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To sustain plasmas with higher parameters and with longer pulse duration in LHD, ECH system has been upgraded by introducing newly developed 77 GHz gyrotrons. The designed output power and operation duration time are over 1 MW for several seconds and 0.3 MW for continuous operation, respectively. Owing to the upgrade of gyrotrons and improved power supply operation procedure, total injection power of EC-waves to LHD increased up to 3.7 MW at the last LHD experimental campaign in 2010. Application of the high-power 77 GHz EC-waves of 3.4 MW as focused beams to the center of plasma with low line-average electron density of ∼0.2×10 19m -3 causes highly steep electron temperature profile and the central electron temperature reached up to 20 keV, which highly exceeds the former record of 15 keV. At higher density region of 1×10 19m -3, central electron temperature reached 8.6 keV. Additional electron Bernstein wave heatings, O-X-B and slow X-B heatings, using a 77 GHz ECH system caused clear increase in plasma stored energy even for the high-density plasmas over plasma cutoff (>7. 35×10 19m -3) sustained with NBI. For the O-X-B scenario, the 77 GHz EC-wave was obliquely injected from low-field side in O-mode polarization, aiming at the point where high mode-conversion efficiency was expected. For realizing slow X-B scenario, new inner-vessel mirrors were installed in LHD just close to a helical coil, that is, at the high-field side (HFS) region. Using the inner-vessel mirror, X-mode waves were injected from HFS, showing evident increase in plasma stored energy. Oblique injection of long-pulse 0.77 MW/8 s 77 GHz wave with various N ∥ clearly demonstrated ECCD in LHD. The EC-driven current changes its direction with the sign of N ∥, and the highest EC-driven current reached up to 42 kA. © 2011 American Institute of Physics.

Electron Cyclotron Resonance Heating (ECRH) has contributed to the achievement of high performance plasma production, high electron temperature plasmas and sustainment of steady-state plasmas in the Large Helical Device (LHD). Our immediate targets of upgrading the ECRH system are 5 MW several seconds and 1 MW longer than one hour power injection into LHD. The improvement will greatly extend the plasma parameter regime. For that purpose, we have been promoting the development and installation of 77 GHz/1-1.5 MW/several seconds and 0.3 MW/CW gyrotrons in collaboration with University of Tsukuba. The transmission lines are re-examined and improved for high and CW power transmission. In the recent experimental campaign, two 77 GHz gyrotrons were operated. One more gyrotron, which was designed for 1.5 MW/2 s output, was constructed and is tested. We have been promoting to improve total ECRH efficiency for efficient gyrotron-power use and efficient plasma heating, e.g. a new waveguide alignment method and mode-content analysis and the feedback control of the injection polarization. In the last experimental campaign, the 77 GHz gyrotrons were used in combination with the existing 84 GHz range and 168 GHz gyrotrons. Multi-frequency ECRH system is more flexible in plasma heating experiments and diagnostics. A lot of experiments have been performed in relation to high electron temperature plasmas by realization of the core electron-root confinement (CERC), electron cyclotron current drive (ECCD), Electron Bernstein Wave heating, and steady-state plasma sustainment. Some of the experimental results are briefly described. © 2009 American Institute of Physics.

Trials of steady-state operation (SSO) in the Large Helical Device (LHD) were started when a continuous wave (cw) gyrotron with the output power up to 0.2 MW was introduced to the electron cyclotro...

The electron cyclotron resonance heating (ECRH) system on the Large Helical Device (LHD) has been in stable operation for ∼11 yr in numerous plasma experiments. During this time, many upgrades to the system have been made, such as reinforcement of the gyrotron tubes, modification of the power supply depending on gyrotron type, and increase in the number of transmission lines and antennas. These efforts allow the stable injection of millimeter-wave power in excess of 2 MW. In parallel, various transmission components were evaluated, and antenna performance was confirmed at a high power level. The coupling efficiency of the millimeter wave from the gyrotron to the transmission line and the transmission efficiency through the waveguide were further improved in recent years. The feedback control of the wave polarization has also been tried to maximize the efficiency of wave absorption. The gyrotron oscillation frequency was reconsidered in order to extend the flexibility of the magnetic configuration in plasma experiments. The development of 77-GHz gyrotrons with the output of 1 MW per few seconds in a single tube is currently taking place in collaboration with the University of Tsukuba. Two such gyrotron tubes already have been installed and were used for plasma experiments recently. An ECRH system with a capability of the steady operation is required, because the LHD can continuously generate confinement magnetic fields using superconducting magnets. Not only the gyrotron but also the transmission system and components must withstand continuous power operation. Further acceleration of both the power reinforcement and a steady-state capability will allow the sustainment of high-performance plasmas.

