双层喷气Z箍缩氖等离子体K层辐射研究

Study on K-shell X-ray production of double-shell neon gas puff Z-pinch

报道了"强光一号"(1.6MA,70ns)加速器驱动双层喷Ne气Z箍缩负载产生K层辐射(光子能量约1keV)的实验研究.喷气负载出口半径为1.5—1.4cm和0.75—0.6cm(半径比2∶1).充气压力相同情况下外层和内层质量比约2.8∶1.在内爆时间约120ns、负载线质量估计值60—70μg/cm时,获得K层辐射产额约7kJ、峰值功率0.28TW,脉冲宽度20ns.X射线分幅图像表明内爆阶段的不稳定性影响较小,最终内爆速度超过25cm/μs,等离子体柱直径至少压缩到2.5mm.随着负载线质量增大、内爆时间增加,K层辐射功率和产额很快下降.对于质量较轻(28—63μg/cm)的负载,时间分辨的K层线辐射谱给出的电子温度达到500eV以上,对较重的负载(72—80μg/cm)则介于300—400eV.K层发射区域的离子密度介于3—9×1019cm-3,参与K层发射的负载质量mK介于17—46μg/cm,其数值与K层产额的大小有正相关性.

The main results of investigation on K-shell X-ray production of double-shell neon gas puff Z-pinch,driven by Qiangguang-I facility （1. 6 MA,70 ns）,are reported. The exit radii of the outer and inner shells are 1. 5—1. 4 cm and 0. 75—0. 6 cm,respectively. Both shells have a throat width of 0. 32 mm,while the ratio of the throat radii is 2. 8∶ 1,to which the mass ratio would be approximately equal for identical plenum pressures. K-shell yield and peak power up to 7 kJ and 0. 28 TW,respectively,for a 20 ns full width at half maximum pulse have been obtained with about 120 ns implosions,the load mass per unit length of which are estimated to be 60—70 μg /cm. Time-resolved X-ray images show that RT instability during the implosion stage has been well suppressed,resulting in a final pinch diameter compressed to less than 2. 5 mm. The final implosion velocity exceeds 25 cm /μs. K-shell yields and peak powers are largely reduced with longer implosion time. For shots with lower mass,i. e. 28—63 μg /cm,the electron temperature inferred from time-gated K-shell spectra should be greater than 500 eV,implying an overheated plasma column being formed in the stagnation stage. While for shots with load mass of 72—80 μg /cm,time resolved electron temperatures are in the range of 300—400 eV. The inferred ion densities of the K-shell emitting region are in the range of （3—9） × 1019 cm-3,which have been used to calculate the mass fractions that contribute to K-shell radiation. Those shots with near 7 kJ yields also have maximum K-shell emitting load mass （about 46 μg /cm）.