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The conceptual design of a heavy ion beam probe (HIBP) for HL-2M tokamak has been proposed to measure the plasma potential, electron density and their fluctuations to contribute to the understanding of advanced confinement modes and transport. Beam trajectory calculations are performed under 3D magnetic field and engineering conditions of the facility. By choosing the positions and angles of both primary and secondary beamlines, a wide region of observation area ( 0.1 r / a 0.9 ) is achieved with 2 MeV Tl + beam injection. The active trajectory control technique is used to obtain the poloidal sweep angle between − 10 ∘ and 10 ∘ . Then, the applied voltages of sweep plates are evaluated to be up to 25 kV. By integrating ionization and attenuation along beam paths, the detected signal level distribution in the plasma density condition n 0 = 5 × 10 19 m − 3 is higher than 100 nA with 100 μ A injection beam intensity in most of the plasma region, which ensures an acceptable signal-to-noise ratio for measurements.

In JFT-2M, the applicability of reduced activation ferritic steel to a fusion demonstration reactor has been demonstrated mainly concerning the ferromagnetic effect on plasma production, control, stability and confinement. The compatibility of the close ferritic wall with high-normalized beta plasmas has been investigated mainly because the demonstration reactor will utilize the wall stabilization effect. Due to improvements in the operation scenario and the modification of the guard limiter configuration, the region showing good compatibility was extended to the closer wall position (the wall position was normalized to the plasma minor radius; rwall/a~ 1.25) and the higher normalized beta (βN ~ 3.5), compared with the previous works with the relatively far wall position and stronger magnetic field (Tsuzuki K. et al 2003 Nucl. Fusion. 43 1288). A reduction in the growth rate of the instability was also observed in the close wall case, which presumably corresponds to the wall stabilization effect, similar to a resistive wall without ferromagnetism.

Compatibility between plasma and reduced activation ferritic steel, which is the leading candidate for the structural material of a fusion demonstration reactor, has been investigated in the Advanced Material Tokamak EXperiment (AMTEX). Ferritic plates (FPs) were installed progressively in the JFT-2M tokamak. The effect of ferromagnetism on plasma production, control, confinement, and stability has been investigated. Impurity release behavior has also been investigated. Even when the inside vacuum vessel wall was fully covered with the FPs and the tokamak plasma was operated close to the wall, no deleterious effect was observed, and the normalized beta could be increased up to ~3.5. Thus, encouraging results are obtained for application of this material to the demonstration reactor.

A key feature of the 'high recycling steady' (HRS) H-mode regimes is the reduction of the transient heat load to the divertor target due to large ELMs. The heat flux to the divertor targets measured by means of a Langmuir probe in the scrape-off layer on the target plate is about ~0.3 MW m−2 in the typical HRS plasmas, which is very small in comparison with the transient heat load in the ELMy H-mode discharge. In addition, the effects of the plasma shaping on the access to and improved plasma performance of HRS H-mode regimes have been investigated. Furthermore, simultaneous measurements of both density fluctuations and potential profiles at the plasma edge region using a heavy ion beam probe are also presented.

The Large Helical Device is a heliotron device with L = 2 and M = 10 continuous helical coils with a major radius of 3.5–4.1 m, a minor radius of 0.6 m and a toroidal field of 0.5–3 T, which is a candidate among toroidal magnetic confinement systems for a steady state thermonuclear fusion reactor. There has been significant progress in extending the plasma operational regime in various plasma parameters by neutral beam injection with a power of 13 MW and electron cyclotron heating (ECH) with a power of 2 MW. The electron and ion temperatures have reached up to 10 keV in the collisionless regime, and the maximum electron density, the volume averaged beta value and stored energy are 2.4 × 1020 m−3, 4.1% and 1.3 MJ, respectively. In the last two years, intensive studies of the magnetohydrodynamics stability providing access to the high beta regime and of healing of the magnetic island in comparison with the neoclassical tearing mode in tokamaks have been conducted. Local island divertor experiments have also been performed to control the edge plasma aimed at confinement improvement. As for transport study, transient transport analysis was executed for a plasma with an internal transport barrier and a magnetic island. The high ion temperature plasma was obtained by adding impurities to the plasma to keep the power deposition to the ions reasonably high even at a very low density. By injecting 72 kW of ECH power, the plasma was sustained for 756 s without serious problems of impurities or recycling.