A 77-GHz, 1-MW gyrotron is being newly installed in the Large Helical Device not only to enhance the total heating power but also to increase the possibility of controlling the local plasma parameters. Our progress in installing the new gyrotron and evaluating its properties is discussed. We have already finished the installation of the peripheral components, including the transmission line, and conducted a test at 1 MW for a short pulse. Our plan is to operate this gyrotron at a power of up to 1MW for 5 s. The conditioning of the gyrotron has been smoothly conducted, and a gyrotron output power up to 810 kWfor 3.6 s has been achieved so far. The total injected power of electron cyclotron resonance heating to the plasma reached a value of ∼2.5 MW.

The configuration of and methods for the Electron Cyclotron Resonance Heating (ECRH) control system in the Large Helical Device (LHD) are discussed. The ECRH system is routinely used for high electron temperature plasma production and sustainment in the LHD and must be remotely operated reliably and stably. The ECRH system consists of several elements that require reliable control and monitoring, including gyrotrons, high voltage power supplies, millimeter wave transmission systems, and antenna systems.

A low-power test system using a vector network analyzer is constructed to evaluate the performance of phase correcting mirrors in a matching optics unit (MOU). The MOU is used in order to facilitate the good coupling of a millimeter wave beam from a gyrotron into corrugated waveguides. The newly developed diagnostic system allows us to make measurements not only of intensity-, but also of phase-profiles of millimeter wave beams and opens a new range of possibilities for designing and testing high-precision quasi-optical systems. Low-power tests are carried out to evaluate the performance of the newly designed MOU by reversely injecting a Gaussian beam from the output port of the MOU. The output beam from the input port of the MOU is measured with the analyzer. In this inverse process, the injected Gaussian beam should be converted to the real beam pattern radiated from the gyrotron. Using correlation analysis, the measured- and calculated-electric fields are compared in their amplitude- and phase-profiles. Good agreement between the measurement and the calculation is obtained. Therefore, it is judged that the phase-correcting mirrors in the MOU will work correctly in upcoming high-power tests.

This paper reports on the results of an experimental investigation into electron cyclotron resonance heating (ECRH) using the fundamental O-mode in the large helical device (LHD). The aim of the experiment is to understand the mechanism of the selective excitation of the O-mode EC wave and, thereby, optimize the performance of the ECRH. The polarization angle and the ellipticity of the electric field of the incident high power millimetre waves were varied in the experiment using a pair of grating polarizers. The responses of the plasma stored energy and electron temperature were measured to evaluate the effects. The optimum values of the polarization angle and the ellipticity for the ECRH were identified experimentally. A simple model of power branching between the O- and X-modes is introduced in order to interpret the observed experimental results. Specific to the ECRH in the LHD configuration, the effect of magnetic shear in the plasma peripheral region is considered.

The potential of continuous plasma sustainment of Large Helical Device (LHD) was successfully demonstrated by a one hour discharge with 110 kW electron cyclotron heating (ECH) power. The ECH power of frequency 84 GHz generated by a continuous-work (CW) gyrotron is transmitted through an evacuated waveguide transmission line and injected to the LHD vacuum vessel using waveguide antenna. The plasma density was kept at about 1.5 × 1018/m3 and the electron temperature at the plasma center over 1 keV. Due to the low injection power the density was not so high but the plasma was quite stable. The power injection was terminated manually at 3900 seconds from the limitation of the setting of data acquisition, not for any troubles on devices.

Doped LaGaO 3 oxide is considered to be a promising candidate for an electrolyte in intermediate temperature operating solid oxide fuel cell. Doped LaGaO 3 films, with the composition La 1− x Sr x Ga 1− y Mg y O 3−( x + y )/2 was prepared by the pulsed laser deposition technique. The dynamics of the plasma plume during the film deposition was investigated. The estimated velocity of the plume head was in the range of (0.5–1.5)×10 4 m/s depending on ambient pressures. The films deposited on the NiO substrate consisted of many particles and crystalline structure of LaGaO 3 was obtained for post annealed films at 1000 °C for 6 h. A slight difference in stoichiometry between the target and the film was found by secondary ion mass spectroscopy.

