国家点火装置波前控制系统
The Wavefront Control System for the National Ignition Facility
摘要：
国家点火装置（NIF）要求192束激光中的每一束的脉冲都以50 um rms的精度定位在目标上。光束质量必须足以将总计1.8 MJ的0.351-um光聚焦到600-um直径的体积中。最佳平坦光束波前可以实现这种指向和聚焦精度。控制系统通过在激光器对准期间执行闭环补偿来校正波前像差，以校正气体密度变化。闪光灯引起的热变形的静态补偿是在激光照射之前建立的。控制系统通过用77个小透镜哈特曼传感器测量波前并用39个致动器可变形反射镜进行校正来补偿10 Hz的每个激光束。分布式体系结构利用运行Solaris的MPERAAXi计算机执行传感器数据的实时图像处理，并利用运行MPERAWorks的基于PowerPC的计算机计算镜像命令。一对双CPU和PowerPC处理器完成一组八个光束的波前控制。软件设计采用了经过验证的自适应光学控制算法，该算法在多任务环境中实现，以经济地并行控制光束波前。原型测试已经实现了0.03波均方根的闭环剩余误差。
英文摘要：
The National Ignition Facility (NIF) requires that pulses from each of the 192 laser beams be positioned on target with an accuracy of 50 um rms. Beam quality must be sufficient to focus a total of 1.8 MJ of 0.351-um light into a 600-um-diameter volume. An optimally flat beam wavefront can achieve this pointing and focusing accuracy. The control system corrects wavefront aberrations by performing closed-loop compensation during laser alignment to correct for gas density variations. Static compensation of flashlamp-induced thermal distortion is established just prior to the laser shot. The control system compensates each laser beam at 10 Hz by measuring the wavefront with a 77-lenslet Hartmann sensor and applying corrections with a 39-actuator deformable mirror. The distributed architecture utilizes SPARC AXi computers running Solaris to perform real-time image processing of sensor data and PowerPC-based computers running VxWorks to compute mirror commands. A single pair of SPARC and PowerPC processors accomplishes wavefront control for a group of eight beams. The software design uses proven adaptive optic control algorithms that are implemented in a multi-tasking environment to economically control the beam wavefronts in parallel. Prototype tests have achieved a closed-loop residual error of 0.03 waves rms.
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