MRI: Development of a Helium-Jet Ion-Guide System for Harvesting Rare Isotopes and Commensal Operation at NSCL

美国国家超导回旋加速器实验室（National Superconducting Cyclotron Laboratory，简称NSCL）是美国首屈一指的以研究核结构为目的的原子核加速设施。NSCL开发了世界上独一无二的再加速稀有同位素光束的新实验能力，确保在全球稀有同位素物理领域继续发挥领导作用。随着国家科学实验室最近研究能力的扩大，核物理实验中对这些光束的需求从未如此之高。这里提出的仪器，称为氦喷射离子气体系统（HJ-IGS），将允许同时进行两个实验，每个实验使用国家科学实验室不同的探测器系统，这将扩大实验的数量，从而有助于满足对实验的需求，增加我们对原子核的理解。氦喷射离子源过去曾被用于收集同位素，但使用这样一个系统来收集一些最稀有的同位素的想法是新颖的，研究人员可以在弹丸破碎设施中获得这些同位素。在初级稀有同位素光束的净化过程中，从中央光束路径弯曲的稀有同位素被停止并收集在一个充满氦气的高压电池中，这些电池被气溶胶饱和，停止的同位素将附着在这些气溶胶上。在高压差压下，收集到的同位素迅速通过40米长的毛细管输送到离子源，经过净化后，离子源将同位素注入到一个束流线中，该束流线可以为初级实验中未使用的几个站点中的一个提供电力。这允许同时进行两项实验：一项实验使用弹丸破碎直接产生的快速稀有同位素束，另一项实验使用HJ-IGS中收集的、运输的、电离的和纯化的同位素进行停止或再加速束。在核结构和核天体物理学，以及基本的相互作用和对称性等领域有很高需求的最先进的实验，包括各种各样的技术，如原子陷阱的高精度质量测量，束内激光光谱和偏振，核衰变光谱，以及具有主动目标时间投影室的低能反应研究。

The National Superconducting Cyclotron Laboratory (NSCL) is the nation's premier facility to accelerate nuclei with the purpose of studying nuclear structure. NSCL has developed world-unique new experimental capabilities with reaccelerated rare-isotope beams, ensuring a continued leadership role in rare-isotope physics worldwide. With the recent expansion of research capabilities at NSCL, demand for these beams to be used in nuclear physics experiments has never been higher. The instrument proposed here, called a Helium-Jet Ion Gas System (HJ-IGS) will allow for commensal running of two experiments simultaneously, each using different detector systems at NSCL, which will expand the number of experiments and hence help to meet the demand for experiments that increase our understanding of nuclei.Helium-Jet Ion Sources have been used for harvesting isotopes in the past, but the idea to use such a system to harvest some of the rarest isotopes available to researchers in a projectile fragmentation facility is novel. Rare isotopes that are bent out of the central beam path during the purification process of the primary rare-isotope beam are stopped and collected in a high-pressure cell filled with Helium saturated with aerosols to which the stopped isotopes will attach. With a high-pressure differential, the collected isotopes are quickly transported through a 40 meter-long capillary to an ion source that injects the isotopes, after purification, into a beam line that can feed one of several stations not used in the primary experiment. This allows two experiments to be performed at the same time: an experiment using a fast rare isotope beam directly produced in projectile fragmentation and an experiment with stopped or reaccelerated beams using the harvested, transported, ionized and purified isotopes in the HJ-IGS. State-of-the-art experiments that are in high demand in the fields of nuclear structure and nuclear astrophysics, as well as fundamental interactions and symmetries, and include such diverse techniques as high-precision mass measurements in atom traps, in-beam laser spectroscopy and polarization, nuclear decay spectroscopy, and low-energy reaction studies with an active-target time projection chamber.