A recently proposed octahedral spherical hohlraum with six laser entrance holes (LEHs) is an attractive concept for an upgraded laser facility aiming at a predictable and reproducible fusion gain with a simple target design. However, with the laser energies available at present, LEH size can be a critical issue. Owing to the uncertainties in simulation results, the LEH size should be determined on the basis of experimental evidence. However, determination of LEH size of an ignition target at a small-scale laser facility poses difficulties. In this paper, we propose to use the prepulse of an ignition pulse to determine the LEH size for ignition-scale hohlraums via LEH closure behavior, and we present convincing evidence from multiple diagnostics at the SGIII facility with ignition-scale hohlraum, laser prepulse, and laser beam size. The LEH closure observed in our experiment is in agreement with data from the National Ignition Facility. The total LEH area of the octahedral hohlraum is found to be very close to that of a cylindrical hohlraum, thus successfully demonstrating the feasibility of the octahedral hohlraum in terms of laser energy, which is crucially important for sizing an ignition-scale octahedrally configured laser system. This work provides a novel way to determine the LEH size of an ignition target at a small-scale laser facility, and it can be applied to other hohlraum configurations for the indirect drive approach.

提出了一种基于小压电陶瓷条的三角放大型微纳米驱动机构。该机构由两个1.6 mm×1.6 mm×5.0 mm的小压电陶瓷条、三角对称型伸缩臂、大顶角柔性铰链（扫描端）及基座组成，由小压电陶瓷条驱动伸缩臂运动，基于大顶角三角形的放大原理，获得高放大倍率的扫描端输出位移。理论分析与有限元仿真表明，当三角对称型伸缩臂与底边的夹角为6°时，扫描端的位移量与小压电陶瓷条的伸缩量之比可达9倍左右；当驱动电压为80 V时，相比于小压电陶瓷条的伸缩量3.2 μm，扫描端的位移量理论值可达29.5 μm。显微运动测量实验表明，在相同驱动电压下，扫描端的实际位移量达到26.6 μm，实际位移放大倍数达到8.3倍。将该机构作为原子力显微镜的慢轴扫描器，成功实现了基于小压电陶瓷条的宽范围原子力显微镜扫描成像（4 μm×26 μm），具有良好的分辨率、对比度和线性度。该机构具有原理新颖、结构简洁、成本低廉、性能优越等特点，可望在光学、精密机械及微纳米技术领域获得广泛的应用。