an energy degrader and an energy selection aperture. Background Art

[0002] Traditional photon radiotherapy such as X-rays has serious side effects and poor effects, leading to a high recurrence rate. However, due to the existence of Bragg peaks, protons and heavy ions have great advantages in irradiating the human body. After entering the human body, they will not release a large amount of energy immediately, but only release most of their energy at the location where the ions stop. They can effectively kill deep tumors while minimizing damage to shallow normal tissues. However, ion acceleration equipment based on radio frequency accelerators is large in size, expensive, and has high maintenance and operation costs, making it difficult to popularize.

[0003] The laser-driven proton therapy device is a new type of proton accelerator being designed by Peking University. It is the world's first laser-driven proton accelerator. Protons will be generated by laser-plasma interaction, and a 2PW laser will be used to make the proton energy reach 100MeV. The acceleration gradient of the laser accelerator using the new principle can reach more than 100GV / m (at least 3 orders of magnitude higher than the radio frequency accelerator), which can significantly reduce the size and cost of the accelerator. Ultra-strong and ultra-short laser-driven accelerators have become one of the most attractive topics in the accelerator industry in recent years due to their high acceleration gradients.

[0004] Traditional proton cancer accelerators use synchronized rings to accumulate beams and synchronize acceleration to achieve the dose required for tumor treatment. For laser-driven proton beams, the acceleration distance is less than 10 microns; and laser-driven proton beams have the characteristics of large divergence angle and large energy dispersion. As the transmission distance increases, the beam transmission efficiency will gradually decrease. Summary of the invention

[0005] In order to solve the technical problems existing in the above-mentioned prior art, the present invention proposes an energy selection method combining a superconducting solenoid, an energy degrader and an energy selection aperture, wherein the superconducting solenoid is used to collect the beam, the energy degrader blocks the low-energy beam, and the chromatic aberration effect is used to complete the final energy selection at the energy selection aperture, thereby improving the transmission efficiency of the beam.

[0006] The present invention provides a chromatic aberration energy selection method for laser accelerated proton beam, which is characterized by comprising the following steps:

[0007] S1. Through the first superconducting solenoid, the beam is initially collected and the lateral size of the beam is compressed;

[0008] S2, after passing through the first drift section, the low-energy particles are filtered out through the energy degrader;

[0009] S3, after passing through the second drift node, it enters the second superconducting solenoid for recollection;

[0010] S4. The beam passes through the third drift node and then through the energy selection aperture.

[0011] In some embodiments, the method further includes determining the required central energy by controlling the magnitude of the solenoid magnetic field.

[0012] In some embodiments, the method further includes determining the energy spread of the beam by controlling the radius of the energy selection aperture.

[0013] The method of the present invention abandons the complex transmission system used in traditional cancer treatment accelerators, and adopts a relatively simple chromatic energy selection combination of a solenoid, an energy degrader and an energy selection aperture, and uses a more miniaturized beam transmission line to complete the selection of the target energy required for cancer treatment, and can control the beam transmission energy dispersion to facilitate Bragg peak superposition during the treatment process, ensuring that different depths of the irradiated lesions can receive uniform and controllable dose irradiation; the present invention will use a combination of chromatic energy selection and an energy degrader to complete the transmission and delivery of the laser-driven proton beam, and promote the laser-driven proton therapy device project. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of an embodiment of the laser accelerated proton beam transport system based on the combination of chromatic aberration energy selection and energy degrader of the present invention. DETAILED DESCRIPTION

[0016] In order to solve the technical problems existing in the above-mentioned prior art, the present invention proposes an energy selection method combining a superconducting solenoid, an energy degrader and an energy selection aperture, wherein the superconducting solenoid is used to collect the beam, the energy degrader blocks the low-energy beam, and the chromatic aberration effect is used to complete the final energy selection at the energy selection aperture, thereby improving the transmission efficiency of the beam.

[0017] One object of the present invention is to provide a method for chromatic aberration energy selection of laser accelerated proton beam.

