重离子冷却储存环CSRm双电子复合实验研究类锂36,40Ar15+离子同位素移动

配备电子冷却装置的重离子储存环为开展高电荷态离子的双电子复合（dielectronic recombination，DR）精密谱学研究提供了绝佳的实验平台。本工作在兰州重离子加速器冷却储存环主环（HIRFL-CSRm）上开展了类锂36，40Ar15+离子的双电子复合实验，实验观测了电子-离子质心系能量范围为0~35 eV的双电子复合速率系数谱。通过外推法获得了36，40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2的跃迁能量。同时利用GRASP2K程序理论计算了36，40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2跃迁的质量移动因子和场移动因子，进而得到双电子复合谱的同位素移动值。36，40Ar15+离子2s_1/2→2p_1/2和2s_1/2→2p_3/2同位素移动分别为0.861 meV和0.868 meV。它们均小于目前CSRm上双电子复合实验的实验分辨为~10 meV，进而解释了实验测量的DR谱上未能观察到同位素移动的原因。然而，高电荷态离子的同位素移动场效应与原子序数Z5成正比，因此，在重离子加速器冷却储存环实验环（HIRFL-CSRe）以及未来大型加速器--强流重离子加速器装置（HIAF）上有望通过DR精密谱学方法研究高电荷态重离子甚至放射性离子的同位素移动，进而获得相关原子核的核电荷半径等信息。The cooler storage ring is equipped with an electron-cooler. It is an excellent experimental platform for dielectronic recombination (DR) experiment of highly-charged ions. In this paper, the dielectronic recombination experiments of lithium-like Ar15+ ions with mass number 36 and 40 are conducted at the HIRFL-CSRm(main ring of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou). The experimental electron-ion collision energy scale is from 0 eV to 35 eV. Extrapolation method is exploited to obtain the excitation energies of transitions 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 of the 36,40Ar15+ ions from experimental data. Meanwhile, GRASP2K program is utilized to calculate the mass shift factors and field shift factors of 36,40Ar15+ ions for 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 transitions to obtain isotope shifts in DR spectra. In theoretical calculation, isotope shifts of 36,40Ar15+ ions corresponding to 2s_1/2→2p_1/2 and 2s_1/2→2p_3/2 are 0.861 meV and 0.868 meV, respectively. They are both less than the experimental precision (~10 meV) of these dielectronic recombination experiments at the CSRm, which explains that isotope shifts cannot be distinguished from the experimental dielectronic recombination spectra. However, the field shift of highly-charged ions is proportional to Z5. In the future, the dielectronic recombination experiments of highly-charged heavy ions even radioactive ions will be conducted at the HIRFL-CSRe (experimental ring of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou) and the future large accelerator facility--HIAF(High intensity Heavy-ion Accelerator Facility) to measure isotope shifts to obtain the nuclear charge radius information.     

HIRFL-CSR电子冷却束流位置测量系统

高效率的电子冷却过程,要求电子束与离子束位置平行且重叠。为了同时测量电子束与离子束的位置,在HIRFL-CSR电子冷却装置上研发了以容性圆筒形极板为感应电极的束流位置探测系统。系统测量束流通过探针时产生的脉冲感应信号,并进行傅里叶变换得到频谱信号,分析4个不同电极上频谱信号强度获取束流的位置信息。测量结果表明,该束流位置探测系统测量准确,为定量研究储存环离子累积和电子冷却过程与两种束流相对位置及角度的依赖关系提供了条件。     

EicC束流冷却方案设计与模拟

对核子内部结构的研究是当前理论和实验研究的重要前沿,高能散射实验是探索核子结构的理想工具。中国科学院近代物理研究所计划在已开建的强流重离子加速器项目(HIAF)的基础上,升级建造中国极化电子离子对撞机(EicC)。EicC将提供质心系能量为15～20 GeV的电子和质子双极化束流,对撞亮度设计指标为2×10³³ cm^-2s^-1,离子束的有效冷却是EicC实现亮度目标的关键。针对离子束流初始发射度大、能量高、流强强的特点,EicC采用两级束流冷却方案,首先在增强器(BRing)中利用常规直流电子冷却器降低离子束流发射度,其次在对撞环(pRing)中采用基于能量回收型直线加速器(ERL)的高能束团冷却系统,抑制对撞过程中的离子束发射度增长。以质子束为例,模拟研究了EicC束流冷却装置中电子束的尺寸、温度、冷却段的磁场和束流光学参数对冷却速率和冷却过程的影响,最终得到了满足亮度要求的束流冷却参数。     

HIRFL-CSR重离子束内散射效应

电子冷却本质上是电子冷却作用与重离子束内散射作用的动态平衡过程. 在Bjorken和Mtingwa束内散射理论的基础上, 应用对称椭圆积分的方法做束内散射增长率的数值模拟, 并应用于HIRFL-CSR的磁铁聚焦结构. 计算结果表明, 束内散射不会成为CSR磁聚焦结构设计的障碍, 并且CSR可以达到冷却设计指标.     

