Search

Properties of extreme ultraviolet (EUV) and particle emissions from laser-produced tin (Sn) plasma were experimentally investigated for use in industrial applications. Dependence of EUV emission on the initial thickness of Sn overcoat on a plastic sphere was studied to clarify the minimum mass needed to keep sufficient conversion to EUV and minimize plasma debris. EUV emission from low-density targets showed narrower spectra peaked at 13.5 nm, attributed to reduction of satellite line emissions in the spectrum foot and opacity broadening at the peak. It is shown that not only the EUV generation but also ion spectra are significantly affected by the Sn coat thicknesses.

A 10-kJ PW laser (LFEX) is under construction for the FIREX-I program. This paper reports a design overview of LFEX, the technological development of a large-aperture arrayed amplifier with modified four-pass architecture, wavefront correction, a large-aperture Faraday rotator with a superconducting magnet, a new pulse compressor arrangement, and focus control.

The typical specifications of the laser driver for a commercial IFE power plant are (1) total energy (MJ/pulse) with a tailored 20-40 ns pulse, (2) repetition operation (∼10 Hz), (3) efficiency (∼10%) with enough robustness and low cost. The key elements of the DPSSL driver technology are under development with HALNA. The HALNA 10 (High Average-power Laser for Nuclear-fusion Application) demonstrated 10 J $\times$10 Hz operation and the HALNA 100 (100 J $\times$10 Hz) is now under construction. By using the high average power and high intensity lasers, new industrial applications are being proceeded. The collaborative process for the development of high power laser with industry and for the industrial applications is effective and essential in the development of the laser driver for IFE power plant.

We have been developing an EUV light source by laser-produced plasma for the use of EUV lithography system under the Leading Project promoted by MEXT. The project aims at understanding physics of laser plasma EUV source and providing database and guidelines for the practical EUV source. Progresses in theoretical modeling and experimental results are briefly reported.

A coupled PIC and Fokker-Planck hierarchical simulation model for analysis of fast ignition core heating was checked by comparing the heating profile with collisional PIC simulations. The integrated simulations using FI3code were carried out for the recent fast heating experiments and showed that the dense core ($\rho > 10$g/cc) is heated up to 0.45 keV by the fast electrons via the Coulomb interactions (not anomalous processes).

The fast ignition is an epoch-making scheme for inertial fusion energy. In this scheme, the formation of high-density DT fuel is one of the key issues which must be solved, because the implosion dynamics of the fast ignition target which is non-spherical with conical target is quite different from that of the conventional central ignition target. Some previous works showed the possibility of formation of high density core. But the effects of hydrodynamic instability and DT cryogenic target were not discussed in those works. In this paper, we simulate the whole implosion dynamics of a perturbed non-spherical DT cryogenic target, and evaluate the possibility of formation of high-density DT fuel using 2-D integrated implosion code PINOCO.

We experimentally studied relativistic laser propagation in preplasmas at the highest powers ever attempted-0.2 to 0.4 petawatt. We demonstrated a single conical-shaped plasma channel formation extending several hundred microns in length from the under dense to over dense plasmas, indicating whole-beam self-focused laser channeling into the high-density plasma. The channel cone was reproduced by a three dimensional particle-in-cell simulation. The confirmation of the relativistic laser channeling into high-density plasmas holds the promise of fast igniting a highly compressed fuel plasma core.

The hot electron generation by irradiation of intense short laser pulses onto cone targets is studied by using 2D PIC simulation. It is shown that the high energy electrons from the cone target are characterized with three effective temprature, while two-temperature for plane target. The electrons composing most energetic component are generated at the cone tip where laser field is intensified by cone-guiding, and electrons for middle component are generated at cone wing which is not observed for plane target. The acceleration processes at cone wing, cone tip, and rear surface are explained.

Our institute has been investigating laser-produced tin, lithium and xenon plasma for extreme ultraviolet (EUV) light source of EUV lithography system, and found the highest conversion efficiency of 3% at 13.5 nm in 2% bandwidth. In the present paper, we introduce fabrication methods of density-controlled tin targets to generate relatively monochromatic EUV, and higher conversion efficiency than bulk tin. The first method is the nano-template method, where liquid tin solution was immersed into a polymer film with monodispersed size nanoparticle. The density can be controlled by tin concentration of the solution. The target can be classified into mass-limited target. We have shown a tendency of monochromatic EUV emission around 13.5 nm with decreasing of tin density. The intensity was higher than tin foil with bulk density. The tendency has a merit to mitigate heat effect of the first EUV mirror. The fabrication method has another merit to control not only density but also the poresize of tin oxide to be 100 nm ∼10 μm. The second is liquid crystalline template method to obtain porous tin oxide. The precursor with tin oxide and cellulose provides mechanically stable and transparent film. The film has wavy sub-microstructure derived from microscopic liquid crystal domain structure. The method is simple and short duration for the hydrolysis reaction to solidify tin compound. This material has a merit of feasibility of fabrication, and has been applied for rotation target for 10 Hz and 5 kHz laser repetition.

