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Magnetic reconnection in laser-produced magnetized plasma is investigated by using optical diagnostics. The magnetic field is generated via Biermann battery effect, and the inversely directed magnetic field lines interact with each other. It is shown by self-emission measurement that two colliding plasmas stagnate on a mid-plane forming two planar dense regions, and that they interact later in time. Laser Thomson scattering spectra are distorted in the direction of the self-generated magnetic field, indicating asymmetric ion velocity distribution and plasma acceleration. In addition, the spectra perpendicular to the magnetic field show different peak intensity, suggesting an electron current formation. These results are interpreted as magnetic field dissipation, reconnection, and outflow acceleration. Two-directional laser Thomson scattering is, as discussed here, a powerful tool for the investigation of microphysics in the reconnection region., 13 pages, 12 figures, Physical Review E, in press

A developing supercritical collisionless shock propagating in a homogeneously magnetized plasma of ambient gas origin having higher uniformity than the previous experiments is formed by using high-power laser experiment. The ambient plasma is not contaminated by the plasma produced in the early time after the laser shot. While the observed developing shock does not have stationary downstream structure, it possesses some characteristics of a magnetized supercritical shock, which are supported by a one-dimensional full particle-in-cell simulation taking the effect of finite time of laser-target interaction into account., 7 pages, 6 fitures

High-power, short-pulse laser-driven fast electrons can rapidly heat and ionize a high-density target before it hydrodynamically expands. The transport of such electrons within a solid target has been studied using two-dimensional (2D) imaging of electron-induced Kα radiation. However, it is currently limited to no or picosecond scale temporal resolutions. Here, we demonstrate femtosecond time-resolved 2D imaging of fast electron transport in a solid copper foil using the SACLA x-ray free electron laser (XFEL). An unfocused collimated x-ray beam produced transmission images with sub-micron and ∼10 fs resolutions. The XFEL beam, tuned to its photon energy slightly above the Cu K-edge, enabled 2D imaging of transmission changes induced by electron isochoric heating. Time-resolved measurements obtained by varying the time delay between the x-ray probe and the optical laser show that the signature of the electron-heated region expands at ∼25% of the speed of light in a picosecond duration. Time-integrated Cu Kα images support the electron energy and propagation distance observed with the transmission imaging. The x-ray near-edge transmission imaging with a tunable XFEL beam could be broadly applicable for imaging isochorically heated targets by laser-driven relativistic electrons, energetic protons, or an intense x-ray beam.

International audience; In this paper, we present the effects of a radiative shock (RS) on the morphology of jet-like objects subjected to hydrodynamic instabilities. To this end, we used an experimental platform developed to create RSs on high energy laser facilities such as LULI2000 and GEKKO XII. Here, we employed modulated targets to initiate Richtmyer–Meshkov and Rayleigh–Taylor instability (RTI) growth in the presence of an RS. The RS is obtained by generating a strong shock in a dense pusher that expands into a low-density xenon gas. With our design, only a limited RTI growth occurs in the absence of radiative effects. A strongly radiative shock has opposite effects on RTI growth. While its deceleration enhances the instability growth, the produced radiations tend to stabilize the interfaces. Our indirect experimental observations suggest a lower instability growth despite the interface deceleration. In addition, the jets, produced during the experiment, are relevant to astrophysical structures such as Herbig–Haro objects or other radiatively cooling jets.

To clarify the property of tritium removal from carbon codeposition by using pulsed-laser induced desorption, hydrogen removal from co-deposits on JT-60 divertor tile using a fourth-harmonic emission (266 nm) of a nano-sec Nd:YAG laser was demonstrated. The threshold laser fluence for ablation was ∼0.3 J/cm 2 , which was slightly higher compared to that of the pico-sec laser irradiation. The energy absorption coefficient for the nano-sec laser, which was obtained by fitting the removal rate by so-called Beer’s law, was larger than the pico-sec laser. Since the time constant of thermal wave propagation into the target is of the order of nano-sec, such differences between nano- and pico-sec lasers could be attributed to thermal effects. The ablation threshold of the deposited layer was lower than that of a pure graphite, which could be attributed to the difference of thermal conductivity between deposited layer and pure graphite. The removal rate of the nano-sec laser was higher than that of pico-sec laser in the fluence range of >∼0.5 J/cm 2 . On the other hand, the production ratio [hydrocarbon species]/[H 2 ] continuously increased with the laser fluence, and no significant ionization of carbon was observed in this fluence range. This indicated that the fluence range in this study was “weak”-ablation range, which was still not sufficient to minimize the hydrocarbon production.