兰州重离子加速器冷却储存环中电子冷却性能

为了在兰州重离子加速器冷却储存环(HIRFL-CSR)上开展一维离子束序化的研究,在CSR主环上,对6.39 MeV/u的58Ni19+离子束进行了冷却累积实验。测量了离子束与电子束之间不同的水平、垂直夹角以及不同电子束剖面的情况下,束流累积及束流寿命变化情况;重点研究了离子束衰减过程中动量分散随离子数的变化规律,拟合计算得到了动量分散随离子数按照幂函数衰减的指数;在给定离子数的情况下,动量分散随夹角、电子束剖面的依赖关系,为下一步在CSR上获得纵向一维有序化离子束的研究做准备。在实验中观测到在较大的夹角情况下,离子束出现纵向振荡和中心频率移动。     

利用HIRFL-CSR开展分子离子复合离解研究的可行性分析

介绍了储存环高精度分子谱学研究的科学意义、国内外研究现状和利用HIRFL-CSR开展该项研究的优势,着重论证了HIRFL-CSR分子离子注入实验环的总体设计方案和技术方案。通过在HIRFL-CSR实验环上增建一条分子离子注入线,将实验环改造成能兼顾现有物理实验和大分子物理研究的综合性研究平台,为分子离子复合离解研究提供良好的技术支撑。特别是质量数大于70的分子离子,能显著提高其能量分辨。     

Investigations of the dielectronic recombination of phosphorus-like tin at CSRm

The electron–ion recombination for phosphorus-like~(112) Sn~(35+)has been measured at the main cooler storage ring of the Heavy Ion Research Facility in Lanzhou, China, employing an electron–ion merged-beams technique. The absolute total recombination rate coefficients for electron–ion collision energies from 0 e V–14 e V are presented. Theoretical calculations of recombination rate coefficients were performed using the Flexible Atomic Code to compare with the experimental results. The contributions of dielectronic recombination and trielectronic recombination on the experimental rate coefficients have been identified with the help of the theoretical calculation. The present results show that the trielectronic recombination has a substantial contribution to the measured electron–ion recombination spectrum of~(112)Sn~(35+). Although a reasonable agreement is found between the experimental and theoretical results the precise calculation of the electron–ion recombination rate coefficients for M-shell ions is still challengeable for the current theory.     

Enhancement of electron–ion recombination rates at low energy range in the heavy ion storage ring CSRm

Recombination of Ar¹⁴⁺, Ar¹⁵⁺, Ca¹⁶⁺, and Ni¹⁹⁺ ions with electrons has been investigated at low energy range based on the merged-beam method at the main cooler storage ring CSRm in the Institute of Modern Physics, Lanzhou,China. For each ion, the absolute recombination rate coefficients have been measured with electron–ion collision energies from 0 meV to 1000 meV which include the radiative recombination(RR) and also dielectronic recombination(DR)processes. In order to interpret the measured results, RR cross sections were obtained from a modified version of the semiclassical Bethe and Salpeter formula for hydrogenic ions. DR cross sections were calculated by a relativistic configuration interaction method using the flexible atomic code(FAC) and AUTOSTRUCTURE code in this energy range. The calculated RR + DR rate coefficients show a good agreement with the measured value at the collision energy above 100 meV.However, large discrepancies have been found at low energy range especially below 10 meV, and the experimental results show a strong enhancement relative to the theoretical RR rate coefficients. For the electron–ion collision energy below 1 meV, it was found that the experimentally observed recombination rates are higher than the theoretically predicted and fitted rates by a factor of 1.5 to 3.9. The strong dependence of RR rate coefficient enhancement on the charge state of the ions has been found with the scaling rule of q^3.0, reproducing the low-energy recombination enhancement effects found in other previous experiments.     

放射性次级束流分离器的分离性能北大核心CSCD

放射性次级束流分离器(HFRS)是强流重离子加速器装置(HIAF)上开展放射性次级物理研究的重要装置。HFRS是飞行时间型(PF)碎片分离器,具有大磁刚度、大接受度、大孔径磁铁以及高动量分辨的特点。HFRS采用Bρ-ΔE-Bρ方法纯化弹核碎裂或裂变反应产生的放射性核素,是开展高精度储存环内实验及环外实验研究的重要工具。主要介绍HFRS分离纯化奇异核的能力,采用MOCADI程序模拟单降能器与双降能器下典型弹核碎裂反应和裂变反应中粒子的鉴别和纯化。模拟结果表明:HFRS具有很好的消色散和聚焦特性,对于弹核碎裂反应中轻核的分离采用单降能器系统即可得到很好的纯化效果;而弹核碎裂反应中重核的分离则需采用双降能器系统才可得到很好的纯化效果;对于裂变反应,由于裂变反应的能散较大,则在采用双降能器系统时也仅仅能得到一定的纯化效果。