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A counter-propagating laser-beam platform using a spherical plasma mirror was developed for the kilojoule-class petawatt LFEX laser. The temporal and spatial overlaps of the incoming and redirected beams were measured with an optical interferometer and an x-ray pinhole camera. The plasma mirror performance was evaluated by measuring fast electrons, ions, and neutrons generated in the counter-propagating laser interaction with a Cu-doped deuterated film on both sides. The reflectivity and peak intensity were estimated as ∼50% and ∼5 × 1018 W/cm2, respectively. The platform could enable studies of counter-streaming charged particles in high-energy-density plasmas for fundamental and inertial confinement fusion research.

Fast heating efficiency when a pre-imploded core is directly heated with an ultraintense laser (heating laser) was investigated. ‘Direct heating’ means that a heating laser hits a pre-imploded core without applying either a laser guiding cone or an external field. The efficiency, η, is defined as the increase in the internal core energy divided by the energy of the heating laser. Six beams (output of 1.6 kJ) from the GEKKO XII (GXII) green laser system at the Institute of Laser Engineering (ILE), Osaka University were applied to implode a spherical deuterated polystyrene (CD) shell target to form a dense core. The DD-reacted protons and the core x-ray emissions showed a core density of 2.8 ± 0.7 g cm−3, or 2.6 times the solid density. Furthermore, DD-reacted thermal neutrons were utilized to estimate the core temperature between 600 and 750 eV. Thereafter, the core was directly heated by a laser for fast-ignition experiments (LFEX, an extremely energetic ultrashort pulse laser) at ILE with its axis lying along or perpendicular to the GXII bundle axis, respectively. The former and latter laser configurations were termed ‘axial’ and ‘transverse modes’, respectively. The η was estimated from three independent methods: (1) the core x-ray emission, (2) the thermal neutron yield, and (3) the runaway hot electron spectra. For the axial mode, 0.8% < η < 2.1% at low power (low LFEX energy) and 0.4% < η < 2.5% at high power (high LFEX energy). For the transverse mode, 2.6% < η < 7% at low power and 1.5% < η < 7.7% at high power. Their efficiencies were compared with that in the uniform implosion mode using 12 GXII beams, 6% < η < 12%, which appeared near to the η for the transverse mode, except that the error bar is very large.

In the counter-irradiation, which is one of the fast ignition schemes, higher core energy coupling can be expected when there are two hot electron flows in counter directions. Two plasma mirrors were installed for the counter irradiation at about 180 degrees. The hot electron effective temperatures (Teff) were measured by using electron energy spectrometers. Teff vs the laser intensity on a foil target followed Wilkes' scaling law. The energy incident on the target could be calculated by estimating the laser intensity on the target from Teff and estimating the focusing radius from the X-ray pinhole camera image. As a result, the reflectivity could be estimated to be 17 ± 3%.

A laser inertial fusion energy (IFE) reactor requires repetitive injection of fuel pellets and laser engagement to fuse fusion fuel beyond a few Hz. We demonstrate 10 Hz free-fall bead pellet injection and laser engagement with γ-ray generation. Deuterated polystyrene beads with a diameter of 1 mm were engaged by counter illuminating ultra-intense laser pulses with an intensity of 5 × 1017 W cm−2 at 10 Hz. The spatial distribution of free-fall beads was 0.86 mm in the horizontal direction and 0.18 mm in the vertical direction. The system operated for more than 5 min and 3500 beads were supplied with achieved frequencies of 2.1 Hz for illumination on the beads and 0.7 Hz for γ-ray generation; these frequencies were three times greater than with the previous 1 Hz injection system. The duration of operation was limited by the pellet supply. This injection and engagement system could be used for laser IFE research platforms.

The injection and engagement of pellets using laser beam irradiation is one of the key technologies to realize a laser-driven inertial fusion energy (IFE) reactor. We irradiated ultra-intense laser...

A neutron generator is developed using 1-mm-diam spherical deuterated polystyrene targets on a rotating disk irradiated with an ultrahigh-intensity (>1018 W/cm2) diode-pumped laser. It consists of ...

The discussion how to accelerate electrons to GeV leads us to the concept of the capillary. The 40 TW laser with prepulses, guided into a 1 cm-long capillary has accelerated the electrons to 100 MeV. The prepulse-free PW laser was also guided into the longer capillary, which formed a 3 cm plasma channel, but the energy gain was only 40 MeV. The prepulse-free laser made it clear that the cone works as an electron seeder. Application of the capillary accelerator was finally discussed.