Results of coherent edge fluctuation measurements using three diagnostics (a reciprocating Langmuir probe, a two channel O-mode reflectometer, and fast magnetic probes) in H-mode discharges on JFT-2M are presented. In discharges in which a high recycling steady (HRS) H-mode phase is obtained through a transient phase with slightly enhanced Dα intensity, two types of coherent fluctuations are observed. The higher frequency mode (around 300 kHz) is the high frequency mode (HFM) observed in the HRS H-mode (Kamiya K et al 2003 9th IAEA Tech. Meeting H-mode Workshop Topic B-14). The lower frequency mode has a frequency of around 80 kHz. The HFM is detected by a Langmuir probe over a wide region in the SOL, as well as by the reflectometer and magnetic probes. However, the HFM is not detected by the higher frequency (38 GHz) channel of the reflectometer after the HRS transition, suggesting that the HFM is not located deeply inside the plasma. The 80 kHz mode is detected by both channels of the reflectometer and by a Langmuir probe, but not by magnetic probes, suggesting that it is an electrostatic mode. In contrast to the HFM, the 80 kHz mode is detected by the Langmuir probe only near the separatrix during the transient phase, which leads to either the HRS phase or the ELMy phase, and is similar to the fluctuations reported in Shinohara K et al (1998 J. Plasma Fusion Res. 74 607).

The large helical device (LHD) is the world largest helical system having all superconducting coils. After completion of LHD in 1998, six experimental campaigns have been carried out successfully. The maximum stored energy, central electron temperature, and volume averaged beta value are 1.16 MJ, 10 keV, and 3.2%, respectively. The confinement time of the LHD plasma appears to be equivalent to that of tokamaks. One of the most important missions for LHD is to prove steady-state operation, which is also significant to international thermonuclear experimental reactor (ITER) and to future fusion reactors. LHD is quite appropriate for this purpose based upon the beneficial feature of a helical system, that is, no necessity of the plasma current. So far, the plasma discharge duration was achieved up to 150 s. The plasma density was kept constant by feedback control of gas puffing with real time information of the line density. The issue for demonstrating steady-state operation is whether divertor function to control particle and heat flux is effective enough. Relevant to this, LHD diagnostics should be consistent with the following: 1) continuous operation of main diagnostics during long-pulse operation for feedback control and physics understanding; 2) measurement of fraction of H, He, and impurities in the plasma; 3) heat removal and measure against possible damage or surface erosion of diagnostic components inside of the vacuum chamber; 4) data acquisition system for handling real time data display and a huge amount of data. Although there are already some achievements on the above subjects, there remain still several issues to be resolved. On the other hand, the long-pulse operation of the plasma gives benefits to the diagnostics. For example, the polarizing angle of ECE emission can be changed during the discharge, and the intensity dependence on the polarizing angle has been obtained. The spatial scanning of the neutral particle analyzer and the spectrometer can supply the spatial profiles of the fast neutral particle flux and the specific impurity lines. In this paper, the present status of these issues and future plans are described.

Compatibility between the plasma and low activation ferritic steel, which is a candidate material for fusion demonstration reactors, has been investigated step by step in the JFT-2M tokamak. We have entered the third stage of the Advanced Material Tokamak EXperiment (AMTEX), where the inside of the vacuum vessel wall is completely covered with ferritic steel plates ferritic inside wall (FIW). The effects of a FIW on the plasma production, impurity release, the operation region, and H-mode characteristics have been investigated. No negative effect has been observed up to now. A high normalized beta plasma of βN ~ 3, having both an internal transport barrier and a steady H-mode edge was obtained. A remarkable reduction in ripple trapped loss from 0.26 MW m−2 (without ferritic steel) to less than 0.01 MW m−2 was demonstrated by the optimization of the thickness profile of FIW. A code to calculate fast ion losses, taking into account the full three-dimensional magnetic structure was developed, and values obtained using the code showed good agreement with experimental results. Thus, encouraging results are obtained for the use of this material in the demo-reactor.