We have developed and constructed an ECH system for the large helical device (LHD). The ECH system consists of 0.5 MW, 84 GHz range and 168 GHz gyrotrons, high voltage power supplies, long distance transmission lines, and in-vessel quasi-optical antennas. It has been improved step by step. At the third campaign of LHD experiments, three 84 GHz range (two 82.6 GHz and one 84 GHz) and three 168 GHz gyrotrons are operated and ECH power can be injected from four antennas vertically and two horizontally. This complicated system is remotely controlled and monitored by fully GUI (Graphical User Interface) control panels realized on PC via TCP (transmission control protocol) communication. Over 10 000 shots of gyrotron power have been injected steadily into the LHD during the experimental campaigns on this system. One line of the system (84 GHz line) is specially prepared for the experiments of steady state plasma production. Using this line, plasma sustainment for 2 min was successfully achieved by only ECH power. Injected ECH power was 50 kW with 95% duty factor. The electron density and temperature of the sustained plasma are measured to be 0.3–0.5×1018 m−3 and ∼650 eV. Ion temperature measured by Doppler broadening of the impurity radiation line was kept constant at ∼300 eV during RF injection.

A large helical device (LHD) experiment began at the end of March 1998. Fundamental and second harmonic electron cyclotron heating (ECH) are used as a plasma production and heating method with six gyrotrons whose frequencies are 82.6/84 and 168 GHz, respectively. Up to 0.9 MW power has been injected in LHD with long distance corrugated waveguide transmission systems. The maximum pulse width is achieved to 3.0 s/240 kW for the LHD experiments. Six antenna systems have been prepared at the horizontally and vertically elongated poloidal sections. The maximum stored energy using all six gyrotrons is 70 kJ at the averaged density of n e = 4 × 10 18 m -3 . The maximum central electron temperature T e0 = 3.5 keV is achieved at n e = 3 × 10 18 m -3 . The magnetic field structure in heliotron type devices like LHD, notably near the coil, is complicated. For this oblique injection, a wave is launched from the antenna, and then crosses the plasma in the complex field structure near the coil. The polarization ellipse of the wave is changed along the ray-path. The wave propagation in heliotron type devices has been analyzed in an ideal case that the magnetic field component along the propagation direction can be neglected. Even for perpendicular injection with our antenna systems, the field component along the propagation direction is not so small. Another treatment of the wave-propagation is introduced. Some calculations for the heating scenario with this treatment are shown.

Transmission and reflection coefficients of hybrid modes in the sliding waveguide are discussed on the basis of mode matching method and multi-mode network theory. It is confirmed that the decrease in power of < 0.2% at 84 GHz is obtained for 2 cm in gap of the sliding waveguide which is composed of the corrugated waveguide with 88.9 mm diam. and the smooth-wall waveguide with 110 mm diam. At the sliding length near multi-half-wavelength in vacuum, transmission and reflection powers in the sliding waveguide change slightly, because the very small amount of standing wave in high higher-mode is produced resonantly in the gap.

The initial experiments on the Large Helical Device (LHD) have extended confinement studies on currentless plasmas to a large scale (R = 3.9 m, a = 0.6 m). Heating by NBI of 3 MW produced plasmas with a fusion triple product of 8 × 1018m-3keVs at a magnetic field strength of 1.5 T. An electron temperature of 1.5 keV and an ion temperature of 1.1 keV were achieved simultaneously at a line averaged electron density of 1.5 × 1019 m-3. The maximum stored energy reached 0.22 MJ with neither unexpected confinement deterioration nor visible MHD instabilities, which corresponds to β = 0.7%. Energy confinement times reached a maximum of 0.17 s. A favourable dependence of energy confinement time on density remains in the present power density (~40 kW/m3) and electron density (3 × 1019 m-3) regimes, unlike the L mode in tokamaks. Although power degradation and significant density dependence are similar to the conditions on existing medium sized helical devices, the absolute value is enhanced by up to about 50% from the International Stellarator Scaling 95. Temperatures of both electrons and ions as high as 200 eV were observed at the outermost flux surface, which indicates a qualitative jump in performance compared with that of helical devices to date. Spontaneously generated toroidal currents indicate agreement with the physical picture of neoclassical bootstrap currents. Change of magnetic configuration due to the finite β effect was well described by 3-D MHD equilibrium analysis. A density pump-out phenomenon was observed in hydrogen discharges, which was mitigated in helium discharges with high recycling.

