近Bohr速度O^(4+)离子穿过H_(2)后的电荷态分布

Charge State Distribution for O^(4+)Ions with Energy near Bohr Velocity Passing Through H_(2)

基于两体碰撞近似的BEA模型和电子俘获的OBK模型,利用蒙特卡罗的方法计算了0.1~10倍玻尔速度的O^(4+)离子穿过长度为20 cm的H2气体靶后的电荷态分布情况。分析结果表明:5×1014 cm^(-3)是出射离子电荷态升高的临界密度,在此之前,电荷态的变化主要是降低;在此之后,还出现了升高的电荷态。随着靶密度的增加,升高电荷态的比例增大。同一靶密度下,平均出射电荷态随入射离子速度的增大而增加。10 v0的O^(4+)离子穿过5×10^(18)cm^(-3)的靶后全裸离子的比例可达93%。这为提高加速器出射离子的电荷态提供了重要的理论参考。

Based on the model of BEA for direct coulomb ionization and OBK for electron capture,the distribution of charge state for 0.1~10 v0 O^(4+)ions passing through gaseous target of H2 with length of 20 cm was simulated using the method of Monte Carlo Code.The result indicates that the critical density of charge state increase is about 5×10^(14)cm^(-3).For na<5×10^(14)cm^(-3),the inner-shell process is dominated by electron capture,and the performance of charge-changing is mainly the elevation of the charge state.When na>5×10^(14)cm^(-3),ionization cross section is larger than that of capture,the charge-changing is mainly dwindled.The proportion of elevated charge state is increased with the increase of target density and incident ion velocity.The proportion of bare ions can reach 98%for 10 v0 O4+passing through target with density of 5×10^(18)cm^(-3).This provides an important reference for improving the charge state of ions from accelerator.