To investigate the core plasma heating in fast ignition targets, we recently developed a two-dimensional relativistic Fokker-Planck code “RFP-2D” for fast electron transport in dense plasmas. In the present study, we have coupled RFP-2D with a 2D hydrodynamics code for bulk plasma and analyzed the core plasma heating by assuming a condition similar to that in the GXII-PW laser experiments at ILE. It was found that when the source beam electrons enter the dense core region with “low” (<1 MeV) average energy and a Super-Gaussian spatial distribution, the core plasma can be heated above 0.8 keV at maximum, which is almost the same temperature as measured in the experiments.

Nonlinear dynamics of relativistic electron current in dense plasmas has been investigated by using two-dimensional Fluid-Particle Hybrid code (FPH code). FPH simulations show that relativistic electron filaments are generated by the Welbel instability and merge each other to be self-organized. When the relativistic electron beam diameter is large and the total current is over 100 times Alfven limit current, many filaments are confined in the initial beam area. It is found that the number of relativistic electron filament decreases in proportion to t- 0.9in the fixed ion case. This asymptotic behavior is explained by the random motion of filaments driven by fluctuating magnetic fields.

At the Institute of Laser Engineering, Osaka University, we have obtained Ni-like x-ray lasers of various atomic number elements, including many shorter wavelength Ni-like lasing lines around 5nm. The saturated amplification of Ni-like Ag lasing line at the wavelength of 13.9nm have been observed. Using these x-ray lasers, we are preparing the application experiments such as probing a laser-produced plasma with an x-ray laser interferometer.

Including a density jump between a cone tip and imploded plasmas, we have performed preliminary FI3simulations for fast ignition with cone-guided targets, and found that the density gap with 2ncwas effective at heating the core. But this effect is not successful under the realistic parameters for recent fast ignition experiments. Even so, it was found that the core could be heated up to 0.44 keV, but we could not get core temperature observed in the experiments, 0.8 keV. From those results, it should be emphasizes that integrated simulations under realistic conditions are essential for the fast ignition research.

Target design and the fabrication scheme are discussed aiming an application for the future laser fusion reactor KOYO-F that has 4 modular chambers with a wet wall operated with fast ignition scheme. Gain estimation and load of fusion output from the non-symetric burn on the first wall are shown.

Polarization degree of helium-like Cl-Heαline (1s21S0- 1s2p 1P1) from a chrolinated triple-layer target was measured using a 130 fs laser pulse at 1017W/cm2. The polarization degree was given as a function of overcoat thickness. It was found that the emission from a layer closer to the target surface is polarized parallel to the surface direction whereas emission from a deeper region in perpendicular to the surface. The experimental result was analyzed using a two dimensional (2D) Maxwellian distribution function for hot electrons. Beam-like distribution was found in the depth of plasma.

We have developed a Vlasov-Fokker-Planck code to investigate the non-local electron transport in laser-produced plasmas. The new numerical scheme is derived in two-dimension by using the operator splitting method. The velocity distribution function is expanded into zeroth and first order Legendre polynomials. We describe our scheme and show the importance of the nonlocal electron transport in laser-produced plasmas, by calculated results.

To investigate the core plasma heating in fast ignition targets, we recently developed a two-dimensional relativistic Fokker-Planck code ?RFP-2D? for fast electron transport in dense plasmas. In the present study, we have coupled RFP-2D with a 2D hydrodynamics code for bulk plasma and analyzed the core plasma heating by assuming a condition similar to that in the GXII-PW laser experiments at ILE. It was found that when the source beam electrons enter the dense core region with ?low? (<1?MeV) average energy and a Super-Gaussian spatial distribution, the core plasma can be heated above 0.8?keV at maximum, which is almost the same temperature as measured in the experiments.

