论文标题
MORA项目的透明轴对称离子陷阱的几何优化
Geometry optimisation of a transparent axisymmetric ion trap for the MORA project
论文作者
论文摘要
在Project Mora（MATER的起源中，来自被困和定向离子的无线电活动的起源），设计了透明的轴向对称射频离子陷阱（Moratrap），以衡量核$ $ $β-$β-$β-$β-激光型离子的三重相关参数$ d $。陷阱设计的灵感来自于2005年至2013年在Ganil运行的LPCTRAP几何形状。在实际（非理想的）Paul Trap中，四极电位的电位并不是完美的，从而导致离子运动的不稳定性，因此影响整体陷阱效率。本文提出了一种旨在优化陷阱几何形状的数值方法。它应用于moratrap，以提高捕获效率并与LPCTRAP相比扩大轴向透明的实体角度。在整个优化过程中，使用基于边界元素方法（BEM）的静电求解器对电势和场进行数值计算。优化包括根据电势的高阶多物来最大程度地减少目标函数（适应性函数）。最后，应用陷阱维度和电极位移的系统变化以研究对潜在质量的几何影响。
In the frame of the project MORA (Matter's Origin from the Radio Activity of trapped and oriented ions), a transparent axially symmetric radio-frequency ion trap (MORATrap) was designed in order to measure the triple correlation parameter $D$ in nuclear $β-$decay of laser-polarised ions. The trap design was inspired from the LPCTrap geometry, operated at GANIL from 2005 to 2013. In a real (non-ideal) Paul trap, the quadrupole electric potential is not perfect leading to instabilities in ion motion and therefore affecting the overall trapping efficiency. This paper presents a numerical method aiming to optimise the geometry of a trap. It is applied to MORATrap in order to improve the trapping efficiency and to enlarge the axial transparent solid angle compared to LPCTrap. In the whole optimisation process, numerical computation of electric potential and field was carried out using an electrostatic solver based on boundary element method (BEM). The optimisation consisted in minimising an objective function (fitness function) depending on higher order multipoles of the potential. Finally, systematic changes of trap dimensions and electrode displacements were applied to investigate geometrical effects on the potential quality.
