Kim Tae-Seong, Kim Jinchoon, In Sang Ryul, Jeong Seung Ho
University of Science and Technology, Daejeon, Republic of Korea.
Rev Sci Instrum. 2008 Feb;79(2 Pt 2):02A704. doi: 10.1063/1.2816921.
Prototype long pulse ion sources are being developed and tested toward the goal of a deuterium beam extraction of 120 keV/65 A. The latest prototype source consists of a magnetic bucket plasma generator and a four-grid copper accelerator system with multicircular apertures of 568 holes. To measure the angular divergence and the ion species of the ion beam, an optical multichannel analyzer (OMA) system for a Doppler-shifted H-alpha lights was set up at the end of a gas-cell neutralizer. But the OMA data are very difficult to analyze due to a large background level on the top of the three energy peaks (coming from H(+), H(2) (+), and H(3) (+)). These background spectra in the OMA signals seem to result from partially accelerated ion beams in the accelerator. Extracted ions could undergo a premature charge exchange as the accelerator column tends to have a high hydrogen partial pressure from the unused gas from the plasma generator, resulting in a continuous background of partially accelerated beam particles at the accelerator exit. This effect is calculated by accounting for all the possible atomic collision processes and numerically summing up three ion species across the accelerator column. The collection of all the atomic reaction cross sections and the numerical summing up will be presented. The result considerably depends on the background pressure and the ion beam species ratio (H(+), H(2) (+), and H(3) (+)). This effect constitutes more than 20% of the whole particle distribution. And the energy distribution of those suffering from collisions is broad and shows a broad maximum in the vicinity of the half and the third energy region.
正在开发和测试原型长脉冲离子源，目标是实现120 keV/65 A的氘束提取。最新的原型源由一个磁桶等离子体发生器和一个带有568个孔的多圆形孔径的四栅铜加速器系统组成。为了测量离子束的角发散和离子种类，在气室中和器末端设置了一个用于多普勒频移H-α光的光学多通道分析仪（OMA）系统。但是，由于三个能量峰（来自H(+)、H(2) (+)和H(3) (+)）顶部的背景水平很高，OMA数据很难分析。OMA信号中的这些背景光谱似乎是由加速器中部分加速的离子束产生的。由于加速器柱往往因等离子体发生器未使用的气体而具有较高的氢分压，提取的离子可能会过早发生电荷交换，导致加速器出口处部分加速束粒子的连续背景。通过考虑所有可能的原子碰撞过程并对加速器柱上的三种离子种类进行数值求和来计算这种效应。将展示所有原子反应截面的收集情况和数值求和结果。结果在很大程度上取决于背景压力和离子束种类比（H(+)、H(2) (+)和H(3) (+)）。这种效应占整个粒子分布的20%以上。并且遭受碰撞的粒子的能量分布很宽，在一半和三分之一能量区域附近呈现出一个宽的最大值。