The Large Helical Device (LHD) has successfully started running plasma confinement experiments after a long construction period of eight years. During the construction and machine commissioning phases, a variety of milestones were attained in fusion engineering which successfully led to the first operation, and the first plasma was ignited on 31 March 1998. Two experimental campaigns were carried out in 1998. In the first campaign, the magnetic flux mapping clearly demonstrated a nested structure of magnetic surfaces. The first plasma experiments were conducted with second harmonic 84 and 82.6 GHz ECH at a heating power input of 0.35 MW. The magnetic field was set at 1.5 T in these campaigns so as to accumulate operational experience with the superconducting coils. In the second campaign, auxiliary heating with NBI at 3 MW has been carried out. Averaged electron densities of up to 6 × 1019m-3, central temperatures ranging from 1.4 to 1.5 keV and stored energies of up to 0.22 MJ have been attained despite the fact that the impurity level has not yet been minimized. The obtained scaling of energy confinement time has been found to be consistent with the ISS95 scaling law with some enhancement.

The nickel(II) complexes, [(tpa)NiII(μ-OH)2NiII(tpa)](ClO4)2 (tpa = tris(2-pyridylmethyl)amine) (2), [NiII(CH3CN)(tpa)(H2O)](ClO4)2 (3) have been prepared and fully characterized. X-Ray crystallography of complex 2 and its methanol adduct, [(tpa)NiII(μ-OH)2NiII(tpa)](ClO4)2·2MeOH ((2)·2MeOH) revealed a molecular structure containing two Ni centers bridged by two OH ligands. The Ni–O distances in 2·2MeOH are longer than those in 2. The MeCN ligand in complex 3 is replaced by EtCN to give [NiII(EtCN)(tpa)(H2O)](ClO4)2 (4), which was characterized by X-ray crystallography. The kinetic study of p-NPA (p-nitrophenyl acetate, 0.1, 0.5, 1 mM) hydrolysis by complex 2 (20, 10, 6 mM) was performed in the presence of ethanol (100 mM) in MeCN solution (1 M = 1 mol dm−3). By following the 400 nm absorption derived from p-nitrophenolate ion, we obtained the second-order kinetics; first-order in [2] and first-order in [p-NPA]. Additon of ethanol resulted in enhancement of the second-order rate constant (from 1.6 × 10−3 ...

This paper presents an experiment in which the phase- and amplitude-flattened output of a 168 GHz gyrotron was converted into the HE/sub 11/ mode, the basic transmitting mode in corrugated waveguides, by means of an external matching box (MBOX) comprising two curved-surface mirrors. In estimating the coupling efficiency between the gyrotron output wave and the HE/sub 11/ mode, an improved method was proposed in which the reconstructed phase of the gyrotron output wave at four distances are averaged. From the phase reconstruction with averaging, it was found that 76% of the gyrotron output coupled into the HE/sub 11/ mode in a corrugated waveguide, while a coupling efficiency of 85% was calculated for an ideal gyrotron output. A detailed discussion on the MBOX performance as well as the accuracy of phase reconstruction shows that this low coupling efficiency is due to the nonideality of the actual gyrotron output and that designing the MBOX mirrors based on the actual measurement at the gyrotron window can improve the coupling efficiency.

In Large Helical Device, a power transmission line consists of corrugated waveguides with inner diameter of 88.9 mm for electron cyclotron resonance heating is evacuated in order to transmit higher power by reducing a possibility of electrical breakdown in the line. Some characteristics of such transmission lines, vacuum pumping system and comparison of pressure distribution simulated and gauged along the transmission line are described. An effect of vacuum pumping for higher power transmission is demonstrated.

Silicon nitride composite as a candidate of a window material for high power CW (Continuous Wave) millimeter-waves was high power tested especially with a surface cooling by impinging gas nitrogen jets on the single-disk surface. Gas-cooling dramatically suppressed the temperature of the window disk even with gas flow rate of around 100 l/min. With gas cooling of 465l/min., 130kW CW power of HE11 mode could be transmitted through the silicon nitride window with a diameter of 88.9mm. The peak window temperature was completely saturated on 123.6 °C. Without gas-cooling it did not saturate and reached 323 °C during 30 seconds pulse. A possibility of 1MW CW single disk Brewster windows with a forced gas-cooling is discussed, resulting in convinced prospects of the windows with realistic size and thickness.