For comparative assessment of tokamak and helical reactors, two base case reactor designs with 1 GW electric power output are introduced; high-field high-beta compact tokamak reactor TR-1 (major radius R = 5.2 m, magnetic field B = 7.1 T) and high-beta helical system HR-1 (R = 12.1 m, B = 4.6 T). Operational boundaries of both reactors are compared by the zero-dimensional energy balance model, which clarifies the difference between the higher temperature operational regime of TR-1 and the lower temperature regime of HR-1. These operational scenarios are reconfirmed by the toroidal transport analysis linkage (TOTAL) code coupling with two-dimensional equilibrium in the TOTAL-T tokamak code and three-dimensional equilibrium in the TOTAL-H helical code. The beta effect on confinement degradation and the impurity radiation effect on energy balance are found to make the ignition difficult in both systems.

(CH4)-C-13 was injected through graphite and tungsten spherical limiters in reproducible TEXTOR discharges. These materials were chosen, as they represent the actual compromise for the plasma facing components in the ITER divertor. C-13 was used in order to distinguish injected and intrinsic carbon in the layer deposited on the limiter surface. Shot-by-shot video recordings show a continuous growth of the deposit near the injection hole. A pronounced difference in the C-13 deposition pattern on the graphite and tungsten limiters was observed. Post-mortem surface analysis showed that the ratios of the locally deposited to the injected amount of carbon are 4% for graphite and 0.3% for tungsten. The margins of the carbon layer deposited on tungsten are significantly steeper in comparison with the graphite limiter case. The large difference in the C-13 deposition efficiency can be explained by direct reflection of carbon from tungsten and the enhanced sputtering of carbon on the tungsten substrate. Nucleation is suggested to be an important mechanism for carbon deposition on tungsten. Monte Carlo impurity transport calculations by the ERO code reproduce reasonably the experimental results for the graphite limiter.

High-density plasma production by helicon waves in a simple torus has been investigated. The measured plasma density np versus external magnetic field B0 peaks at a condition close to the lower-hybrid resonance in H2, D2, and He. Three density regions are observed in the variation of rf power Prf. In the low-density region, helicon waves are not excited and plasmas are produced by an antenna induction field. In the medium- and high-density (H) regions, helicon waves with the m=+1 azimuthal mode are excited and plasmas are produced by the waves. In H2 plasmas, the second-radial mode is dominant over the first-radial mode at Prf>10 kW in the H region. The measured kz−np relation (kz is the wave number parallel to B0) of helicon waves in the H region shows deviation from that of the m=+1 mode derived using the uniform-plasma assumption. The kz−np relation is calculated for various radial-np profiles; parabolic, modified-parabolic, and Gaussian profiles. The difference in the kz−np relation of the m=+1 mode between the uniform- and nonuniform-plasma models is explained by adding a vacuum region between a uniform plasma and the radial boundary.

High-density hydrogen-plasma production in a simple torus using the m=+1 azimuthal mode of helicon waves is investigated. The measured dispersion relation of helicon waves in the high-density region shows deviation from that of the m=+1 mode derived using a uniform-plasma dispersion relation. The dispersion relation is calculated for the parabolic, modified-parabolic density profiles, and for a uniform plasma with a vacuum region.

Properties of high-density nitrogen plasmas with excitation of the m=0 mode helicon wave has been studied for reactive plasma sputter synthesis of carbon nitride films. High-density nitrogen plasmas with densities of 4×1012 cm−3 were obtained in nitrogen at ∼0.1 Pa. Optical emission spectroscopy showed that the line emissions of atomic nitrogen (NI) and atomic-nitrogen ions (NII) were considerably enhanced in the helicon wave-excited high-density plasma, whereas, the spectra measured from the induction-mode (non-wave excitation) low-density plasma were dominated by those of the molecular band emission associated with the first positive system of N2. Carbon nitride films have been deposited on Si (100) substrates by reactive sputtering of carbon target with the helicon wave-excited high-density nitrogen plasmas at ∼0.1 Pa. Compositional characterizations of the CN films were performed using Rutherford backscattering spectrometry (RBS). The RBS analysis showed that the N/C ratio of ∼1.3 was achieved by depositing the CN films at plasma densities as high as 1×1012 cm−3, where the line emissions of atomic nitrogen were significantly higher than the molecular band emissions. Increase in the plasma density and/or the emission-intensity ratio of the atomic nitrogen (NI) to the molecular band in the vicinity of the substrate was found to directly contribute to the N/C composition ratio in the CN films. Structural analysis by Fourier transform infrared spectroscopy (FTIR) showed that the bonds associated with hydrogen impurity could be effectively eliminated by increasing the substrate temperature during film depositions.