Ultra intense laser interaction with solids is crucially modified by the presence of the plasma layer created by the prepulse associated with the peak intensity pulse. Here interferometric measurements of the preplasma created by a 40 TW, 600 fs Nd-glass laser are reported. Density profile and its target dependence are measured and the predicted scale length dependence on target atomic number is confirmed.

The dependence of neutron spectra on the incident laser polarization has been studied to elucidate ion acceleration processes in ultra-intense laser–plasma interactions. Obliquely incident, 50–100 TW (450–800 fs) laser pulses irradiated a deuterated plastic solid target at 1019 W/cm2 with both s- and p-polarizations. Neutron spectra from the deuteron–deuteron d(d,n)3He nuclear reactions show the ion acceleration into the target in the direction of the target normal for both polarizations. The experiment and particle-in-cell simulations indicate the ions are accelerated inside the target by an intense electrostatic field created by charge displacement at the laser focus.

Basic and integrated studies are conducted on fast ignition (FI) using various large laser systems. A Peta watt (PW) laser system is used to study the basic elements relevant to FI and can also be injected to a compressed core to test the FI integrated experiment when coupled with a GEKKO twelve laser beam system. Using a spherical target inserted with a Au cone guide for the PW laser pulse, an imploded core is heated up to 1 keV resulting in neutron increase 1000 times more than that without heating pulse. Details of the implosion are examined at the Omega laser system of this type target with indirect implosion scheme and are compared with simulation results. LASNEX simulation indicates that a 400 g/c.c. high density core could be achieved with this scheme at 1.8 MJ laser input.

Under the action of an intense laser and strong magnetic field, an electron undergoes oscillation at a cyclotron frequency, as well as the frequency of the incident wave. The coupling between the drift cyclotron and figure-8 motions can generate sidebands in the vicinity of all harmonics. The frequency separation between the sidebands could be used to infer the magnitude of the self-generated magnetic field.

Stimulated Raman scattering (SRS) from a mm-scale inhomogeneous plasma irradiated with an ultra-intense laser pulse was studied. Experimental results show that backward SRS spectral intensities increase with scattered light wavelength up to 1.3 λ0 and saturate at longer wavelength, where λ0 is the wavelength of the ultra-intense laser. Nonlinear phase mismatch was found to cause the saturation from a fully relativistic nonlinear 1D fluid simulation due to the relativistic mass increase of electron. The total amount of SRS was measured to be less than 3% of the incident laser energy.

The spectrum of transition radiation from a relativistic hot electron beam with the Boltzmann energy distribution is theoretically studied. The spectrum of transition radiation is separated into two parts: one is the incoherent spectrum, the other is the coherent spectrum. The results show that the temperature and total number of hot electrons can be obtained from the incoherent spectrum, and that the perturbation wave number in an electron bunch can be deduced from the coherent spectrum, from which the dominant heating process can be studied.

Modern high-power lasers can generate extreme states of matter that are relevant to astrophysics, equation-of-state studies and fusion energy research. Laser-driven implosions of spherical polymer shells have, for example, achieved an increase in density of 1,000 times relative to the solid state. A new laser technology ‘ultra-intense’ laser is now opening a new ground of the laser fusion research, which is called as fast ignition. During the last several years, we have extensively studied elementary physics relevant to the fast ignitor. Based on these results, we have succeeded enforced heating of imploded plasmas with a 100 TW laser as the first demonstration of this new approach. The experimental result implies the future possibility of breakeven and ignition with significantly small laser energies. This new approach provides a route toefficientfusionenergy production.

CR-39 film stacks are used to measure the energy and angular distribution of protons emitted from the rear surface of ultra-intense laser illuminated plastic foils. The experiment suggests that the energetic protons are dragged away from the rear surface, where the hot electron formed a virtual cathode. The two-dimensional particle in cell simulation supports this hypothesis. For 5 (100) μm thick target, 1.8×109 protons have a slope temperature of 3 (2) MeV. The ring structure of proton emission leads us to the hypothesis that a toroidal magnetic field associated with the hot electrons works on the fast ions and deflects them. From the logarithmic slope of the ring diameter versus the ion energy, the product of the magnetic field × the length over which it works on the ions is estimated to be up to 1000 MG⋅μm. The simulation shows that a strong toroidal magnetic field was excited at the target rear side with expansion of plasmas. The proton’s angular distribution from the rear surface has the logarithmic ...