The mode-conversion loss in the matching between the gaussian beam emanated from the gyrotron and the hybrid mode in the circular corrugated waveguide with the diameter of 2a is discussed. By numerical calculation, it is found that the loss considerably increases and optimum waist sizew 0 changes when TEM00 mode with the wavelength λ is injected with offset or tilt. By fitting numerical data to the polynomial function, it becomes evident that the scaling formulas of the losses for the off-axis shiftr d and for the tilt angle θ are derived to be 2.3(r d /a)2 – 2.2(r d /a)4 and 3.9(aα/λ)2 – 5.6(aθ/λ)4 for fixedw 0/a=0.643, respectively. To keep the mode-conversion loss ≤1% for the frequency of 168 GHz and 2a=88.9 mm, tilting angle and offset should be less than 0.1 degrees and 2.9 mm, respectively.

An electron cyclotron heating (ECH) system for the compact helical system using two types of high power gyrotron as a power source is designed. In order to utilize fully the advantage of the ECH, the antenna system is designed so as to inject the microwave power as an elliptic gaussian beam, which allows well-defined high power local heating. This antenna and associated transmission system from gyrotron are designed with the quasi-optical concept. This design concept and the results of the cold test for the transmission and antenna system are described. The resultant beam parameter of the cold test for the antenna system shows fairly good agreement with the designed value, which indicates the validity of this design concept. The power transmission efficiency of about 90% was estimated from the measured power at both ends.

One megawatt CW (steady state operation) gyrotrons have been developed. The first gyrotron was the cavity mode output tube which demonstrated the one megawatt capability. The second tube is made by modifying the output mode to a Gaussian one by a built-in high efficiency quasi-optical mode converter. The designs, cold tests and preliminary test results are described.

The generation of an elliptical gaussian beam for an antenna for the large helical device is discussed. Numerical and experimental results on a square corrugated waveguide and parallel corrugated plates and its combination are described. It is shown that the parallel corrugated plates provide a good performance for the elliptical gaussian beam.

The phenomenon of density pump-out or the degradation of particle confinement is observed for plasmas with electron cyclotron heating (ECH) in the compact helical system. It is confirmed that the enhancement of the particle flux with ECH is triggered by the production of electrons accelerated perpendicularly to the magnetic field with ECH.

Experimental measurements by wavepacket reflectometry are carried out to verify the low transmission loss of hybrid mode on HE11 in the corrugated waveguide with 88.9 mm in diameter. The HE11 mode is injected into the 62-m straight circular corrugated waveguide and the beat between the HE11 and HE21 (including degenerated TE01 and TM02) modes is observed. The loss is too small to measure and inferred to be less than 2 db/km. The result shows that the use of HE11 mode for electron cyclotron heating system is suitable.

Characteristics of the H-mode transition observed in CHS are described. The transition is achieved with modification of the rotational transform profile by inducing a small ohmic heating current. The transition is often initiated by a sawtooth crash caused by a coherent mode with the poloidal mode number m=2 and toroidal one n=1.

The bootstrap current and electron thermal conductivity have been investigated in ECRH plasmas on the CHS heliotron/torsatron. The neoclassical transport coefficients have been externally controlled over a wide range by changing the ellipticity of the plasma cross-section. While local thermal conductivity, as well as global confinement, have shown inconsistency with the neoclassical predictions, the observed toroidal net current has been successfully explained by considering the three dimensional geometry with the available neoclassical theory. The present experimental results indicate that the transport parallel to the magnetic field lines (bootstrap current) is likely to be neoclassical but that the perpendicular transport (thermal conductivity) is anomalous, which is common in current less plasmas as well as tokamaks

Millimeter-wave components were re-examined for high power (Mega-Watt) and steady- state (greater than one hour) operation. Some millimeter-wave components, including waveguide joints, vacuum pumping sections, power monitors, sliding waveguides, and injection windows, have been improved for high power CW (Continuous Waves) transmission. To improve transmission efficiency, information about the wave phase and mode content of high power millimeter-waves propagating in corrugated waveguides, which are difficult to measure directly, were obtained by a newly developed method based on retrieved phase information. To optimize the plasma heating efficiency, a proof-of-principle study of the injection polarization feedback control was performed in the low power test stand.