Large-area and high-density RF plasmas at 13.56 MHz have been produced in a discharge chamber with 400 mm inner diameter and 200 mm height by inductive coupling of an internal-type double half-loop antenna (320 mm diameter). The present study has been carried out to develop the basic discharge techniques that can be applied to the production of high-density and large-volume plasmas for a variety of plasma-based ion implantation (PBII) processes. The plasma source could be operated stably at RF input powers up to 2.5 kW to attain a plasma density as high as 5×1011 cm−3 at argon pressures of approximately 1 Pa. It has been demonstrated that a high-plasma density can be obtained using the low-inductance internal antenna configuration for effective suppression of the electrostatic coupling. Discharge experiments in nitrogen and hydrogen resulted in a radially uniform plasma production with density as high as 5–9×1010 cm−3.

Large-area high-density RF plasmas at 13.56 MHz have been produced by inductive coupling of an internal-type double half-loop antenna (320 mm diameter), which was immersed in the discharge chamber with 400 mm inner diameter and 200 mm height. The plasma source could be operated stably at RF input power of up to 2.5 kW to attain plasma densities as high as 5×1011 cm−3 at argon pressures around 1 Pa, simultaneously achieving effectively suppressed electrostatic coupling. Azimuthal distribution of the plasma density showed the nonuniformity with m=2 mode, which was found to be controlled by the RF voltage distribution along the antenna and the gas pressure.

Development of high density RF plasma sources at low pressures is described based on the production of inductively-coupled plasmas (ICP) for the application to varieties of physical vapor deposition (PVD) processes. Two types of plasma sources are studied; one is an ICP with a conventional helical antenna for magnetron sputtering assistance and the other is a large-diameter ICP sustained with a low inductance double half-loop antenna. In both systems the RF antenna is located within the vacuum chamber and is terminated to the grounded earth potential via a blocking capacitor. By a simple circuit analysis it was found that the floating antenna configuration effectively suppressed the anomalous rise of the plasma potential, which has been verified experimentally. A large-diameter ICP production with a double half-loop antenna of 320 mm in diameter was successfully employed for reducing the antenna inductance, and full coverage of the antenna with an insulator tubing exhibited a significant effect on the suppression of the electrostatic coupling. Azimuthal distribution of the plasma density in this source showed a non-uniformity with m =2 mode. Dense plasmas with plasma density ranging 10 11 –10 12 cm −3 were sustained in both sources. These types of plasmas are expected to be applicable as a tool for enhanced ionization in the sputtering process and for three-dimensional ion based PVD processes.

The growth and nonlinear evolution of the modified Simon–Hoh instability (MSHI) is observed in a weak electron beam-produced collisionless cylindrical plasma, in which electrons are strongly magnetized and the ions are essentially unmagnetized. The evolution of this instability occurs through a sequence of sideband instabilities, thought to be induced by trapped ions, and a period doubling sequence. Transient study of the MSHI reveals that the growth rate of the MSHI is extremely rapid; of the order the instability frequency.

The contribution of the slow waves (SWs) on high-density plasma production by m=0 helicon waves is investigated in H2, D2, He, N2, Ne, Ar, and Xe plasmas. The density-jump is observed in all the gases used at optimum external magnetic fields B0. The measured plasma density np as a function of B0 peaks at a condition close to the lower-hybrid resonance in H2, D2, He, N2, and Ne, whereas, the measured dispersion relation indicates the excitation of helicon wave. Dispersion relation of electromagnetic waves is solved using dielectric tensor elements of a cold uniform plasma including ion terms, which shows two branches: the SW and fast (helicon) wave. The transition from the ionization by SWs, which are excited in the low-density plasma produced by an antenna induction field, to that by helicon waves has been predicted to explain the mechanism to produce the high-density plasma in the helicon wave discharges.