The back-reflected image of a 100 TW laser incident on a long scale length plasma is measured. The plasma is deliberately preformed on a solid planar target in a controlled way. Multiple highly intense spots are observed inside the original focal spot. These spots could be the experimental evidence for the laser beam relativistic filamentation in the plasma. Three-dimensional particle-in-cell (PIC) simulations for parameters close to the experimental values are performed. The experimental observations and the filamentation dynamics obtained in the PIC simulations are in a good agreement.

Long-scale jetlike x-ray emission was observed in a 100-TW laser-plasma interaction. The jet was well collimated with a divergence of 30--40 mrad and continued from the target surface into underdense regions for a distance over 4 mm in the specular direction of the laser light. A two-dimensional particle-in-cell simulation shows an electron acceleration with the specularly reflected laser light and collimation of the electron stream by a self-generated magnetic field, resulting in the electron jet to the direction of the specularly reflected light.

The fast ignitor scheme for achieving inertial fusion energy precompresses the DT fuel to more than 1000 times the solid state density with nanosecond laser pulses. It then employs a picosecond 10–100-PW laser pulse to deposit with very high efficiency the energy necessary to achieve the ignition temperature of approx. 4 keV. In this way the necessary driver energy for inertial fusion energy reactors is reduced from the megajoule level to the 100-kJ level. In this article, we present results relevant to the development of the fast ignitor scheme that have been achieved in recent years by Australian teams in collaboration with international teams. The topics that are specifically addressed are: (1) forces and relativistic mechanisms of laser interaction with the electrons in the intense picosecond beams; (2) electron and ion emission from the focused beam into the precompressed plasma, including double layer effects and collective stopping power; and (3) the energy of the picosecond beam, which when nearly uniformly deposited into the precompressed DT-fuel can achieve the conditions for high-gain volume ignition. Positive results are derived for the volume ignition scheme from considerations of recent high neutron gain laser fusion experiments.

The 30-TW GEKKO-MII short pulse laser is completed and is used for high field physics studies, including a basic fast ignitor research. The second harmonic (2ω) backscattering shows critical surface recession due to the laser photon pressure. A few hundred protons and deuterons are observed. The 100-TW GEKKO-XII short pulse laser, a petawatt laser module, is constructed to study a feasibility of fast ignition of an imploded target.

High intensity laser propagation in plasmas is one of the key issues in fast ignition scheme of laser fusion energy. We have investigated experimentally and computationally the laser propagation in dense plasmas. The experiment demonstrates plasma channel formation and indicates laser propagation through overdense plamsas with relativistic self-focusing. The channel direction coincides with the laser axis. Two and three-dimensional particle-in-cell simulation reproduces the plasma channel and reveals that the laser propagation is dependent on the laser focus position in plasmas.

The recent high core gains of 29% in laser fusion experiments at the LLE Rochester are evaluated and compared with related earlier measurements where surprisingly the self-similarity model for volume compression provides a common description. This is a proof that the isentropic conditions of stagnation-free compression were mostly fulfilled at the optimized experimental gains, in contrast to highly entropy-producing shock and central spark conditions. Some projections are given of how these results may be generalized to volume ignition for the parameters of the NIF (National Ignition Facility). The proof of stagnation-free volume compression for the best laser fusion gains indicates the advantages of volume ignition, which not only is ‘robust’ and simply follows the natural adiabatic compression, but also is much less sensitive to instabilities and mixing. However, its essential advantage is that it is free from symmetry problems – in contrast to spark ignition, with its spherical detonation front.

The concept of “Fast ignitor” has been proposed several years ago in inertial confinement fusion1. This new approach may require compressed core structure and density already demonstrated and may l...

The 30 TW GEKKO MII short pulse laser (25 J in 0.71 ps at 1 μm) is completed and is used for fast ignitor and particle accelerator research. The photon pressure of the laser at 10 17 –10 18 W/cm 2 pushed the critical and quarter critical density plasmas forward, resulting in the strong red shifts of the second (2 ω 0 ) and three-halves (3 ω 0 /2) harmonic emissions backscattered from CH or CD planes. A few hundred keV proton and deuteron emissions are also observed from CD planes.

