Alternating Layer Energy Degrader for Proton Beam Emittance Control
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Solution Overview
Problem
Conventional energy degraders in proton therapy systems cause significant emittance growth and reduced beam transmission efficiency due to particle scattering, limiting the quality and quantity of the final treatment beam.
Innovation Solution
An energy degrader comprising alternating layers of low-Z and high-Z materials or carbon nanotubes oriented in the incident direction of the particle beam, which preferentially scatter particles towards the beam axis, minimizing emittance growth and enhancing forward scattering to improve beam transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional energy degrader made of low-Z material (e.g., graphite) is used to attenuate proton beam energy, then the beam energy can be reduced to the desired level, but significant emittance growth occurs due to particle scattering
Solution Approach 1:
The energy degrader is segmented into multiple alternating layers of low-Z and high-Z materials. Each layer has a thickness of approximately 0.1 to 1.0 mm, creating a laminated structure that processes the beam in stages rather than as a single block, thereby controlling scattering effects
Solution Approach 2:
The energy degrader uses composite material structure combining low-Z materials (graphite, aluminum, lithium) and high-Z materials (tungsten, lead, tantalum) in alternating layers. This composite approach leverages the low scattering of low-Z materials and the high density of high-Z materials to achieve energy attenuation with minimal emittance growth
2Use of energy by moving object
If the energy degrader attenuates the beam to a low level (e.g., 1%), then the desired energy selection is achieved, but beam transmission efficiency becomes very low due to emittance growth and subsequent collimation losses
Solution Approach 1:
The beam attenuation process is divided into multiple small interaction stages through alternating layers, each contributing a small amount of energy loss while maintaining beam quality, rather than requiring a single thick degrader that would cause catastrophic emittance growth
Solution Approach 2:
The invention changes the physical parameters of the degrader structure - using alternating Z-values and optimizing layer thicknesses (0.1-1.0 mm each) to transform the scattering dynamics from a single large interaction to multiple small interactions, improving transmission efficiency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces emittance growth, leading to improved beam transmission efficiency and quality, allowing a higher fraction of the initial beam to be transported for downstream radiation use without significant energy range shifting.
Implementation Method 1
the low-Z material serves to attenuate energy of the beam particles by virtue of scattering
Implementation Method 2
the high-Z material serves to suppress the emittance increase by scattering back the beam particles toward the beam axis
Implementation Method 3
The carbon nanotubes may serve to preferentially scatter beam particles towards the central beam axis as well as attenuate energy thereof
Data Source
AI summary
An energy degrading device for attenuating energy of a particle beam with reduced emittance growth. An energy degrader comprises an emittance control material that can preferentially scatter the beam particles that is incident on a surface with a shallow angle. In one approach, the energy degrader may include alternating layers of a low-Z and a high-Z material, wherein the low Z material serves to attenuate energy of the beam particles by virtue of scattering and the high Z material serves to suppress the emittance increase by scattering back the beam particles toward the beam axis. In another approach, the energy degrader may be composed of carbon nanotubes or a material with oriented crystalline structure that is substantially orientated in the incident direction of the particle beam. The carbon nanotubes may serve to preferentially scatter beam particles towards the central beam axis as well as attenuate energy thereof.