arXiv subjects

Tomoyuki Johzaki

Publications and source records attributed to Tomoyuki Johzaki.

9 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↗

arXiv2026

Probing In-Solid Proton Energy Distributions in Laser-Driven Fusion via Nuclear Activation Diagnostics

The energy distribution of energetic protons inside a solid target is a key quantity governing nuclear reaction yields and energy deposition in high-intensity laser-driven fusion, including nonthermal proton--boron (p--B) schemes and proton fast ignition. Yet it has remained inaccessible to conventional particle diagnostics, which detect only ions escaping the target and are perturbed by intense plasma electromagnetic fields. Here we establish a quantitative diagnostic that uses nuclear activation reactions occurring within the target itself as an internal probe of the in-solid proton energy distribution. Applied to laser-driven p--B fusion experiments on the kJ-class laser, the method reconstructs an exponential-equivalent in-solid proton energy distribution from the absolute yields of $^{11}\mathrm{C}$ and $^{7}\mathrm{Be}$ produced via $\mathrm{^{11}B(p,n)^{11}C}$ and $\mathrm{^{10}B(p,α)^{7}Be}$, and yields the absolute number of $\mathrm{^{11}B(p,2α)^{4}He}$ reactions through a side-channel analysis with propagated cross-section uncertainties. This work opens a quantitative window onto the in-solid proton dynamics that drive nuclear reactions in laser-driven fusion experiments.

physics.plasm-ph↗

arXiv2025

Enhancement of J x B electron acceleration with the micro-structured target and picosecond high-contrast relativistic-intensity laser pulse

Efficient generation of multi-hundred-keV electrons is essential for isochoric heating and can influence ion acceleration. We investigated electron acceleration from copper-oleate foil targets, either planar or coated with a gold mesh structure (bar width $5,μ\mathrm{m}$, spacing $7.5,μ\mathrm{m}$, thickness $\sim6,μ\mathrm{m}$), irradiated by $1.5$-ps, $350$-J LFEX laser pulses. Two laser-contrast conditions were examined: high ($\sim10^{10}$, with a plasma mirror) and low ($\sim10^{8}$, without a plasma mirror). Using Cu-K$_α$ emission mapping, we found that under high-contrast irradiation the micro-structured target enhanced the laser-to-electron conversion efficiency from $4.9\%$ to $14\%$, attributed to multiple internal reflections that strengthen $J\times B$ acceleration. In contrast, under low-contrast conditions the structures were filled with pre-plasma before the main pulse, and no enhancement was observed. These results demonstrate that both fine-scale structuring and high contrast are crucial for maximizing $J\times B$-driven electron generation in laser-plasma interactions. Our findings suggest a practical approach to improving laser-plasma coupling efficiency by exploiting micro-structured surfaces and contrast-controlled irradiation.

physics.plasm-ph↗

arXiv2025

Enhanced plasma heating via interaction with high-contrast laser and cone-shaped target

We investigated plasma heating enhancement using a high-intensity, high-contrast laser and a cone-attached target. Fast electron spectra and X-ray emission were measured with an electron spectrometer and a Bragg crystal spectrometer. The results were analyzed using PrismSPECT simulations with a two-component electron distribution model and empirical scaling laws. X-ray pinhole images showed that the cone effectively focused multi-spot laser light near its tip, enhancing local emission. While high-contrast laser irradiation reduced the fast electron slope temperature for flat targets, the use of a cone increased it by over threefold, corresponding to a fourfold rise in laser intensity. X-ray spectral analysis indicated an electron temperature of ~9~keV for the cone case, 17.5 times higher than that with a low-contrast laser. These findings demonstrate that combining high-contrast laser irradiation with cone-target geometry significantly improves laser energy coupling and plasma heating efficiency.

physics.plasm-ph↗

arXiv2019

Peta-Pascal Pressure Driven by Fast Isochoric Heating with Multi-Picosecond Intense Laser Pulse

Fast isochoric laser heating is a scheme to heat a matter with relativistic-intensity ($>$ 10$^{18}$ W/cm$^2$) laser pulse or X-ray free electron laser pulse. The fast isochoric laser heating has been studied for creating efficiently ultra-high-energy-density (UHED) state. We demonstrate an fast isochoric heating of an imploded dense plasma using a multi-picosecond kJ-class petawatt laser with an assistance of externally applied kilo-tesla magnetic fields for guiding fast electrons to the dense plasma.The UHED state with 2.2 Peta-Pascal is achieved experimentally with 4.6 kJ of total laser energy that is one order of magnitude lower than the energy used in the conventional implosion scheme. A two-dimensional particle-in-cell simulation reveals that diffusive heating from a laser-plasma interaction zone to the dense plasma plays an essential role to the efficient creation of the UHED state.

physics.plasm-ph↗

arXiv2018

Super-ponderomotive electron acceleration in blowout plasma heated by multi-picosecond relativistic intensity laser pulse

