Stopping power measurement for low-velocity heavy ions in a high-temperature, high-density plasma target.

实验研究了低能重离子在高温、高电离等离子体靶中的阻止本领。抛射体离子从1.7 MV串列静电加速器输送。靶等离子体是通过用Q开关Nd玻璃激光器照射小的LiH小球产生的。研制了一套用于时间分辨能量损失测量的飞行时间测量系统。我们发现，在等离子体中测得的225 keV/u ^<16>O和180 keV/u ^<28>Si的阻止本领比在冷中性靶中的大3-4倍。为了确定射弹离子的有效电荷，我们测量了^<16>O射弹通过等离子体后的电荷态分布。为此，我们研制了一台具有高传输效率的宽范围磁谱仪。用三个塑料闪烁探测器同时测量了4+、5+和6+电荷态的强度。对于等离子体靶，与冷等效物相比，测量的分布曲线显著地向高电荷态移动。冷物质的最可能电荷态是4+，而等离子体靶的最可能电荷态是5+ - 6+。这个实验结果表明，低原子序数、高度电离的等离子体可以产生比相同密度的冷物质更高的电荷态。这种效应主要归因于可用电子捕获通道数量的减少。因此，我们得出结论，特别是对于低速重离子，有效电荷的增加是负责在等离子体靶的阻止本领的大幅度增强。

We have experimentally investigated the stopping power of low-energy heavy ions in a high temperature, highly ionized plasma target. The projectile ions were delivered from a 1.7 MV tandem electrostatic accelerator. The target plasma was produced by irradiating a small LiH pellet with a Q-switched Nd glass laser. A time-of-flight system was developed for the time-resolved energy loss measurement. We found that the measured stopping power of 225 keV/u ^<16>O and 180 keV/u ^<28>Si in the plasma were larger than these in the cold neutral target by a factor of 3-4. In order to determine the effective charge of the projectile ions we measured the charge state distribution of the ^<16>O projectiles after the passage through the plasma. For this experiment we developed a broad range magnetic spectrograph with high transmission efficiency. The intensity of the charge states 4+, 5+ and 6+ were measured simultaneously by using three plastic scintillation detectors. For the plasma target, compared with the cold equivalent, the measured distribution curve shifted remarkably toward higher charge states. The most probable charge state for the cold matter is 4+, while that for the plasma target is 5+ - 6+. This experimental result shows that a low atomic number, highly ionized plasma can yield higher charge states than cold matter of the same density. This effect is principally attributable to the reduction in the number of available electron capture channels. As a result we conclude that, especially for low-velocity heavy ions, the increase in the effective charge is responsible for the large enhancement of the stopping power in the plasma target.