Investigation of the basic processes for the development of the target required for the local heating of plasma.

该研究项目的目的是开发专用于激光产生等离子体（如x射线激光介质等离子体）的有效加热的靶。考虑用双脉冲激光照射平面靶。预形成等离子体的电子密度的空间分布由于密度梯度而使主加热激光脉冲向外折射;因此，大量的加热能量不是沉积在局部的小区域，而是沉积在外部区域，这导致等离子体的无效加热。为了克服这个困难，我们提出使用楔形靶，其中，预形成的等离子体的电子密度分布将主加热激光脉冲引导到楔形物的内部，因此期望加热能量沉积在局部化的小区域中。2005年，利用流体力学模拟设计了楔形靶的形状，并利用日本原子能机构的CPA钛宝石激光器对楔形靶进行了辐照。利用探测光束的干涉仪和背光灯对预成形等离子体进行了诊断，获得了电子密度空间分布随时间的演化信息以及主加热脉冲的最佳定时。2006年，我们在日本原子能机构使用CPA Nd：glass激光器进行了实验：在最佳条件下，测量了楔形靶发射的连续X射线信号的空间分布：结果表明，采用楔形体后，能量范围为0.8-1.5KeV的X射线的总信号量几乎增加了一个数量级。形状目标与平面目标相比。

The aim of this research project is development of target dedicated to the efficient heating of laser-produced plasma such as x-ray laser medium plasma. Consider that a flat target is irradiated by double pulses of laser light. The spatial profile of the electron density of the pre-formed plasma refracts the main heating laser pulse in the outward direction due to the density gradient ; therefore substantial amount of heating energy is not deposited in the localized small area but outer region, which leads to the ineffective heating of the plasma.In order to overcome this difficulty, we propose the use of wedge-shape target, in which the electron density profile of the pre-formed plasma guides the main heating laser pulse to the inward of the wedge, therefore the heating energy is expected to be deposited in the localized small area. In 2005, the shape of the wedge target was designed by use of hydrodynamics simulation, and the target was irradiated by the CPA Ti : Sapphire laser in JAEA. The interferometer and backlighter using the probe beam was applied to the diagnostics of the pre-formed plasma, and we obtained the information of temporal evolution of the spatial profile of the electron density together with the optimum timing of the main heating pulse. In 2006, we have conducted the experiment using CPA Nd : glass laser in JAEA : under the optimum condition, the spatial profile of the continuum x-ray signal emitted from the wedge-shape target was measured : the result indicated that the total amount of signal of x-ray with the energy range of 0.8-1.5KeV is increased by virtually one-order of magnitude by employing the wedge-shape target compared with that of flat target.