Experimental observation of low-order collective oscillation modes in a strong-focusing lattice
Experimental observation of low-order collective oscillation modes in a strong-focusing lattice
复制标题
强聚焦晶格中低阶集体振荡模式的实验观察
DOI：
10.1088/1742-6596/1350/1/012125
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
H Higaki and H Okamoto
中科院分区：
文献类型：
--
作者：
K Ito;T Kurauchi;H Higaki and H Okamoto
在传统的线性Paul阱（LPT）中，四个电极棒对称地放置在阱轴周围以产生用于横向离子约束的射频（rf）四极场。在特定条件下，外聚焦电势的周期性会导致严重的离子损失。损耗机制基本上与强流束动力学中众所周知的相干电子感应加速器共振相同[1，2]。事实上，在LPT中的离子等离子体的集体运动被示出为等效于带电粒子束穿过交变梯度（AG）聚焦晶格的集体运动。在本研究中，我们通过检测电极表面感应的镜像电流来直接测量LPT中的低阶相干振荡模式。LPT的四棒结构允许我们从等离子体束的偶极和四极振荡中拾取微弱信号。这些信号进行傅立叶分析，以评估在不同的初始离子密度的相干振荡调谐。测量的四极模的调谐被用来推断作为存储在LPT中的离子数的函数的调谐凹陷。
In a conventional linear Paul trap (LPT), four electrode rods are placed symmetrically around the trap axis to generate a radio-frequency (rf) quadrupole field for transverse ion confinement. The periodic nature of the external focusing potential can give rise to serious ion losses under a specific condition. The loss mechanism is essentially the same as the coherent betatron resonance well-known in intense beam dynamics [1, 2]. In fact, the collective motion of an ion plasma in the LPT is shown equivalent to that of a charged-particle beam traveling through an alternating-gradient (AG) focusing lattice. In the present study, we perform the direct measurement of low-order coherent oscillation modes in the LPT by detecting image currents induced on the electrodes' surfaces. The four-rod structure of the LPT allows us to pick up weak signals from the dipole and quadrupole oscillations of a plasma bunch. These signals are Fourier analyzed to evaluate the coherent oscillation tune at different initial ion densities. The measured tune of the quadrupole mode is used to deduce the tune depression as a function of ion number stored in the LPT.