The dependence of the mean kinetic energy of laser-accelerated electrons on the laser intensity, so-called ponderomotive scaling, was derived theoretically with consideration of the motion of a single electron in oscillating laser fields. This scaling explains well the experimental results obtained with high-intensity pulses and durations shorter than a picosecond; however, this scaling is no longer applicable to the multi-picosecond (multi-ps) facility experiments. Here, we experimentally clarified the generation of the super-ponderomotive-relativistic electrons (SP-REs) through multi-ps relativistic laser-plasma interactions using prepulse-free LFEX laser pulses that were realized using a plasma mirror (PM). The SP-REs are produced with direct laser acceleration assisted by the self-generated quasi-static electric field and with loop-injected direct acceleration by the self- generated quasi-static magnetic field, which grow in a blowout plasma heated by a multi-ps laser pulse. Finally, we theoretically derive the threshold pulse duration to boost the acceleration of REs, which provides an important insight into the determination of laser pulse duration at kilojoule- petawatt laser facilities.

physics.plasm-ph↗

arXiv2017

Magnetized Fast Isochoric Laser Heating for Efficient Creation of Ultra-High-Energy-Density States

The quest for the inertial confinement fusion (ICF) ignition is a grand challenge, as exemplified by extraordinary large laser facilities. Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive and alternative approach to create ultra-high-energy-density states like those found in ICF ignition sparks. This avoids the ignition quench caused by the hot spark mixing with the surrounding cold fuel, which is the crucial problem of the currently pursued ignition scheme. High-intensity lasers efficiently produce relativistic electron beams (REB). A part of the REB kinetic energy is deposited in the core, and then the heated region becomes the hot spark to trigger the ignition. However, only a small portion of the REB collides with the core because of its large divergence. Here we have demonstrated enhanced laser-to-core energy coupling with the magnetized fast isochoric heating. The method employs a kilo-tesla-level magnetic field that is applied to the transport region from the REB generation point to the core which results in guiding the REB along the magnetic field lines to the core. 7.7 $\pm$ 1.3 % of the maximum coupling was achieved even with a relatively small radial area density core ($ρR$ $\sim$ 0.1 g/cm$^2$). The guided REB transport was clearly visualized in a pre-compressed core by using Cu-$K_α$ imaging technique. A simplified model coupled with the comprehensive diagnostics yields 6.2\% of the coupling that agrees fairly with the measured coupling. This model also reveals that an ignition-scale areal density core ($ρR$ $\sim$ 0.4 g/cm$^2$) leads to much higher laser-to-core coupling ($>$ 15%), this is much higher than that achieved by the current scheme.

physics.plasm-ph↗

arXiv2017

Kinetic modeling of x-ray laser-driven solid Al plasmas via particle-in-cell simulation

Solid-density plasmas driven by intense x-ray free-electron laser (XFEL) radiation are seeded by sources of non-thermal photoelectrons and Auger electrons that ionize and heat the target via collisions. Simulation codes that are commonly used to model such plasmas, such as collisional-radiative (CR) codes, typically assume a Maxwellian distribution and thus instantaneous thermalization of the source electrons. In this study, we present a detailed description and initial applications of a collisional particle-in-cell code, PICLS, that has been extended with a self-consistent radiation transport model and Monte-Carlo models for photoionization and KLL Auger ionization, enabling the fully kinetic simulation of XFEL-driven plasmas. The code is used to simulate two experiments previously performed at the Linac Coherent Light Source investigating XFEL-driven solid-density Al plasmas. It is shown that PICLS-simulated pulse transmissions using the Ecker-Kröll continuum-lowering model agree much better with measurements than do simulations using the Stewart-Pyatt model. Good quantitative agreement is also found between the time-dependent PICLS results and those of analogous simulations by the CR code SCFLY, which was used in the analysis of the experiments to accurately reproduce the observed Kα emissions and pulse transmissions. Finally, it is shown that the effects of the non-thermal electrons are negligible for the conditions of the particular experiments under investigation.

physics.plasm-ph↗

arXiv2004

Integrated Fast Ignition Simulation of Cone-guided Targetwith Three Codes

It was reported that the fuel core was heated up to ~ 0.8 [keV] in the fast ignition experimentswith cone-guided targets, but they could not theoretically explain heating mechanisms and achievement of such high temperature. Thus simulations should play an important role in estimating the schemeperformance, and we must simulate each phenomenon with individual codes and integrate them under the Fast Ignition Integrated Interconnecting code project. In the previous integrated simulations, fast electronsgenerated by the laser-plasma interaction were too hot to efficiently heat the core and we got only 0.096 [keV] temperature rise. Including the density gap at the contact surface between the cone tip and theimploded plasma, the period of core heating became longer and the core was heated by 0.162 [keV], ~69% higher increment compared with ignoring the density gap effect.

physics.plasm-ph↗