arXiv subjects

Katsunobu Nishihara

Publications and source records attributed to Katsunobu Nishihara.

6 recordsLinked to original sources

arXiv2026

Optimization of EUV output by experimentally validated radiation-hydrodynamic simulations across a broad laser parameter space

Practical requirements such as improving wall-plug efficiency and reducing system footprint have become increasingly important with the introduction of extreme ultraviolet (EUV) lithography into high-volume semiconductor manufacturing. These demands motivate the development of solid-state mid-infrared lasers as alternatives to current CO2 lasers. Systematic exploration of laser-to-EUV conversion efficiency (EUV-CE) over a broad parameter space is essential when altering the drive laser's wavelength, because the EUV-CE depends on the laser parameters in a complex manner. In this work, we performed a large-scale grid search of more than 140,000 parameter combinations for laser-produced tin plasma EUV sources using the radiation-hydrodynamics code STAR-1D, which is validated against EUV source experiments. The systematic wavelength dependence of the optimum pulse width and target size is governed by the requirement to simultaneously achieve the electron temperature and density optimal for EUV emission, maintain efficient laser absorption, and suppress EUV self-absorption. The resulting CE map predicts a global maximum of 5.63% at 5.5 μm. For the practically relevant 2 μm solid-state driver, a maximum CE of 4.64% is obtained, in good agreement with recent experimental results. Multiple operating points are identified over a broad range of pulse parameters, providing guidance for 2 μm-driven EUV source development.

physics.plasm-ph↗

arXiv2013

Critical Magnetic Field Strength for Suppression of the Richtmyer-Meshkov Instability in Plasmas

The critical strength of a magnetic field required for the suppression of the Richtmyer-Meshkov instability (RMI) is investigated numerically by using a two-dimensional single-mode analysis. For the cases of MHD parallel shocks, the RMI can be stabilized as a result of the extraction of vorticity from the interface. A useful formula describing a critical condition for MHD RMI has been introduced, and which is successfully confirmed by the direct numerical simulations. The critical field strength is found to be largely depending on the Mach number of the incident shock. If the shock is strong enough, even low-$β$ plasmas can be subject to the growth of the RMI.

physics.plasm-ph↗

arXiv2013

Prepulse and amplified spontaneous emission effects on the interaction of a petawatt class laser with thin solid targets

When a finite contrast petawatt laser pulse irradiates a micron-thick foil, a prepulse (including amplified spontaneous emission) creates a preplasma, where an ultrashort relativistically strong portion of the laser pulse (the main pulse) acquires higher intensity due to relativistic self-focusing and undergoes fast depletion transferring energy to fast electrons. If the preplasma thickness is optimal, the main pulse can reach the target generating fast ions more efficiently than an ideal, infinite contrast, laser pulse. A simple analytical model of a target with preplasma formation is developed and the radiation pressure dominant acceleration of ions in this target is predicted. The preplasma formation by a nanosecond prepulse is analyzed with dissipative hydrodynamic simulations. The main pulse interaction with the preplasma is studied with multi-parametric particle-in-cell simulations. The optimal conditions for hundreds of MeV ion acceleration are found with accompanying effects important for diagnostics, including high-order harmonics generation.

physics.plasm-ph↗

arXiv2012

Magnetic Field Amplification Associated with the Richtmyer-Meshkov Instability

The amplification of a magnetic field due to the Richtmyer-Meshkov instability (RMI) is investigated by two-dimensional MHD simulations. Single-mode analysis is adopted to reveal definite relation between the nonlinear evolution of RMI and the field enhancement. It is found that an ambient magnetic field is stretched by fluid motions associated with the RMI, and the strength is amplified significantly by more than two orders of magnitude. The saturation level of the field is determined by a balance between the amplified magnetic pressure and the thermal pressure after shock passage. This effective amplification can be achieved in a wide range of the conditions for the RMI such as the Mach number of an incident shock and the density ratio at a contact discontinuity. The results suggest that the RMI could be a robust mechanism of the amplification of interstellar magnetic fields and cause the origin of localized strong fields observed at the shock of supernova remnants.

astro-ph.HE↗

arXiv2004

A New Dynamical Domain Decomposition Method for Parallel Molecular Dynamics Simulation on Grid

We develop a new Lagrangian material particle -- dynamical domain decomposition method (MPD^3) for large scale parallel molecular dynamics (MD) simulation of nonstationary heterogeneous systems on a heterogeneous computing net. MPD^3 is based on Voronoi decomposition of simulated matter. The map of Voronoi polygons is known as the Dirichlet tessellation and used for grid generation in computational fluid dynamics. From the hydrodynamics point of view the moving Voronoi polygon looks as a material particle (MP). MPs can exchange particles and information. To balance heterogeneous computing conditions the MP centers should be dependent on timing data. We propose a simple and efficient iterative algorithm which based on definition of the timing-dependent balancing displacement of MP center for next simulation step. The MPD^3 program was tested in various computing environments and physical problems. We have demonstrated that MPD^3 is a high-adaptive decomposition algorithm for MD simulation. It was shown that the well-balanced decomposition can result from dynamical Voronoi polygon tessellation. One would expect the similar approach can be successfully applied for other particle methods like Monte Carlo, particle-in-cell, and smooth-particle-hydrodynamics.

cs.DC↗

arXiv2002

Three Dimensional Relativistic Electromagnetic Sub-cycle Solitons

Three dimensional (3D) relativistic electromagnetic sub-cycle solitons were observed in 3D Particle-in-Cell simulations of an intense short laser pulse propagation in an underdense plasma. Their structure resembles that of an oscillating electric dipole with a poloidal electric field and a toroidal magnetic field that oscillate in-phase with the electron density with frequency below the Langmuir frequency. On the ion time scale the soliton undergoes a Coulomb explosion of its core, resulting in ion acceleration, and then evolves into a slowly expanding quasi-neutral cavity.

physics.plasm-ph↗