Pellet injection and repetitive laser illumination are key technologies for realizing inertial fusion energy. Numerous studies have been conducted on target suppliers, injectors, and tracking systems for flying pellet engagement. Here we for the first time demonstrate the pellet injection, counter laser beams' engagement and neutron generation. Deuterated polystyrene (CD) bead pellets, after free-falling for a distance of 18 cm at 1 Hz, are successfully engaged by two counter laser beams from a diode-pumped, ultra-intense laser HAMA. The laser energy, pulse duration, wavelength, and the intensity are 0.63 J per beam, 104 fs, and 811 nm, 4.7 × 10(18) W/cm(2), respectively. The irradiated pellets produce D(d,n)(3)He-reacted neutrons with a maximum yield of 9.5 × 10(4)/4π sr/shot. Moreover, the laser is found out to bore a straight channel with 10 μm-diameter through the 1-mm-diameter beads. The results indicate potentially useful technologies and findings for the next step in realizing inertial fusion energy.

A series of experiments were conducted using cryogenic deuterium targets to study fundamental physics and implosion dynamics with the GEKKO XII glass laser system [IEEE J. Quantum Electron. QE‐17, 1639 (1981)]. Preheat sources were found to be due to a shock wave and hot electrons. A new method to measure the fuel ρR using proton spectra was employed. Measured in detail were the implosion dynamics of cryogenic deuterium foam with a plastic ablator and a CH shell with a controlled pressure of deuterium gas targets. Under current experimental conditions sources of nonuniformity were discussed in terms of Rayleigh–Taylor instability.

This reports provide an amorphous nanostructuralization technique on the surface modification in Highly Oriented Pyrolytic Graphite (HOPG) by using a femtosecond laser. We showed, for the first time, that the surface of HOPG is changed to the amorphous nanostructuralization graphite by using a femtosecond laser-driven compression technique. Our results also suggest that the HOPG surface is changed until the deeper area from the surface by the laser-driven shock wave. A single shot of a femtosecond laser beam (1.27 ~ 1.33×1014 Wcm~2 in intensity, with 2 mm-diameter, and 110 fs in pulse width) is irradiated under the vacuum ambience onto a 2 mm-thick of HOPG. The calculated impact pressures on a sample was 8.3 ~ 8.7 GPa. Crystal structure in the HOPG were analyzed using a Raman spectroscopy and an X-ray diffraction, those analyzing depth from the surface were 50 nm and 350 μm, respectively.

The HAMA is 1-Hz fast heating fusion driver pumped by a 10 J second-harmonic of diode-pumped Nd:glass laser: KURE-1. We have upgraded HAMA to realize an implosion of spherical shell target by using a remaining fundamental beam from KURE-1. This beam of 6 J/1 Hz is transported to the current counter irradiation system. The resulting beam includes three pulses in sequence: 2.2 J/15 ns and 0.7 J/300 ps for implosion, and 0.5 J/ 190 fs for heating. We estimate the implosion dynamics from 1-D radiation hydrodynamic code (START- 1D). It indicates a possibility of tailored-pulse implosion by optimizing the beam spot sizes of imploding beams on the target surface. This upgrade leads to a demonstration of repetitive implosion and additional heating of a spherical shell target in accordance with a repetition of laser operation and that of a target injection system.

To construct a unified experimental machine CANDY using a kJ DPSSL driver in the fast-ignition scheme, the Laser for Fast Ignition Experiment (LFEX) at Osaka is used, showing that the laser-driven ions heat the preimploded core of a deuterated polystyrene (CD) shell target from 0.8 keV to 2 keV, resulting in 5 x 108 DD neutrons best ever obtained in the scheme. 4-J/10-Hz DPSSL laser HAMA is for the first time applied to the CD shell implosion- core heating experiments in the fast ignition scheme to yield neutrons and also to a continuous target injection, which yields neutrons of 3 x 105 n/4πsr n/shot.

