Cusp confinement of high-beta plasmas produced by a laser pulse from a freely-falling deuterium ice pellet

Preliminary results of the experimental determination of the particle loss aperture sizes of the spindle cusp magnetic bottle for laser‐produced high‐beta deuterium plasmas are presented. The fully ionized dense plasma (with maximum density ${\text{∼10}}^{16}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}$ and ion energy $\text{∼200\hspace{0.17em}}\mathrm{V}$ ) is produced at the null‐field center of the magnetic bottle, from a freely falling isolated deuterium ice pellet by a focused giant laser pulse. In preparation, the free expansion of laser‐produced plasma has been studied experimentally, and the results indicate that the plasmas produced can maintain the fully ionized condition with prescribed plasma parameters until it expands to a certain prescribed volume if the combination of the physical parameters is properly chosen by considering the electron‐ion recombination as one of the important factors. The experimental results of cusp confinement for the plasma thus produced suggest that the loss aperture size of the ring cusp is much smaller than the local ion gyroradius, in sharp contrast with other results thus far reported. Although the determination of the point cusp aperture radius is less complete, the rough estimates show that it is also smaller than the ion gyro‐radius.