Search

Suppression of hydrodynamic instabilities is very crucial for the ultimate goal of inertial fusion energy (IFE). A high-Z doped plastic of CHBr (brominated polystyrene) ablator is a very promising candidate to suppress the ablative Rayleigh-Taylor (RT) instability in a directly laser-driven IFE target. When a CHBr target is irradiated by intense laser beams, bromine atoms in the corona plasma emit strong radiation. The strong radiation drives the radiative ablation front inside the CHBr targets. This radiative ablation in the high-Z doped plastic target has many advantages for the suppression of the growth of the RT instability in analogy to the indirect-drive approach, i.e., large mass ablation rate, long density scale length and low peak density. Two-dimensional (2D) hydrodynamic simulation shows significant suppression of the RT instability in a CHBr target compared to an undoped polystyrene (CH) target. RT growth rate, calculated theoretically using the Betti-Goncharov procedure with a one-dimensional radiation-hydrodynamic simulation code, is in good agreement with the 2D calculations. Experiments were performed at the GEKKO XII- [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)] HIPER (High Intensity Plasma Experimental Research) laser facility. The trajectory of a laser-driven CHBr target observed in the experiment was reproduced fairly well by the simulation. The radiative ablation front formed inside a directly laser-driven CHBr target was clearly observed for the first time. The strong suppression of the RT instability in the CHBr target was confirmed using the face-on and side-on x-ray backlighting technique. The high-Z doped ablator can be applied to high density cryogenic deuterium-deuterium and deuterium-tritium compression, because the hydrogen-isotopes are nearly transparent to x rays, which are transmitted through the ablator from the laser-irradiation side. [ABSTRACT FROM AUTHOR]

We developed and improved high space- and time-resolution x-ray imaging techniques (3-6 µm, 100-200 ps). These techniques were coupled with side-on x-ray backlighting for observing hydrodynamics of directly laser-driven polystyrene plasmas. As a high sensitive x-ray image detector, Imaging Plate was introduced to penumbral imaging technique [S. Fujioka et al., Rev. Sci. Instrum. 73, 2588 (2002)]. Noise in penumbral images was reduced by this improvement, and high quality density profiles of plasmas were obtained. A large-magnification slit camera, whose slit width and magnification were 4 µm and 82.8, was coupled with an x-ray streak camera (XSC). Due to the advantage of the large-magnification, high spatial resolution of 5.8 µm was found even with an XSC, the photocathode of which usually has low spatial resolution. These techniques are useful in understanding of hydrodynamic instability in inertial confinement fusion. [ABSTRACT FROM AUTHOR]

Rayleigh-Taylor (RT) instability is one of the most important physical issues in the inertial confinement fusion research. The reduction of its growth rate due to laser-driven ablation, which is described by the modified Takabe formula, is of great importance for a precise understanding of the target physics. We have developed various diagnostic techniques for the measurement of the parameters appearing in the Takabe formula, such as the growth rate, the acceleration, the mass ablation rate, and the density structure including ablation density and density scalelength. Face-on and side-on x-ray backlighting were coupled with moire interferometry imaging, penumbral imaging, and Fresnel zoneplate imaging. All the physical parameters related to RT instability were measured experimentally, and compared with simulation results. [ABSTRACT FROM AUTHOR]

In study of hot and dense plasma, a high spatial resolution (a few microns) x-ray imaging is very important to observe these plasmas. The Fresnel phase zone plate (FPZP) consists of alternately material and transparent circular annuli placed concentrically, which image x rays using diffraction x rays from all annuli. FPZP have imaged 4.7–4.77 keV x rays with 2.2 μm spatial resolution. However FPZP has a problem that background level is comparable to signal level. In subtraction of background, the error of 10% is caused. For the accurate background subtraction, we designed new FPZP, which consist of three β layers of a transparent zone and two material zones. The new design FPZP parameters (thickness of material zones, each zone width) have been optimized, and in that optimum design signal-to-background ratio is 4 times better than conventional two layers FPZP. [ABSTRACT FROM AUTHOR]