We propose the direct heating of an imploded plasma core by ultra-intense lasers in inertial confinement fusion, to increase the heating coupling efficiency. In this scheme, both fast-electrons and fast-ions heat the plasma core. Experiments using this direct heating scheme has been carried out at GXII and LFEX laser facility at Osaka Univeristy. To model this direct heating scheme, we developed the 1D simulation model and carried out simulations using the experimental conditions. Comparison between results of the simulation and the experimental observations validates the simulation model. We show that even in the unoptimized experimental conditions used in simulations, our calculations show that the maximum temperature, 1.6 keV, of the CD plasma.

We have developed the shadowgraph and interferometer with second-harmonic of heating pulses laser to observe target and plasma in highly-repetitive fusion reaction experiments. In the deuterated polystyrene ((C8D8)n double foil experiment, we confirm implosion plasma and plasma collision. In target injection experiment at a 1 Hz rate, we measure the position of the flying deuterated polystyrene beads at the moment of laser pulse illumination and observe the plasma generation by counter-illumination by 0.63 J, 800 nm, and 104 fs laser pulses.

Pellet injection and repetitive laser illumination are key technologies for realizing inertial fusion energy[1-4]. Neutron generator using lasers also requires a repeating pellet target supplier. Here we present the first demonstration of target injection and neutron generation[5]. We injected more than 1300 spherical deuterated polystyrene(C8D8) bead pellet targets during 23 minutes at 1 Hz(Fig. 1). After the pellet targets fell for a distance of 18 cm, we applied the synchronized laser-diode-pumped ultra-intense laser HAMA. The laser intensity at the focal point is 5 x 1018 W/cm2, which is high enough to generate neutrons. As a result of the irradiation, we produced 2.45-MeV DD neutrons. Figure 2 shows the neutron time-of-flight signals detected by plastic scintillators coupled to photomultipliers. The neutron energy was calculated by the time-of-flight method. The maximum neutron yield was 9.5 x 104/4π sr. The result is a step toward fusion power and also suggests possible industrial neutron sources.

A principle of the laser wakefield particle acceleration has been tested by the Nd : glass laser system with the peak power of 30 TW and the pulse duration of 1 ps. The particle acceleration up to 18 MeV/c has been demonstrated by injecting 1.0 MeV/c electrons emitted from a solid target by an intense laser impact. The corresponding field gradient achieves 1.7 GeV/m.

We have started a new project of inertial fusion driven by all diode-pumped solid-state laser (DPSSL). 105 DD fusion neutron yield from a 500-µm-thick deuterated polystyrene film has preliminarily demonstrated by 10 TW HAMA laser.

This paper reviews the characteristics and recent applications of electron-beam controlled CO2 lasers on the base of the system of the Osaka University. The system has much advantages over TEA lasers. It can provide intense short pulses of as high as 1kJ energy and as short as 1 ns or less width. Many systems are used for the studies of nonlinear interaction with matters, such as a beat-wave accelerator.

The CO2 laser group at the Institute of Laser Engineering, Osaka University is equipped for doing on the laser beat-wave acceleration experiment. By injection-locking with the 9P (22) line in a piezoelectric-controlled CO2 laser cavity, we have obtained a well-balanced double line oscillation of the 9P (22) and 10P (20) lines, that is to say, the shot to shot stability as for the double line balance is more than 90%. The total output is 300 J in 1 ns pulse. The energy and balance between two lines are suited for the beat-wave acceleration.

A direct energy conversion method is proposed for a D-3He inertial confinement fusion reactor. The method utilizes inductive energy recovery through pickup coils in the plasma chamber in which mirror magnetic fields are applied. A method to reduce the problems regarding the handling of ultrahigh voltage inherent in energy recovery of this type is proposed that divides a one-turn pickup coil into a number of pickup segments both axially and azimuthally to reduce the output voltage per pickup segment so that it can be managed by near-term technologies.Analytical results predict that the expanding plasma energy is directly converted to electricity through the recovery circuit using capacitors with an efficiency of >80% when the plasma is assumed to expand cylindrically.

The laser accelerator provides us not only ultra high field, but also extremely short pulse radiation sources, the laser‐produced X‐rays. Using a 1.2 TW table‐top Ti:sap laser, we are pursuing the activities for the industrial application. First we proposed a new injection acceleration scheme using the ultra short beat‐wave accelerator for the economical radiation source. Then we proposed two applications both on the backward see‐through vision of distant objects using the laser X‐rays, and on the X‐ray illumination on Aspergillus awamori spores, which is 100 times effective of the current X‐ray tube cases.