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激光等离子体在螺线管发散磁场中的特性研究

Characteristics of Laser Ablation Plasma in the Diverging Magnetic Field of a Solenoid

  • 摘要: 激光烧蚀等离子体(LAP)可用作粒子加速器和离子注入器中使用的离子源。相较于其它离子源,激光离子源在流强上具有优势,但由于产生的离子束脉冲时间短,限制了其在加速器中的广泛应用。实验中通过对激光等离子体扩散区域引入螺线管磁场进行约束,实现了对激光等离子体脉冲时间结构的调制。为了研究螺线管磁场对LAP的影响,实验使用了不同的激光能量(1~8 J)来生产具有不同初始条件的激光等离子体,并应用了不同的磁场强度来约束激光等离子体。在螺线管边缘场,通过可移动的法拉第筒(FC)对激光等离子体的横向分布进行测量。对于不同初始状态的等离子体,随着磁场的增加,其离子脉冲的主要参数(脉冲总电荷量、峰值流强、脉宽)均呈现先上升后逐渐饱和的变化趋势。另外,在没有磁场的条件下,在所测量位置处,等离子体的横向呈均匀分布;而在磁场约束的条件下,等离子体明显向轴线聚集。以上实验结果对进一步了解磁约束激光等离子体的特性具有重要意义。

     

    Abstract: Laser ablation plasma(LAP) can be used as an ion source for particle accelerators and for ion implantation. Although the too intensive current intensity of laser ion sources give them advantages over other ion sources, yet the minute duration of laser produced ion pulses limits their applications in accelerators. By introducing a solenoid into the plasma expansion region, the modulation of the plasma temporal structure had been achieved1-3. In order to study the effect of solenoid magnetic field on LAP, we used different laser energies (1~8 J) to produce LAP at different initial conditions and applied various magnetic field strengths to confine the plasma. The transverse distribution of the laser produced ions were measured with a movable faraday cup (FC) at the edge of the fringe field of the solenoid. The main parameters of the ion pulses, the total charge, the peak current, and the pulse duration, enhanced at first and then got saturated with the increasing magnetic field, no matter what the initial plasma conditions were. Unlike the nearly uniform transverse distribution of the plasma without magnetic confinement, the plasma got concentrated when the magnetic field was applied. The experimental results presented and discussed in the present work are of great significance for further understanding the characteristics of magnetically confined LAP.

     

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