MRI: Development of an Advanced Cryogenic Gas Stopper for Energetic Rare Isotope Beams

MRI：开发用于高能稀有同位素束的先进低温气体塞

• 批准号: 1428914
• 负责人: Georg Bollen
• 金额: $ 63.39万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1428914&HistoricalAwards=false
• 关键词: MRI; Development; Advanced; Cryogenic; Gas

All of the matter on Earth is composed primarily of stable or long-lived isotopes created in a stellar explosion billions of years ago. However, the isotopes we observe here on Earth comprise only a small fraction of those that are known to exist. Study of short-lived, or rare, isotopes is key to understanding the origin of matter in the universe, how neutrons and protons collectively form into atomic nuclei, and to explore fundamental symmetries of nature. As these rare isotopes are not naturally occurring on Earth, they must be created in powerful particle accelerators, such those at the National Superconducting Cyclotron Laboratory (NSCL), located on the campus of Michigan State University (MSU). There beams of rare isotopes are created at half the speed of light. However, some of the most precise experimental techniques for probing the properties of rare isotopes require beams with energies up to a billion times less than what they are created with at NSCL. These high-energy beams can be slowed using solid degraders and brought to rest in a chamber filled with a buffer gas, a technique currently in use at the NSCL. The development of a next-generation Advanced Cryogenic Gas Stopper (ACGS) will improve the efficiency and speed at which rare isotopes are delivered to experiments, expanding the reach of several experimental programs to even more exotic isotopes. It will benefit the user community of the NSF-funded NSCL and, through the scientific progress it enables, society at large. The project will follow NSCL and MSU policies for ensuring a diverse scientific workforce. A state-of-the-art development project like ACGS, with close ties to a leading research university that actively encourages and supports a multicultural research body, will create an optimal environment for under-represented and minority students to be trained as scientists.The ACGS is a next-generation high-performance linear gas-stopping device for converting fast rare isotope beams into stopped beams that can be used directly or reaccelerated. The delivery of rare-isotope beams over a wide range of energies is necessary to maximize the number of experimental techniques that can be employed. Beams with energies of 0.01 to 100 keV are used in high-precision experiments with ion traps and lasers, to measure nuclear binding energies (masses), to determine nuclear radii and moments, and to test fundamental symmetries at levels complementing much more expensive high-energy experiments. Precision beams of rare isotopes with energies of 0.1 to 20 MeV/u are used to measure cross sections of key reactions that are critical for understanding nuclear synthesis in the cosmos and for nuclear reaction studies that help determine detailed nuclear properties needed for further advances in nuclear theory. After installation at the NSCL, the ACGS will provide high-purity beams with high efficiency, with short extraction times to provide access to short-lived isotopes, and with a high beam rate capability to enable world-class science, in particular with reaccelerated beams. Fast beams provided by NSCL's Coupled Cyclotron Facility will be slowed down in solid degraders prior to being stopped in helium gas inside the ACGS. The thermalized ions are then guided to an extraction orifice using RF ion transport techniques and a low-energy, so called "stopped" beam is formed. The design is tailored to allow the ACGS to accept incident beam rates exceeding 10^8/s. A novel electrode design, compared to existing linear gas stoppers, will provide an order of magnitude higher beam rate capability and cryogenic operation guarantees delivery of clean rare isotope beams. The use of novel RF-carpet ion-transport techniques will provide extraction times as short as ten milliseconds. The ACGS is best suited for the stopping of medium-to-heavy-mass isotopes that have relatively narrow range straggling distributions in the helium gas and will constitute a high-performance complement to the light-ion Cyclotron Stopper already being built at the NSCL. The availability of intense stopped and reaccelerated beams of short-lived isotopes will play a critical role in the future research program at the NSCL and will be a key feature of research at the Facility for Rare Isotope Beams (FRIB) under construction at MSU.

地球上的所有物质主要由数十亿年前恒星爆炸产生的稳定或长寿的同位素组成。 然而，我们在地球上观察到的同位素只占已知存在的同位素的一小部分。 对短寿命或稀有同位素的研究是理解宇宙中物质起源、中子和质子如何共同形成原子核以及探索自然界基本对称性的关键。 由于这些稀有同位素不是在地球上自然产生的，它们必须在强大的粒子加速器中产生，例如位于密歇根州立大学（MSU）校园内的国家超导回旋加速器实验室（NSCL）。 在那里，稀有同位素的光束以光速的一半速度产生。 然而，一些用于探测稀有同位素性质的最精确的实验技术需要能量比NSCL所产生的能量低10亿倍的光束。 这些高能光束可以使用固体降能器减慢，并在充满缓冲气体的腔室中静止，这是NSCL目前使用的技术。 下一代先进低温气体塞（ACGS）的开发将提高稀有同位素交付实验的效率和速度，将几个实验计划的范围扩大到更奇异的同位素。 它将使NSF资助的NSCL的用户社区受益，并通过它实现的科学进步，使整个社会受益。该项目将遵循NSCL和MSU的政策，以确保多样化的科学劳动力。像ACGS这样的最先进的发展项目与一所积极鼓励和支持多元文化研究机构的领先研究型大学有着密切的联系，将为代表性不足和少数民族学生培养成为科学家创造最佳环境。ACGS是下一代高性能线性气体停止设备，用于将快速稀有同位素束转换为可以直接使用或再加速的停止束。 在很宽的能量范围内提供稀有同位素束是必要的，以最大限度地增加可以采用的实验技术的数量。 能量为0.01至100 keV的电子束用于离子阱和激光的高精度实验，测量核结合能（质量），确定核半径和矩，并在补充更昂贵的高能实验的水平上测试基本对称性。能量为0.1至20 MeV/u的稀有同位素的精确束流用于测量关键反应的横截面，这些反应对于理解宇宙中的核合成和核反应研究至关重要，有助于确定进一步推进核理论所需的详细核性质。 安装在NSCL后，ACGS将提供高效率的高纯度光束，具有短提取时间以提供短寿命同位素，并具有高光束速率能力，以实现世界级的科学，特别是再加速光束。由NSCL的耦合回旋加速器设施提供的快速光束将在ACGS内的氦气中停止之前在固体降能器中减速。然后使用RF离子传输技术将热化离子引导到提取孔，并且形成低能量的所谓“停止”束。该设计经过调整，允许ACGS接受超过10^8/s的入射光束速率。与现有的线性气体塞相比，一种新型的电极设计将提供一个数量级的更高的射束速率能力，并且低温操作保证了清洁的稀有同位素射束的输送。使用新的RF地毯离子传输技术将提供短至10毫秒的提取时间。ACGS最适合于停止中到重质量同位素，这些同位素在氦气中具有相对较窄的范围离散分布，并将构成对已经在NSCL建造的轻离子回旋加速器停止器的高性能补充。短寿命同位素的强烈停止和再加速束的可用性将在NSCL未来的研究计划中发挥关键作用，并将成为MSU正在建设的稀有同位素束设施（FRIB）研究的关键特征。