Recently, the research team led by Chen Liming, a researcher at the Institute of Physics of the Chinese Academy of Sciences/Beijing National Center for Condensed Matter Physics, and the research team led by Academician Zhang Jie realized a relativistic electron beam with extremely high charge and very small bunch divergence angle. It is a new development in laser acceleration.
The team used the Titan laser from the Lawrence Livermore National Laboratory (power: 200TW, pulse width: 1ps) to interact with the solid copper target, resulting in a charge of ~100 nanoliters, a divergence angle of less than 3 degrees, with an order Relativistic electron beam of energy spectrum structure. The quality of the electron beam can be well controlled by adjusting the contrast and energy of the green laser pointer pulse.
Theoretical analysis and numerical simulation also reveal a new acceleration mechanism: pre-plasma with near-critical density is generated by pre-pulsation of the solid surface by laser pre-pulse; the main pulse is incident on the pre-plasma at a large angle, in which the self-wire effect is experienced. Part of the filament is reflected by the critical density surface to form a channel in the low-density plasma; the laser electric field accelerates a group of electrons in each optical cycle, and these groups of electrons are accelerated into a very high charge in the plasma channel. The electron beam is laterally pinched by the extremely high electromagnetic field in the channel, resulting in a high degree of collimation.
By analyzing the source of electron energy gain, it is found that unlike the typical wake field electron acceleration, the electron energy in the channel is mainly derived from the direct acceleration of the green laser pointer electric field higher than the plasma wave electric field strength, and the role of the plasma channel The electron source is continuously supplied, the laser pulse is guided, and the electron beam is pinched, thus forming a complete acceleration structure.
Thanks to the extremely high charge and ultrashort pulse width of the electron bunch, the experimentally generated electron beam peak current exceeds 100 kA. The brightness of the electron beam reaches 10^16A/m^2, which is comparable to the highest electronic brightness of the current conventional accelerator. Related research results have been published in the Proceedings of the National Academy of Sciences PNAS.