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arXiv 1905.09459physics.ins-detphysics.app-ph
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下一代反几何散裂驱动超冷中子源

A next-generation inverse-geometry spallation-driven ultracold neutron source

K. K. H. Leung, G. Muhrer, T. Hügle, T. M. Ito, E. M. Lutz, M. Makela, C. L. Morris, R. W. Pattie,, A. Saunders, A. R. Young

摘要:

提出了下一代散裂驱动强流超冷中子源的物理模型,该源的超冷中子提取率比现有最强源高出约一个数量级,比现有源高出约三个数量级。这种UCN电流优化源将大大改善目前统计上有限的尖端UCN测量。一种新颖的“逆几何”设计与40 L超流$^4$ He(He-II)一起使用,其用作冷中子(CN)到UCN的转换器,用最先进的过冷低温技术冷却到$\sim$ 1.6 K。我们的设计针对He-II及其容器上的100 W最大热负荷约束进行了优化。在我们的几何结构中,溅射靶对称地缠绕在UCN转换器周围,以允许在相对大体积的钨溅射靶上光栅扫描质子束,从而降低对冷却要求的需求,这使得合理地假设仅水边缘冷却就足够了。我们的设计经过几个步骤的改进,在我们的另一个限制1兆瓦的最大可用质子束功率下达到$P_{UCN}=2.1\times10^9\,/$。然后,我们研究了氦-II散射内核的影响,以及由于加压达到$P_{UCN}=1.8\times10^9\,/$ s的$P_{UCN}$的减少。最后,我们提供了一个设计的UCN提取系统,考虑到所需的He-II热传输性能和实施的He-II遏制箔,允许UCN传输。我们估计一个总的有用UCN电流从我们的源$R_{use}=5\times10^8\,/$ s从一个18厘米直径的指南5米的来源。在保守的“不返回”近似下,该速率可以在具有$^{58}$ Ni(335 neV)截止电势的$<$ 1000 μ L外部实验体积中产生$>1\times10^4\,/$ cm $^3$的提取密度。

英文摘要:

The physics model of a next-generation spallation-driven high-current ultracold neutron (UCN) source capable of delivering an extracted UCN rate of around an-order-of-magnitude higher than the strongest proposed sources, and around three-orders-of-magnitude higher than existing sources, is presented. This UCN-current-optimized source would dramatically improve cutting-edge UCN measurements that are currently statistically limited. A novel "Inverse Geometry" design is used with 40 L of superfluid $^4$He (He-II), which acts as a converter of cold neutrons (CNs) to UCNs, cooled with state-of-the-art sub-cooled cryogenic technology to $\sim$1.6 K. Our design is optimized for a 100 W maximum heat load constraint on the He-II and its vessel. In our geometry, the spallation target is wrapped symmetrically around the UCN converter to permit raster scanning the proton beam over a relatively large volume of tungsten spallation target to reduce the demand on the cooling requirements, which makes it reasonable to assume that water edge-cooling only is sufficient. Our design is refined in several steps to reach $P_{UCN}=2.1\times10^9\,/$s under our other restriction of 1 MW maximum available proton beam power. We then study effects of the He-II scattering kernel as well as reductions in $P_{UCN}$ due to pressurization to reach $P_{UCN}=1.8\times10^9\,/$s. Finally, we provide a design for the UCN extraction system that takes into account the required He-II heat transport properties and implementation of a He-II containment foil that allows UCN transmission. We estimate a total useful UCN current from our source of $R_{use}=5\times10^8\,/$s from a 18 cm diameter guide 5 m from the source. Under a conservative "no return" approximation, this rate can produce an extracted density of $>1\times10^4\,/$cm$^3$ in $<$1000~L external experimental volumes with a $^{58}$Ni (335 neV) cut-off potential.

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