Traveling wave and standing wave acceleration in linear accelerators

Linear accelerator is a device used to accelerate charged particles, with traveling wave and standing wave acceleration being the two main acceleration methods. The following is a detailed description of these two acceleration methods:

Traveling wave acceleration:

Definition: Traveling wave acceleration is achieved through the interaction between radio frequency electromagnetic waves propagating in the form of traveling waves and charged particles. In a traveling wave linear accelerator, radio frequency electromagnetic waves propagate in a straight direction inside the accelerator tube, interact with charged particles, and thus accelerate charged particles.

Features: The advantages of traveling wave linear accelerators are relatively easy debugging, small energy divergence, and large mode spacing. The two ends of its accelerator tube have matching couplers for the input and output of radio frequency electromagnetic waves, and there is no wave reflection in principle. During the acceleration process of traveling waves, electric field waves move in a straight direction inside the pipeline and will not be reflected when they reach the outlet of the pipeline.

Application example: For example, the Hefei Light Source Linear Accelerator is a conventional traveling wave linear accelerator that uses a traditional DC hot cathode electron gun as the electron source. After focusing the beam through a pre buncher and buncher, it enters an equal gradient traveling wave acceleration structure and ultimately increases the beam energy to 800 MeV.

Standing wave acceleration:

Definition: Standing wave acceleration is achieved by utilizing radio frequency electromagnetic waves to interact with charged particles in the accelerating tube in the form of standing waves. Radio frequency electromagnetic waves are input from any point in the middle of the accelerator tube and reflect back and forth at both ends to form standing waves.

Feature: The advantage of standing wave linear accelerators is their high efficiency. Under the same input RF power and beam energy, a standing wave linear accelerator can significantly shorten the length of the accelerator tube. During the acceleration process of standing waves, although electric field waves also move in a straight direction, they will automatically reflect back and combine with the passing electric field waves to form standing waves when they reach the outlet of the pipeline.

Traveling wave acceleration and standing wave acceleration are the two main acceleration methods in linear accelerators, each with its own characteristics and advantages. In practical applications, appropriate acceleration methods can be selected based on specific experimental requirements and conditions.