用于直接驱动的快速变焦新方案

A novel fast zooming scheme for direct-driven laser fusion

在直接驱动方式的惯性约束聚变装置中,实现中心点火对靶丸的辐照均匀性要求极高.然而,在激光脉冲持续时间内,由于激光与靶丸的相互作用致使靶丸逐渐缩小,从而导致辐照均匀性降低以及交叉光束能量转移等不利因素增强,进而影响点火的进展.为此,提出了用于直接驱动的快速变焦新方案,即利用特殊设计的电光晶体及电极结构,对激光束附加一个实时、快速变化的球面波前,以控制打靶激光束的聚焦位置和焦斑大小,从而达到提高靶面辐照均匀性和抑制交叉光束能量转移的目的.通过建立快速变焦的理论模型,并基于激光与靶丸相互作用物理过程的分析,对焦斑尺寸、附加球面波曲率半径等参数随时间的变化规律进行了数值模拟和分析.结果表明,本文提出的快速变焦方案可有效地实现对焦斑与靶丸半径比的实时控制,且对空间滤波器滤波效果及三倍频转换效率并无明显影响.

Illumination uniformity of a target is highly required to achieve central ignition in inertial confinement fusion based on direct-driven fusion. However, the shell may be compressed due to its interaction with laser beams during the laser pulse duration, and may further result in the degradation of illumination uniformity and the enhancement of the cross-beam energy transfer （CBET）. Hence a novel fast zooming scheme for direct-driven laser fusion is proposed, i.e., by introducing the variable wavefront to the laser beam provided by a special-designed electro-optic crystal, thus the location and size of the focal spot could be controlled in real time, achieving the aim of improving the illumination uniformity and alleviating the CBET. This model of fast zooming has been built up, and variations of spot size and the radius of curvature of the additional spherical wavefront with time have been numerically simulated and analyzed based on the analysis of the interaction of the laser beam and the target. Results indicate that the fast zooming scheme could achieve effective and real-time control on the radius ratio between the focal spot and the target. Moreover, the fast zooming scheme has a little impact on the spatial filter capability and the third harmonic frequency conversion e？ciency.