Principle of electron linac

 

Electron linear accelerator is a kind of charged particle accelerator. It uses high microwave power to build up longitudinal electric field in traveling wave and standing wave acceleration structure to accelerate electron beam. The resonant accelerators have been widely used in radiation processing, medical treatment and other fields. This paper will elaborate the principle of electron linAC, including its structure, working principle and performance characteristics.

First, the basic structure of electron linear accelerator

 

The basic structure of electron linear accelerator includes electron gun, accelerator tube, focusing coil, microwave power source, pulse modulator and so on. These parts work together to generate, accelerate and focus the electron beam.

 

Electron gun: The electron gun is the starting part of the electron linear accelerator, which is responsible for generating and emitting electron beams. The electron gun works in pulse state, and the beam energy, pulse current intensity, beam diameter and divergence Angle injected into the accelerator tube are designed according to needs. Generally, Pierce type electron gun is used, and lanthanum hexaboride with high electron emission current density at low temperature is used as cathode material.

 

Acceleration tube: The accelerator tube is the core part of the electron linear accelerator, which is composed of two parts: the bunching section and the acceleration section. The main function of the accelerator tube is to accelerate the electron beam so that it can obtain high energy. In the tube, the electron beam is continuously accelerated by the microwave electromagnetic field, and finally emits at a speed close to the speed of light. The acceleration tube adopts constant temperature water cooling measures, so that the temperature change is not more than 1 degree, to ensure the stability of the electron beam operating parameters.

 

Focusing coil: The role of the focusing coil is to ensure the stable transmission of the electron beam in the acceleration tube and prevent the electron beam from diverging. The focusing coil is set according to the beam envelope focusing requirement in the theoretical calculation, and the trajectory of the electron beam is controlled by adjusting the magnetic field intensity.

 

Microwave power source: The microwave power source provides a microwave electromagnetic field to the accelerator tube, which accelerates the electron beam in the accelerator tube. Microwave power sources can use magnetrons or klystrons to accelerate electrons and provide energy as needed.

Pulse modulator: A pulse modulator provides a pulse high voltage to a microwave power source to generate the required microwave electromagnetic field. The pulse modulator generally adopts the hose linear pulse modulator, which is charged by the DC high-voltage power supply to the charging transformer and the capacitor of the pulse forming line. The high power pulse thyratron is a discharge switch. The pulse forming line forms a discharge circuit through the thyratron and the primary winding of the pulse transformer. The high voltage is formed in the primary of the pulse transformer and the high voltage is output in the secondary of the transformer.

 

Second, the working principle of electron linear accelerator

 

The working principle of electron linAC is based on the acceleration of charged particles by electromagnetic fields. When the electron beam is emitted from the electron gun, it enters the accelerator tube. In the tube, the microwave electromagnetic field generated by the microwave power source accelerates the electron beam. Under the action of microwave electromagnetic field, the electron beam continuously obtains energy, and the speed gradually increases. As the electron beams approach the speed of light, they will beam out of the accelerator tube, forming a high-energy electron beam.

 

In medical electron linear accelerators, high-energy electron beams further hit metal targets to produce high-energy X-rays. These high-energy X-rays have the characteristics of high dose rate, short irradiation time, large irradiation field, good dose uniformity and stability, and small penumbra region. They destroy the DNA of tumor cells through ionizing radiation, so that the cells lose the ability to proliferate, so as to achieve the purpose of eliminating or reducing the tumor.

 

Third, the performance and characteristics of electron linear accelerator

 

Electron linear accelerators have many properties and characteristics, which make them widely used in many fields. First of all, the electron linear accelerator has a high energy output, and its electron energy is generally high (greater than 5MeV), and the output power is from a few kW to tens of kW. This allows electron linacs to produce high-energy electron beams and X-rays for a variety of applications.

 

Secondly, the electron linear accelerator has stable operating parameters. Constant temperature water cooling measures and precise focusing coil Settings ensure stable transmission of the electron beam in the accelerator tube, resulting in a stable output.

 

In addition, the electron linear accelerator also has a flexible configuration and a wide range of applications. According to different application requirements, the parameters of electron gun, accelerator tube and microwave power source can be adjusted to meet different irradiation process requirements. This makes the electron linear accelerator has a wide application prospect in radiation processing, medical treatment, scientific research and other fields.

 

Iv. Summary

 

The electron linear accelerator is a resonant accelerator which uses high microwave power to accelerate the electron beam. It generates high-energy electron beams and X-rays by precisely controlling the process of electron beam generation, acceleration and focusing. These high-energy rays have many advantages, such as high dose rate, short irradiation time, good dose uniformity and stability, so that the electron linear accelerator has a wide range of applications in medical treatment, radiation processing and other fields.

 

With the continuous development of science and technology, electronic linear accelerators will be applied in more fields, bringing more convenience and breakthroughs to human life and scientific research. At the same time, we also need to pay attention to the potential risks and challenges it may bring, and ensure its safe, efficient and stable operation through continuous research and innovation.