Three Mega-Watt 77GHz gyrotrons were developed for an ECRH system in LHD. Their operation could be highly optimized by means of two-step rise of an anode voltage. Output power of 1.78MW with 37.9% efficiency were obtained in the 3rd gyrotron. The system improvement has been promoted including the development of a mmw-beam position and profile monitor. © 2011 IEEE.

In LHD, an ECH system for fusion-relevant plasma heating has been greatly progressed with the development of megawatt gyrotrons. Net power of 3.7 MW could be injected into LHD. For stable operation, a new position and profile monitor of the mmw-beams in evacuated transmission lines is developed. © 2010 IEEE.

A self-consistent analytical solution for net erosion of a divertor plate which is set perpendicular to magnetic field lines is presented. The primary flux profile of hydrogen and impurities except redepositing particles is externally given as well as the return ratio of sputtered atoms to the plate. In the direction along the divertor trace, all conditions are uniform. The ionization mean free path is assumed constant to simplify equations. The analytical solution is compared with net erosion experiments carried out in compact helical system (CHS) by exposing a graphite target to a neutral beam heated plasma column introduced perpendicularly to the target along the magnetic field lines through a 2 cm slit opened on a graphite limiter. After exposure to 98 discharges, the target surface is analyzed with Rutherford backscattering method. Deposition profiles of Ti and O impurities are very well explained with the analytical predictions.

This paper reviews recent experimental results from compact helical system (CHS), a heliotron/torsatron type device with a low aspect ratio of 5. Transport phenomena are discussed through analyses of MHD equilibrium, thermal/particle diffusivity and viscosity. It is seen that transport is dominated by anomalous processes which are thought to be due to electrostatic fluctuations. On the basis of these results, optimization of confinement by shifting the vacuum magnetic axis is briefly discussed.

The MHD equilibrium properties of neutral beam heated plasmas have been experimentally investigated in the Compact Helical System (CHS)-a low aspect ratio (Ap ~ 5) heliotron/torsatron. This configuration is characterized by a strong breaking of helical symmetry. The radial profiles measured by various diagnostics have shown a significant Shafranov shift due to the plasma pressure. The deviation of the magnetic axis from is vacuum position has become as large as 50% of the minor radius. When the three-dimensional equilibrium code VMEC is used to reconstruct the equilibrium from the experimental data, the result is in good agreement with the experimentally observed Shafranov shift as well as with the diamagnetic pressure in plasmas with β ≤ 1.2% and β0 ≤ 3.3%. This beta values corresponds to half of the conventional equilibrium β limit defined by the Shafranov shift reaching a value of half of the minor radius. Although tangential neutral beam injection causes pressure anisotropies, p||/p⊥ ≤ 3, the description of the equilibrium assuming isotropic pressure is consistent with the experiment

A new method is proposed to analyze mode contents of high power electromagnetic waves that are propagating through corrugated waveguides in the electron cyclotron resonance heating (ECH) system for nuclear fusion devices. The method was applied to a 168 GHz transmission line of the ECH system in Large Helical Device (LHD) to evaluate the waveguide misalignment. Mode contents of the propagating wave could be well obtained, and the wave field in the waveguide was reconstructed by using the information of each mode.

A movable graphite limiter with an internal heater has been installed in the heliotron/torsatron type compact helical system (CHS). Comparing discharges with and without the limiter the origin of major impurities and the role of the limiter are discussed. Infrared TV measurements reveal that there are two hot spots on the limiter due to heat loading and their temperatures depend on the electron density and/or the magnetic field direction. Limiter temperature dependence of measured CH/Hγ, CI, CII, OII, CH+3, OV and total radiation loss is compared. From these experiments it is concluded that CH4 molecules produced chemically on the limiter are presumed to recycle rapidly near the limiter and both carbon and oxygen impurities result probably from CO produced chemically on the limiter with oxygen which is predominant in CHS and originates mostly from the first wall. At surface temperatures above 900 ° C the limiter effect on impurities is observable in the main plasma.

In order to reduce oxygen impurity and hydrogen recycling, ECR discharge cleaning with hydrogen, glow discharge with helium, and titanium gettering have been applied. The ECR discharge cleaning was found to be effective in reducing oxygen impurities in ECRH discharges. However, it was not sufficiently effective to give a wide operational density range in NBI heated discharges. Titanium gettering is essential for this purpose, and controllable discharges have been achieved in the density range 1–10 × 1019 m−3, with discharge length more than 850 ms with the aid of titanium gettering. Both helium-glow discharge and Ti gettering are useful to control hydrogen recycling even with a stainless steel wall.

