US laser plasma accelerator outputs high-quality high-energy electron beam

US Laser plasma accelerator outputs high-quality high-energy electron beam

Laser plasma accelerators (LAPs) are called "desktop accelerators" because the length of their acceleration cavity can be measured in centimeters instead of kilometers (kilometres). In recent years, due to the rapid development of technology, scientists are expected to develop new and practical laser plasma accelerators. Compared with today's traditional accelerators, laser plasma accelerators are not only very cheap to manufacture, but also have a much smaller impact on land and the environment.

"Body" varies greatly

The research of laser plasma accelerator has been for many years, and has made gratifying progress. In 2004, scientists from the US Department of Energy's Lawrence Berkeley National Laboratory Laser and Optical Accelerator System Comprehensive Research Project showed the electron beam of a laser plasma accelerator with narrow divergent energy for the first time; in 2006, they first increased the electron energy to 1 billion Electronic Volts.

Conventional charged particle (such as electron) accelerators are connected by multiple vacuum metal cavities. The oscillating electromagnetic field applied to the cavity allows the charged particles to be accelerated in the cavity step by step. The main factor that causes charged particles to be accelerated is the magnetic field acceleration gradient , It is expressed in volts per meter. Generally, the higher the energy of the charged particles, the longer the length of the accelerator, so the length of the accelerator can reach several kilometers.

Laser plasma accelerators are different. The laser plasma accelerator developed by scientists of the laser and optical accelerator system comprehensive research project capable of generating 1 billion electron volt electron beams can be placed on the palm of the hand, and its length is only 3.3 cm. When the strong laser focuses the pulse on the free electrons and positive ions in the accelerator, its radiation pressure causes the electrons and ions to separate, resulting in a high-intensity acceleration gradient. Some electrons trailed behind the laser pulse, and some reached near-light speed almost simultaneously. In a short distance, the laser plasma accelerator can maintain an acceleration gradient of hundreds of billions of volts per meter, which cannot be compared with conventional accelerators.

Difficult to measure characteristics

However, the unique electron acceleration method of the laser plasma accelerator and the generation of femtosecond-level electronic pulses have brought difficulties to the measurement technology. People cannot measure the quality of the high-energy electron beams generated by the laser plasma accelerator.

Now, the measurement problem is being gradually solved, thanks to the research team led by Wim Limans, a scientist at the Accelerator and Fusion Research Division of Lawrence Berkeley National Laboratory. Li Mansi is the head of the comprehensive research project of laser and optical accelerator systems. The research team he leads has theorists, computer simulation experts and excellent experimenters who continuously improve the performance of laser plasma accelerators. In the research team, many students have made important contributions to the research and obtained a doctorate. For example, a graduate student in a comprehensive engineering school in France, Gilam Plato, has studied radiation related to X-rays generated by laser plasma accelerators in the project as part of his doctoral thesis. He is currently in California Postdoctoral research at the university.