Determination of Transverse Distributions of Ion Plasmas Confined in a Linear Paul Trap by Imaging Diagnostics
Determination of Transverse Distributions of Ion Plasmas Confined in a Linear Paul Trap by Imaging Diagnostics
复制标题
DOI：
10.1143/jjap.47.8017
复制
发表时间：
2008-10
影响因子：
1.5
通讯作者：
K. Ito;K. Nakayama;Shunsuke Ohtsubo;H. Higaki;H. Okamoto
中科院分区：
文献类型：
--
作者：
K. Ito;K. Nakayama;Shunsuke Ohtsubo;H. Higaki;H. Okamoto
本文提出了一种测量离子数相对较多的线性Paul陷阱中离子等离子体横向分布的诊断方法(∼107)。利用带有荧光屏的微通道板(MCP)将从陷阱中提取的等离子体的分布转换为光度分布，并使用电荷耦合器件(CCD)相机进行记录。成像系统的线性度是定量分析的基础，通过在很大的离子数范围内校正MCP增益的饱和来确保成像系统的线性度。通过数值模拟研究了陷阱内离子等离子体密度分布与MCP表面离子等离子体密度分布之间的对应关系。基于线性和对应关系，可以从观测到的光度分布中准确地重建陷阱中的密度分布。此外，还可以从观测到的横向密度分布确定横向温度和调谐压低。对等离子体横向分布的详细测量是利用离子陷阱对空间电荷为主的束流中各种集体效应进行实验研究的基础。作为成像诊断系统观测的一个例子，我们还演示了缓冲气体冷却引起的等离子体横向分布的收缩。
This paper presents a diagnostic method to measure the transverse distribution of an ion plasma confined in a linear Paul trap with a relatively large number of ions (∼107). The distribution of the plasma extracted from the trap is converted to a luminosity distribution using a microchannel plate (MCP) with a phosphor screen, and it is recorded with a charge-coupled device (CCD) camera. The linearity of the imaging system, which is the basis of the quantitative analyses, is ensured by correcting the saturation of MCP gain over a wide range of ion number. The correspondence between the density profile of an ion plasma in the trap and that at the MCP surface is examined by numerical simulation. The density profile in the trap can be reconstructed accurately from the observed luminosity distribution based on the linearity and the correspondence. Moreover, the transverse temperature and the tune depression can also be determined from the observed transverse density profile. The detailed measurement of the transverse plasma distribution is essential for the experimental study of various collective effects in space-charge-dominated beams using the ion trap. As an example of observations by the imaging diagnostic system, we also demonstrate the shrinking of the transverse plasma distribution by buffer-gas cooling.