The Compact Helical System was designed for research on transport in a low-aspect-ratio helical system. The machine parameters were chosen on the basis of a physics optimization study. Considerable...

We developed 8 times 8 beam-deflecting optical switch with a switching speed within one microsecond utilizing electro-optic effect of PLZT. A newly-developed radial optical path design and putting-in packaging structure with a monolithic PLC platform were applied.

There are several important roles for the electron cyclotron resonance heating (ECRH) methods in helical-type plasma experimental devices. One is to produce high-temperature and high-density current-free plasmas. Another is additional heating of electrons and resulting ion heating through equipartition. Plasma temperature and current profile controls with highly localized heating become advanced techniques to improve plasma confinement and to suppress some MHD instabilities. ECRH is also an ultimate candidate of a steady-state plasma sustainment.

We developed a 4/spl times/4 high-speed optical switch subsystem with variable optical attenuation (VOA). This switch subsystem allows high-speed level adjustment as well as high-speed switching by using the electro-optic (EO) effect of PLZT. We demonstrate 5.5-/spl mu/s switching with VOA to obtain the desired output power for optical burst switching (OBS).

Recently, LaGaO/sub 3/ based perovskite material of La/sub 1-x/Sr/sub x/Ga/sub 1-y-z/Mg/sub y/Co/sub z/O/sub 3-(x+y+z)/ (LSGMCO) has been considered as one of promising candidates for an electrolyte of solid oxide fuel cell (SOFC) due to its high oxygen ion conductivity. LSGMCO electrolyte films were deposited on porous anode of Ni and NiO+Ce/sub 0.8/Sm/sub 0.2/O/sub 1.9/ by pulsed laser deposition method. The LSGMCO film deposited at the substrate temperature of 800 /spl deg/C and the oxygen pressure of 20 Pa (72000 laser pulses) had columnar crystallized structures with large boundaries. The LSGMCO film had the high oxygen ion conductivity of 0.7 S/cm at a measurement temperature of 800 /spl deg/C. Open circuit voltage could be measured from our tube type SOFC unit cell utilizing the LSGMCO electrolyte film, however the value was smaller than theoretical one. We found that control of grain size by adjusting the oxygen pressure was needed for the lower temperature operating anode - support SOFC.

This paper tries to realize the backward double salto. This is more difficult and challenging than the backward single salto by a self-standing horizontal bar exercise robot discussed in a previous paper. The present robot has three links that are connected with two rotational joints and driven by two DC motors controlled by a PD-control law. The backward double salto needs 7.3 rad/s over the horizontal bar in the simulation. First, a control method is shown that accelerates rotation around the horizontal bar within two forward giant swings. Finally, experimental results demonstrate a backward double salto which is consistent with the simulated one.

We have studied two kinds of dual-mode laser diode devices with external optical input signals and found out an all-optical "digital" inverter action in each device. The MLLD-based photonic inverter exhibited extremely abrupt /spl mu/W-class switching characteristics which are expected to lead to the 2R actions in a simple and cost-effective way. We have confirmed its dynamic operation for a 155.52 Mb/s NRZ PRBS data stream and its 3 dB bandwidth of 1.8 GHz. A DFB-LD-based photonic inverter has been examined also and a little higher operation speed (2.8 GHz) has been derived in accordance with its higher relaxation oscillation frequency. We believe that this scheme has potential for practical and cost-effective applications in the future photonic networks although one needs to improve its noise suppression functionality and operation speed.

To study polarized radiative transfer of electron cyclotron waves, a general equation of polarization evolution that includes the effects of both birefringence and dichroism is dealt with. Full Stokes parameters are used to describe the polarization state and the absorption rate in the equation. The evolution equation on polarization state is able to treat general cases in which two polarization states of eigenmodes are not necessary to be orthogonal. Using this equation, a single absorption rate in second harmonic electron cyclotron heating is investigated on the Large Helical Device.

Formation of electron transport barrier and achievement of central electron temperature of more than 10 keV are confirmed by electron cyclotron heating (ECH) in LHD. These are the result of highly concentration of the deposited power. The system are described which enables these experiments and clarifying the mechanisms of the formation of electron transport barrier. The formation of the transport barrier in LHD is limited in rather low density of below 5 × 1018 m−3 so far. The efforts and their results of further optimization of ECH system for the better understanding and for the formation in wider plasma parameters of the transport barrier are also discussed.