电离毛细管等离子体在激光加速领域的应用

Laser acceleration is a new type of acceleration mechanism proposed in recent years. It uses plasma as the acceleration medium so it is strongly affected by the properties of plasma. Laser acceleration can achieve acceleration gradients that are three orders of magnitude higher than those obtained by conventional accelerators, which makes it a strong contender for the construction of future compact high energy particle accelerators and radiation sources. However, high gradient and transient acceleration also lead to low energy conversion efficiency and instability of laser acceleration, which are challenges that must be overcome in this field. On one hand, in the absence of guidance, the focused laser beam will diverge rapidly and maintain high intensity only in a short distance, which greatly limits the energy of the accelerated particles; on the other hand, the laser-accelerated particle beam has the characteristics of wide energy spectrum and large divergence angle. In order to meet the requirements of practical applications, it is necessary to use focusing elements to collect and focus the particle beam. At the same time, in order to demonstrate the advantage of high acceleration gradient of laser accelerators, corresponding compact beam focusing devices must be matched. Tailoring and controlling the properties of plasma is essential for the accurate design, operation and application of laser plasma accelerators. As a reliable tool for stably generating plasma channels and modulating plasma parameters, capillary discharge can provide solutions to these problems above-mentioned. The capillary discharge is often described as a cm-long, gas-filled, elongated chamber with an mm-diameter circular cross section implanted in a sapphire or glass block. The plasma is generated in the capillary by an electrical discharge current between two electrodes at the ends, and the plasma’s parameters, such as the density and temperature, can be easily adjusted by changing the geometric structure of the capillary, the gas pressure, and the current setting. The capillary discharge plasma can not only carry the high-gradient acceleration field of the laser plasma wake, but also provide the high-gradient transverse focusing magnetic field driven by the discharge current, which makes it widely used in the field of laser acceleration. Combining high-gradient acceleration fields with high-gradient transmission fields using plasma technology, compact table-top laser accelerators are expected to be truly realized. This review introduces the working principle and characteristics of capillary discharge plasma, and summarizes its main applications in the field of laser acceleration: As an acceleration section, it can extend the acceleration distance and further improve the energy and quality of laser plasma accelerated particle beams; as a beam transmission element, it can achieve axisymmetric focusing on the scale of centimeters to tens of centimeters to increase the cluster density and improve the practical application level of laser accelerated particle beams. On the basis of summarizing the existing research progress, the future development trend of capillary plasma is prospected, and the construction of the capillary discharge plasma platform of Peking University is briefly introduced.