[0018] The laser accelerated proton beam homogenization method of the present invention comprises: a superconducting solenoid S1#, an energy degrader, a superconducting solenoid S2# and an energy selection aperture; the motion state of the beam passing through the superconducting solenoid and the drift section is calculated according to beam dynamics, the parameter changes before and after the beam passes through the energy degrader are calculated by Monte Carlo simulation, and the motion state of the beam after passing through the drift section, the solenoid and the energy selection slit is calculated by beam dynamics subsequently, and finally a laser proton beam with an energy dispersion less than 6% is obtained, which is used for the late scattering scheme to treat cancer.

[0019] The beam chromatic aberration energy selection beamline includes: the first superconducting solenoid, the energy degrader, the second superconducting solenoid and the energy selection aperture. The beam parameters in one direction during the beam transmission process will be expressed in the form of a 2*1 matrix. The z direction is the beam motion direction, and two mutually perpendicular x and y directions are defined on the plane perpendicular to the axis. In the subsequent calculation process, the motion state of the beam is described by 2*1 matrices in three directions respectively, and the force acting on the change of the beam motion state will be described by a 2*2 matrix.

[0020] The motion state of the beam entering the beam chromatic aberration energy selection process can be expressed by the following matrices:

[0021]

[0022] Among them, xyz represents the position of the beam in the three directions of xyz, and x′y′z′ represents the momentum in the three directions of xyz.

[0023] The beam drift section is also called the drift node. When the beam passes through the drift node, it is not affected by external forces and will continue its previous motion state. The transmission matrix is ​​as follows:

[0024]

[0025] Where Δs is the drift node length and γ is the relative velocity of the beam.

[0026] The motion state of the beam after passing through the drift node can be calculated as follows:

[0027]

[0028] The transmission of a quadrupole magnet can be approximated by the following parameters:

[0029]

[0030] in, is the focusing strength of the beam in the x direction. Since the solenoid is symmetrically focused, k x =k y ,Δs=ρΔα is the magnetic rigidity of the particle. In this calculation process, the focusing magnet is equivalent to a thin lens, that is, a lens without thickness. The beam tends to move toward the center of the beam through the solenoid, which is called focusing; the solenoid only provides lateral force to the beam and does not affect the longitudinal motion state of the beam, so the longitudinal transmission matrix is ​​a unit matrix. The motion state of the beam after passing through the solenoid can be calculated as follows:

[0031]

[0032] The energy degrader can block low-energy beams, and the changes in various parameters of the beam after passing through the energy degrader can be calculated through Monte Carlo simulation.

[0033] The energy loss and exit angle of protons in materials mainly depend on the initial energy of protons, the properties of materials (such as atomic number and density), the path length passed through, and the interaction between protons and material atoms. The energy loss is mainly achieved through ionization loss and radiation loss. The ionization loss dE / dx can be calculated by the following formula:

[0034]

[0035] Among them, m e is the electron rest mass; c is the speed of light; z is the charge number of the incident charged particle (proton is 1); e is the electron charge; β is the ratio of the speed of the incident charged particle to the speed of light β = v / c; γ is the Lorentz factor; Z is the atomic number of the target; A is the atomic mass number of the target; T max is the maximum energy that a charged particle can transfer to a free electron; I is the average ionization energy of the target.

[0036] The proton's exit angle is mainly affected by multiple Coulomb scattering, and the multiple scattering angle can be estimated by the following formula:

[0037]

[0038] Among them, θ0 is the root mean square scattering angle; p is the momentum of the proton; z is the charge number of the proton; x is the thickness of the material passed by the particle; X0 is the radiation length of the material, which means the path length of the charged particle in the material where the energy is reduced to 1 / e of the original.

[0039] According to the above formula, we conclude that the energy degrader can effectively block the low-energy beam from passing through without affecting the normal passage of the high-energy beam. We will use the above characteristics and the chromatic aberration effect of different energies to achieve the selection of corresponding energies, and control the aperture of the energy selection aperture to achieve the regulation of the terminal output energy dispersion. The specific operation process of the beam is as follows:

[0040] The beam is initially collected through the first superconducting solenoid, and the beam is compressed in the transverse direction. After passing through the first drift node, the beam passes through the energy degrader to filter low-energy particles. After passing through the second drift node, the beam enters the second superconducting solenoid for recollection. After passing through the third drift node, the beam passes through the energy selection aperture. The beam is collected by the solenoid, and the focal length of beams of different energies is different. The required central energy can be determined by controlling the magnetic field size of the solenoid, and the beam energy dispersion can be controlled by controlling the radius of the energy selection aperture and modifying the size of the energy selection aperture.