Nonlinear dynamics of relativistic electron current in dense plasmas has been investigated by using two-dimensional Fluid-Particle Hybrid code (FPH code). FPH simulations show that relativistic electron filaments are generated by the Welbel instability and merge each other to be self-organized. When the relativistic electron beam diameter is large and the total current is over 100 times Alfven limit current, many filaments are confined in the initial beam area. It is found that the number of relativistic electron filament decreases in proportion to t - 0.9 in the fixed ion case. This asymptotic behavior is explained by the random motion of filaments driven by fluctuating magnetic fields.

We experimentally studied relativistic laser propagation in preplasmas at the highest powers ever attempted-0.2 to 0.4?petawatt. We demonstrated a single conical-shaped plasma channel formation extending several hundred microns in length from the under dense to over dense plasmas, indicating whole-beam self-focused laser channeling into the high-density plasma. The channel cone was reproduced by a three dimensional particle-in-cell simulation. The confirmation of the relativistic laser channeling into high-density plasmas holds the promise of fast igniting a highly compressed fuel plasma core.

The hot electron generation by irradiation of intense short laser pulses onto cone targets is studied by using 2D PIC simulation. It is shown that the high energy electrons from the cone target are characterized with three effective temprature, while two-temperature for plane target. The electrons composing most energetic component are generated at the cone tip where laser field is intensified by cone-guiding, and electrons for middle component are generated at cone wing which is not observed for plane target. The acceleration processes at cone wing, cone tip, and rear surface are explained.

The fast ignition is an epoch-making scheme for inertial fusion energy. In this scheme, the formation of high-density DT fuel is one of the key issues which must be solved, because the implosion dynamics of the fast ignition target which is non-spherical with conical target is quite different from that of the conventional central ignition target. Some previous works showed the possibility of formation of high density core. But the effects of hydrodynamic instability and DT cryogenic target were not discussed in those works. In this paper, we simulate the whole implosion dynamics of a perturbed non-spherical DT cryogenic target, and evaluate the possibility of formation of high-density DT fuel using 2-D integrated implosion code PINOCO.

A coupled PIC and Fokker-Planck hierarchical simulation model for analysis of fast ignition core heating was checked by comparing the heating profile with collisional PIC simulations. The integrated simulations using FI3 code were carried out for the recent fast heating experiments and showed that the dense core (?> 10?g/cc) is heated up to 0.45?keV by the fast electrons via the Coulomb interactions (not anomalous processes).

Properties of extreme ultraviolet (EUV) and particle emissions from laser-produced tin (Sn) plasma were experimentally investigated for use in industrial applications. Dependence of EUV emission on the initial thickness of Sn overcoat on a plastic sphere was studied to clarify the minimum mass needed to keep sufficient conversion to EUV and minimize plasma debris. EUV emission from low-density targets showed narrower spectra peaked at 13.5?nm, attributed to reduction of satellite line emissions in the spectrum foot and opacity broadening at the peak. It is shown that not only the EUV generation but also ion spectra are significantly affected by the Sn coat thicknesses.

We have been developing an EUV light source by laser-produced plasma for the use of EUV lithography system under the Leading Project promoted by MEXT. The project aims at understanding physics of laser plasma EUV source and providing database and guidelines for the practical EUV source. Progresses in theoretical modeling and experimental results are briefly reported.

Our institute has been investigating laser-produced tin, lithium and xenon plasma for extreme ultraviolet (EUV) light source of EUV lithography system, and found the highest conversion efficiency of 3% at 13.5?nm in 2% bandwidth. In the present paper, we introduce fabrication methods of density-controlled tin targets to generate relatively monochromatic EUV, and higher conversion efficiency than bulk tin. The first method is the nano-template method, where liquid tin solution was immersed into a polymer film with monodispersed size nanoparticle. The density can be controlled by tin concentration of the solution. The target can be classified into mass-limited target. We have shown a tendency of monochromatic EUV emission around 13.5?nm with decreasing of tin density. The intensity was higher than tin foil with bulk density. The tendency has a merit to mitigate heat effect of the first EUV mirror. The fabrication method has another merit to control not only density but also the poresize of tin oxide to be 100?nm ?10??m. The second is liquid crystalline template method to obtain porous tin oxide. The precursor with tin oxide and cellulose provides mechanically stable and transparent film. The film has wavy sub-microstructure derived from microscopic liquid crystal domain structure. The method is simple and short duration for the hydrolysis reaction to solidify tin compound. This material has a merit of feasibility of fabrication, and has been applied for rotation target for 10?Hz and 5?kHz laser repetition.