The production of high-density plasmas with excitation of the m =0 mode helicon wave has been studied for the highly reactive sputter synthesis of carbon nitride films in N 2 and N 2 +Ar mixtures in the pressure range of ~0.1 Pa. High-density plasmas of 10 12 –10 13 cm −3 were produced even in pure N 2 by using a helical antenna with an azimuthal mode number of m =0. The helicon-wave-excited plasmas have been investigated by wave-magnetic-field measurements and optical emission spectroscopy. The plasma density achieved in 0.26 Pa nitrogen was 4×10 12 cm −3 at a radio frequency (RF) power of ∼3 kW and a static magnetic field strength of ∼1000 Gauss. The wave-magnetic-field measurements confirmed excitation of the m =0 mode helicon wave to propagate in the plasmas at the onset of attaining the high-density mode. Significant enhancement of line emissions of atomic nitrogen (N I) and nitrogen ions (N II) was observed in the helicon-wave-excited plasma, whereas the optical emission spectra in the induction mode were dominated by those from the molecular bands of nitrogen. Carbon nitride films have been deposited on a Si(100) substrate by using reactive sputtering of a cylindrical carbon target with the wave-excited high-density plasmas in N 2 and N 2 +Ar mixtures at around 0.1 Pa. Compositional and structural characterization of the CN films was performed by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS), showing that the N/C ratio in the CN films could be controlled up to 1.3. Chemical and structural analysis by XPS has been performed. The XPS analysis showed the existence of peaks indicating a C=C bond and two C=N bonds where nitrogen is bonded to carbon atoms in sp 2 - and sp 3 -hybridized states. Nanoindentation measurements showed that hardness values as high as ∼20 GPa were attained at a substrate bias of −200 V.

Studies directed towards the reduction of particle and heat fluxes to plasma facing components by the application of ponderomotive forces generated by radio frequency (RF) are being conducted in TEXTOR. A modified poloidal limiter is used as an antenna with up to 3 kW of RF power; the data obtained show that the plasma is repelled by the RF ponderomotive potential. The density is reduced by a factor of 2–4 and the radial decay length is substantially altered. The density near the limiter decays exponentially with RF power. The electron temperature profile changes, with the decay length becoming longer (almost flat) during the RF. The temperature in the scrape off layer (SOL) increases and its increase is roughly proportional to the RF power until it saturates, suggesting that the heating efficiency drops with power, and that improved performance is to be expected at higher powers.

The axial profile of the axial component of the wave magnetic field has been measured for m = 0 helicon waves. A dip in is observed at cm from the antenna, and is explained as a result of the beat between the fundamental and the second-order radial modes of the m = 0 helicon wave. The measured imaginary part of , which consists only of the wave field, is compared with that of the calculated wave field using the theory of the uniform plasma case. It is found that % of the amplitude arises from the second-order mode and the axial damping length of the fundamental mode .

Thermonuclear ignition and subsequent burn are key physics for achieving laser fusion. In fast ignition, a highly compressed fusion fuel generated with multiple ns‐laser beams is rapidly heated with a large energy, ps‐laser pulse in prior to core disassembly. This scheme has a high potential to achieve ignition and burn since driver energy required for high fusion gain is predicted to be about one tenth of that needed for the central ignition scheme. In Japan, Fast Ignition Realization Experiment (FIREX) project has been started to clarify the physics of energy transport and deposition in the core plasma and to demonstrate fuel temperature of above 5 keV. After the success, FIREX‐I will be followed by the second phase of the project (FIREX‐II) to demonstrate ignition and burn. LFEX laser, designed to deliver a laser pulse of 10 kJ in 10 ps, are operational and the first phase of FIREX experiments has been stated. A new target is proposed to attain dense compression of fuel and improve laser‐core coupling efficiency by adopting double‐cone structure, a low‐density inner liner, low‐Z outer coating, and Br‐doped fuel shell. In this paper, present status and near term prospects of the FIREX‐I project will be reported together with activities on target designing, laser development, and plasma diagnostics.

We aim to study the effect of the long‐range correlation among ions on their statistical characteristics using ion clouds confined in a linear rf ion trap. It is important to keep the ion cloud in one dimension, where the influence of the rf heating is negligible, for the detailed research on the effect of the Coulomb interaction on the statistical characteristics of the ion cloud. In this paper, the method of the generation of an ideal ion string is proposed. We also briefly report the performances of our experimental equipment and the preliminary results of generation of ideal 1D ion cloud.

Pressure, density, and temperature data for H2O were obtained up to 260 GPa by using laser-driven shock compression technique. The shock compression technique combined with the diamond anvil cell was used to assess the equation of state models for the P-ρ-T conditions for both the principal Hugoniot and the off-Hugoniot states. The contrast between the models allowed for a clear assessment of the equation of state models. Our P-ρ-T data totally agree with those of the model based on quantum molecular dynamics calculations. These facts indicate that this model is adopted as the standard for modeling interior structures of Neptune, Uranus, and exoplanets in the liquid phase in the multi-Mbar range.

Antenna coupling has been controlled in high-density plasma production by m=0 helicon waves using multiple-loop antennas and varying the phase and the distance between antennas. When two single-loop antennas are connected in series with the phase between the two being zero, threshold power for the density jump Pth is reduced by a factor of 2–3 compared with that of the one-turn loop antenna. This reduction in Pth is caused by the increase in antenna coupling at the lower plasma density. The observed differences in antenna coupling among different antennas have been examined by using a two-dimensional wave code.

