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(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.

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.

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.

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.

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.

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

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. >

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...

Stimulated Raman scattering (SRS) in cannonball targets was experimentally investigated. Above the observed threshold laser intensity, the energy conversion to superhot electrons (E=100–800 keV) shows an increase of five orders of magnitude without saturation. Major differences in observing SRS from cannonball targets and directly driven targets lie in the background electron temperature and the electron plasma density where SRS occurs. A simple model calculation is presented and is compared with the data to infer coronal temperatures. The electron density ranges from 5×1019 to 3×1020 cm−3 and the coronal temperature is 0.2 keV for cannonball targets including cavity targets, while the density ranges from 3×1020 to 6×1020 cm−3 and the temperature is 1 keV for the directly driven target. The generation efficiency of SRS light is strongly correlated with superhot electron generation.