In this study, we use the FLASH radiation hydrodynamic code and the FLYCHK atomic code to investigate the energy conversion and spectra associated with laser–Sn target interactions with 1 and 2 µm wavelength lasers. We found that the conversion efficiency (CE) reached as much as 3.38% with the 2 µm laser, which is 1.48 percentage points higher than the 1 µm laser (CE = 1.9%). In addition, we analyzed the contribution of dominant ionization states to the emission spectrum for both lasers. We observed that the growths of the out-of-band emission eventually led to a broadening of the spectrum, resulting in a reduction of spectral purity for the 1 µm laser. By contrast, the emission main peaks were all centered near 13.5 nm for the 2 µm laser, which is beneficial for efficient emission of light with a 13.5 nm wavelength (relevant for nanolithographic applications).
Quasi-isentropic compression is required for inertial confinement fusion (ICF) to compress the target to a high density and high temperature status, where to match the laser pulse shape and target structure is of great significance to the implosion. However, many parameters for the laser pulse shape and the target structure should be optimized in order to realize such match. In this paper, the drive laser pulse and the target structure are designed using a random optimization method for a direct-drive ICF implosion driven by a 358.40 kJ laser pulse. This method can quickly optimize the laser pulse and target structure parameters for an efficient quasi-isentropic compression of the plasmas, leading to an areal density of 9.30% higher than that given by the hydrodynamic scaling. A correlation matrix is also constructed to analyze the correlation between the parameters. This provides a reference for further optimization and improvement. The method should have potential applications in the target design for future ICF experiments.
Fuel magnetization significantly lowers the required radial convergence, enabling cylindrical implosions to become a promising approach for inertial confinement fusion. The Nernst effect on the two-layer single shell magnetized target design applied to a Z-pinch benefits from a gold layer that decreases fuel demagnetization and serves as a magnetothermal insulation layer, preventing magnetothermal losses. The resistive diffusion and Nernst advection of the magnetic field are considered in the radiation magnetohydrodynamic model, which alter the evolution of magnetic flux in the magnetized target and result in plasma demagnetization. The results demonstrate that targets with a wide range of parameters can achieve ignition conditions under a 30 MA driven current. A two-layer single shell magnetized target for lessening the Nernst effect has the potential to achieve ignition conditions. The fusion yield of the optimal target increases by 168% from 0.71 MJ to 1.90 MJ, compared to a one-layer single shell target.
12 October 2021 in Plasma Physics and Controlled Fusion
High-gain magnetized liner inertial fusion (MagLIF) is a possible way to realize fusion. To investigate electrothermal effects on the transport of magnetic flux and thermal flux in MagLIF, this study has developed a resistive magnetohydrodynamics (MHD) module including an axial magnetic field using the code MULTI-IFE. MagLIF driven by a peak current of 60 MA releases 1080 MJ of fusion energy for a 1 cm-long liner, corresponding to an energy gain of approximately 180. The magnetic field is decompressed by electrothermal effects owing to the great temperature gradient in the fuel. This papers shows that a Nernst flux limiter of between 0.1 and 0.3 prevents the Nernst velocity from significantly decompressing the axial magnetic field and achieving a relative high yield. Compared with that of a simple gas target, the magnetic flux loss in the high-gain MagLIF target can be reduced from 70% to 30% owing to the magnetic insulation in the cryogenic deuterium–tritium (DT). Most of the cryogenic DT layer in a high-gain MagLIF target is burned, resulting in a significant increase in the fusion yield.
A radiation magnetohydrodynamics algorithm has been developed to investigate Z-pinch magnetized liner inertial fusion process. In magnetized plasma, the electron temperature gradients transport magnetic flux in the direction opposite to that gradient, a phenomenon known as the Nernst effect. Analogously, magnetic field gradients drive electron heat flow in the gradient direction. Both transport mechanisms are included in this algorithm, and the governing differential equations are discretized in Lagrangian coordinates. This MHD algorithm has been integrated into the one-dimensional radiation hydrodynamics code, MULTI-IFE. Validation is performed using benchmark cases such as the Brio–Wu shock tube, magnetic flux transport driven by thermal gradients, and an application of Z-pinch MagLIF. The results provide a foundation for further exploration of MagLIF and other radiation MHD applications.