[0041] The method of the present invention abandons the complex transmission system used in traditional cancer treatment accelerators, and adopts a relatively simple chromatic energy selection combination of a solenoid, an energy degrader and an energy selection aperture, and uses a more miniaturized beam transmission line to complete the selection of the target energy required for cancer treatment, and can control the beam transmission energy dispersion to facilitate Bragg peak superposition during the treatment process, ensuring that different depths of the irradiated lesions can receive uniform and controllable dose irradiation; the present invention will use a combination of chromatic energy selection and an energy degrader to complete the transmission and delivery of the laser-driven proton beam, and promote the laser-driven proton therapy device project.

[0042] We simulated the collection process of laser-driven proton beams using TraceWin software and studied the envelope of laser-driven proton beams in CS. The equivalent input parameters were defined using the proton parameters obtained by laser acceleration. The particle source was located 340 mm upstream of the first superconducting solenoid, marked as the "entrance" in 1. CLAPA-II can transmit proton beams of 30-200 MeV, but at the current stage of the project, we need to be able to transmit proton beams with a maximum energy of 100 MeV and an energy spread of less than 5%.

[0043] Figure 1 The CS envelope diagram and structure diagram obtained by simulation under given parameters. The energy selection process is realized by using the combination of solenoid and energy selection aperture.

[0044] The collection efficiency (ηT) of the light beam is expressed as the ratio of the number of particles (NT) passing through the energy selection hole to the total number of particles at the beginning (NTtotal). The 1% energy dispersion selection efficiency (η1%) of the light beam is defined as the ratio of the number of particles with energy dispersion less than 1% (N±1%) passing through the energy selection device to the number of transmitted particles (NT).

[0045]

[0046] This scheme utilizes the chromatic aberration effect of the solenoid, and under the premise of energy dispersion of ±1%, ηT=29.7%.

[0047] The collection efficiency (ηT) of the light beam is expressed as the ratio of the number of particles (NT) passing through the energy hole to the total number of particles at the beginning (NTtotal). The 1% energy dispersion selection efficiency (η1%) of the light beam is defined as the ratio of the number of particles with energy dispersion less than 1% (N±1%) passing through the energy selection device to the number of transmitted particles (NT).

[0048] This scheme utilizes the chromatic aberration effect of the solenoid, and under the premise of energy dispersion of ±1%, ηT=29.7%.

[0049] It should be noted that, for the aforementioned product embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present invention is not limited by the described order of actions, because according to the present invention, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention. In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, please refer to the relevant description of other embodiments.

[0050] In the several embodiments provided by the present invention, it should be understood that the disclosed device can be implemented in other ways. For example, the device embodiments described above are only schematic, such as the division of the modules, which is only a logical function division. There may be other division methods in actual implementation, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, and the indirect coupling or communication connection of devices or modules can be electrical or other forms.

[0051] The modules described as separate components may or may not be physically separated, and the components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed on multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0052] In addition, each functional module in each embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of software functional modules.

[0053] The embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the product of the present invention and its core idea. At the same time, for those skilled in the art, according to the product of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A chromatic aberration energy selection method for laser accelerated proton beam, characterized in that: The following steps are involved: S1. Through the first superconducting solenoid, the beam is initially collected and the lateral size of the beam is compressed; S2, after passing through the first drift section, the low-energy particles are filtered out through the energy degrader; S3, after passing through the second drift node, it enters the second superconducting solenoid for recollection; S4. The beam passes through the third drift node and then the energy selection aperture.

2. The chromatic aberration energy selection method for laser accelerated proton beam according to claim 1, characterized in that: The required central energy is determined by controlling the magnitude of the solenoid magnetic field.

3. A chromatic aberration energy selection method for laser accelerated proton beam according to any one of claims 1 to 2, characterized in that: The energy spread of the beam is determined by controlling the radius of the energy selection aperture.

Images