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

本研究项目的目的是研制高效加热激光产生的等离子体的靶材，如X射线激光介质等离子体。假设平板目标受到双脉冲激光的照射。由于密度梯度的作用，预制等离子体的电子密度的空间分布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域的小区域而是外部区域，从而导致等离子体的无效加热。为了克服这一困难，我们提出了使用楔形靶的方法，在楔形靶中，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的内部，因此加热能量有望沉积在局域的小区域。2005年，利用流体力学模拟的方法设计了楔形靶的形状，并在JAEA中用CPA掺钛蓝宝石激光照射了楔形靶。将干涉仪和探针束背光源应用于预制等离子体的诊断，得到了电子密度空间分布的时间演化信息和主加热脉冲的最佳时间。2006年，我们在JAEA利用CPA掺钕玻璃激光器进行了实验：在最佳条件下，测量了楔形靶发射的连续谱X射线信号的空间分布：结果表明，与平板靶相比，楔形靶发射的能量范围为0.8-1.5KeV的X射线信号总量几乎增加了一个数量级。

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.