Open magnetic trap with a helically symmetric multiple-mirror plugging

Magnetic mirrors for plasma confinement are being considered as a possible way for fusion again. One of the central questions in mirror research is how to suppress particle and energy losses along the magnetic field lines. There are several possible solutions of this problem. Here, we discuss one specific approach to multiple-mirror confinement. The multiple-mirror confinement reduces axial losses due to the momentum transfer between the periodic magnetic field and the trapped ions. Moving multiple mirrors improve the confinement; this configuration can be achieved by the plasma rotation in the helically corrugated magnetic field. The concept of the helical mirror has been experimentally validated in a laboratory-scale experiment SMOLA at the Budker INP. Direct evidence of the helical confinement has been obtained, with the plasma density in the confinement region increasing more than threefold under optimal experimental conditions compared to the solenoidal magnetic configuration. Remarkably, enhanced confinement persists even at low densities where the ion mean free path relative to binary collisions exceeds the device length, and the multiple-mirror confinement is possible only in case of anomalous scattering. In this talk, we summarize the experimental findings and discuss the possibility to bridge the gap between the laboratory-scale device and fusion-grade ones.