The typical specifications of the laser driver for a commercial IFE power plant are (1) total energy (MJ/pulse) with a tailored 20-40 ns pulse, (2) repetition operation (?10 Hz), (3) efficiency (?10%) with enough robustness and low cost. The key elements of the DPSSL driver technology are under development with HALNA. The HALNA 10 (High Average-power Laser for Nuclear-fusion Application) demonstrated 10 J ? 10 Hz operation and the HALNA 100 (100 J ? 10 Hz) is now under construction. By using the high average power and high intensity lasers, new industrial applications are being proceeded. The collaborative process for the development of high power laser with industry and for the industrial applications is effective and essential in the development of the laser driver for IFE power plant.

A 10-kJ PW laser (LFEX) is under construction for the FIREX-I program. This paper reports a design overview of LFEX, the technological development of a large-aperture arrayed amplifier with modified four-pass architecture, wavefront correction, a large-aperture Faraday rotator with a superconducting magnet, a new pulse compressor arrangement, and focus control.

Including a density jump between a cone tip and imploded plasmas, we have performed preliminary FI3 simulations for fast ignition with cone-guided targets, and found that the density gap with 2nc was effective at heating the core. But this effect is not successful under the realistic parameters for recent fast ignition experiments. Even so, it was found that the core could be heated up to 0.44?keV, but we could not get core temperature observed in the experiments, 0.8?keV. From those results, it should be emphasizes that integrated simulations under realistic conditions are essential for the fast ignition research.

Polarization degree of helium-like Cl-He? line (1s21S0 - 1s2p 1P1) from a chrolinated triple-layer target was measured using a 130 fs laser pulse at 1017 W/cm2. The polarization degree was given as a function of overcoat thickness. It was found that the emission from a layer closer to the target surface is polarized parallel to the surface direction whereas emission from a deeper region in perpendicular to the surface. The experimental result was analyzed using a two dimensional (2D) Maxwellian distribution function for hot electrons. Beam-like distribution was found in the depth of plasma.

We have developed a Vlasov-Fokker-Planck code to investigate the non-local electron transport in laser-produced plasmas. The new numerical scheme is derived in two-dimension by using the operator splitting method. The velocity distribution function is expanded into zeroth and first order Legendre polynomials. We describe our scheme and show the importance of the nonlocal electron transport in laser-produced plasmas, by calculated results.

Target design and the fabrication scheme are discussed aiming an application for the future laser fusion reactor KOYO-F that has 4 modular chambers with a wet wall operated with fast ignition scheme. Gain estimation and load of fusion output from the non-symetric burn on the first wall are shown.

We review the present status of fast ignition research. Since 1997, the fast ignition experiment and theory have been extensively continued at the Institute of Laser Engineering of Osaka University. In particular, the cone-shell target experiments and simulation research have made progress. In order to demonstrate heating of imploded high density plasma to the ignition temperature, in the April of 2003, the construction of heating laser of 10 kJ/10 ps/1.06 m (Laser for Fusion Experiment; LFEX), for FIREX-I (Fast Ignition Realization Experiment) has started. The fabrication of DT foam cryogenic cone target is also under development as a collaboration program between Osaka University and NIFS (National Institute for Fusion Science). The LFEX will be completed in 2008. After the completion of LFEX, the foam cryogenic cone shell target experiment will start in 2008. As a new approach toward compact ignition, an impact fusion scheme has been proposed, where the ablative acceleration to the order of 108cm/sec is the key issue. The ablation acceleration related to impact fusion has been explored by experiments.

We review the present status of fast ignition research. Since 1997, the fast ignition experiment and theory have been extensively continued at the Institute of Laser Engineering of Osaka University. In particular, the cone-shell target experiments and simulation research have made progress. In order to demonstrate heating of imploded high density plasma to the ignition temperature, in the April of 2003, the construction of heating laser of 10?kJ/10?ps/1.06?m (Laser for Fusion Experiment; LFEX), for FIREX-I (Fast Ignition Realization Experiment) has started. The fabrication of DT foam cryogenic cone target is also under development as a collaboration program between Osaka University and NIFS (National Institute for Fusion Science). The LFEX will be completed in 2008. After the completion of LFEX, the foam cryogenic cone shell target experiment will start in 2008. As a new approach toward compact ignition, an impact fusion scheme has been proposed, where the ablative acceleration to the order of 108?cm/sec is the key issue. The ablation acceleration related to impact fusion has been explored by experiments.