The characteristics of the high density plasma production by the m = 0 azimuthal mode helicon wave is investigated. By varying the power of the applied radio frequency Prf two discharge modes exist; one is the low density mode (plasma density np

This paper presents simple algorithm for solving the optimal control problems of discrete-time systems with constraints on control. In this algorithm, monotonous reduction of cost values at each iteration is guaranteed. It is proved that the converged control satisfies the Pontryagin type necessary conditions for optimality under some conditions. >

A simple model that considers the flexibility of constrained manipulators by introducing a set of equivalent springs is proposed. On the basis of the model, the authors derive a controller, which compensates the vibrations of the contact force. For measuring the vibrations and the contact force, accelerometers and a force sensor are used. Output signals of the sensors are fed back to the driving motors for controlling the position of the end-effector and the contact force. Experimental results are shown.

Although DSFB control with constant feedback gain always guarantees closed loop stability, the control performance may not be so satisfactory due to, for instance, robot arm's tip load variations. In this paper, the authors present a simple gain adaptive method to overcome this difficulty. The closed loop stability of gain adaptive DSFB control is proved theoretically, and the effectiveness of the proposed control method is demonstrated by a series of experiments. >

The peak power of 30 TW and the pulse width of 1 ps produced by the Nd:glass laser system is capable of creating a highly-ionized plasma of a moderate density gas on an ultrafast time scale and generating a large amplitude plasma wave with an accelerating gradient of the order of GeV/m. We are going to demonstrate particle acceleration, injecting electrons of a few MeV emitted from a solid target by intense laser irradiation. >

In this paper, a method is proposed whereby both contact force exerted by a flexible manipulator, and position of the end-effector while in contact with a surface are controlled. The authors approximate elastic deformations by means of B-spline functions and derive dynamic equations of joint angles, vibrations of the flexible links, and constraint forces. A controller for the hybrid position/force control of the flexible manipulator is designed on the basis of the singular perturbation method. Experimental results confirm that the controller performs remarkably well. >

A method is proposed whereby both the contact force exerted by a flexible manipulator and the position of the end-effector while in contact with a surface are controlled. The authors approximate elastic deformations by means of B-spline functions and derive dynamic equations of joint angles. A controller for the hybrid position/force control of the flexible manipulator is designed on the basis of the singular perturbation method. >

Laser shock compression experiments on precompressed samples offer the possibility to explore extreme material states unreachable by static or single-shock compression techniques alone. We have found significant increases in static compression pressure in a wide-opening and thin diamond precompression cell. This suggests that the precompression target is adaptable to advanced coupling techniques with laser-driven dynamic compression methods. The novel coupling techniques proposed give the potential to access outstanding material states required in planetary and condensed-matter physics.

Coupling laser-shock and static-compression techniques allows to generate material conditions unreachable by either single-shock or static technique alone. Static compression experiments on water were performed using a precompression cell for laser-driven shock experiments. The pressure on static compression in this work was reproductively 1.3 – 2.3 times higher than in previous works and theoretical predictions. We have also performed static compression experiments using a new anvil material (Gd3Ga5O12) to apply the cell to reflected shock compression. By coupling laser-driven reflected shock compression with precompression technique, it is possible to generate higher pressure and lower temperature range.

The modified Simon-Hoh instability is observed in a collisionless cylindrical plasma, produced by a weak electron beam, in which electrons are strongly magnetized and the ions are essentially unmagnetized. The nonlinear evolution of this instability occurs through a sequence of sideband instabilities, thought to be induced by trapped ions, and can lead to a chaotic state.

A multiantenna rf ion source is studied. The new antenna system is developed to reduce the rf voltage on the antenna compared to that of the conventional loop antenna, which can reduce high voltage rf breakdown on antennas. The antenna was installed in a 1/6 scale ion source for the neutral beam injector (NBI) (H−) used in large helical devices. The characteristics of the ion density current of the plasma produced by using the segmented antennas were studied. A dense plasma with ion saturation current density of 92 mA/cm2 was generated at 45 kW of rf power at 9 MHz for the two-antenna system. At around 10 kW of rf power the plasma density jumped and became a high density mode. The threshold power for the density jump seems to be shifted by the antenna segments and the rf frequency. The current density of the positive ion beam with a small accelerator voltage is 26 mA/cm2 for 10.3 keV of extraction energy, 45 kW of rf power, and 0.16 Pa of plasma source pressure of hydrogen. This multiantenna rf source cou...