Reactions of carbonaceous materials (activated carbon, graphite, and lignin) with carbon dioxide were carried out at 973 K using alkali metal carbonates (m.p. 891∼1164 K) and eutectic mixtures of these compounds (m.p. 669∼787 K) as catalysts. The reaction occurred when the carbonate catalysts were physically mixed with carbonaceous materials and the melting points of the catalysts were lower than the reaction temperature. However, the reaction did not proceed with physically mixed catalysts when the melting points of the catalysts were higher than the reaction temperature. Repeated use of the molten catalyst was also studied to investigate the possibility of continuous gasification of carbonaceous materials. After the activated carbon (or lignin) was consumed in a batch reactor, the same amount was added in the reactor containing the catalyst and the reaction started again. It was found that the eutectic molten catalyst could be reused without any loss of its catalytic activity by repeating this operation.

This paper reports on the behaviour of high-energy ions created by ion cyclotron range of frequency (ICRF) heating on the Large Helical Device (LHD). In the third experimental campaign conducted in 1999, it was found that minority heating has good heating performance, and high-energy particles were observed. In the fourth campaign in 2000, the temporal behaviour of high-energy ions was investigated in the minority heating regime using turnoff or modulation of ICRF power. The time evolution of the high-energy particle distribution was measured using a natural diamond detector (NDD) and a time-of-flight neutral particle analyser (TOF-NPA). It was found that the count number of higher-energy particles declines faster than that of lower-energy particles after ICRF turnoff. In the modulation experiments, the phase difference of the flux of high-energy particles with respect to the ICRF power modulation increased with energy. These results were explained qualitatively by the Fokker-Planck equation with a simple model. The pitch-angle dependence of the distribution function was also measured in the experiment by changing the line of sight of the TOF-NPA, and an anisotropy of the high-energy tail was found. This anisotropy was reproduced by solving the bounce-averaged Fokker-Planck equation. The second harmonic heating was conducted successfully for the first time in the LHD in high-β plasma, and high-energy particles were also detected in this heating regime.

Ion cyclotron heating has been established as one of the heating schemes in nuclear fusion research and its use in steady state plasma heating in various devices is being considered. The optimal technology for steady state ion cyclotron range of frequency heating has not been firmly established. This article reports on the liquid stub tuner which was newly developed in research and development activities on the large helical device. It demonstrated high performance in real use in experiments. Two different impedance-matching systems based on the liquid stub tuner are studied: one is a triple liquid stub tuner system and the other is a single stub tuner system with a liquid phase shifter. The characteristics of the two systems are compared from the points of view of how wide a frequency range is covered, and how great the reduction of the voltage in the transmission line is.

Potential and density/temperature fluctuations at the L-H transition are measured by a heavy ion beam probe (HIBP) on JFT-2M. It has been observed that the time scale of potential change is as fast as 10-100 µs when the input power (Pin) is larger than the L-H threshold power (Pth). When Pin = Pth, the confinement is improved step by step, with sawteeth crashes accompanied by a decrease of potential. After a few sawteeth crashes, the potential drops rapidly to the level of the ELM-free H-mode. At that time, the density/temperature fluctuations are suppressed simultaneously. The observations of the temporal behaviour of the potential and fluctuations in such an L-H transition are reported.

Ion cyclotron range of frequency (ICRF) heating on the large helical device (LHD) is characterized by high power (up to 12 MW) and steady state operation (30 min). The LHD is a helical device (with a major radius of 3.9 m and a minor radius of 0.6 m) with superconducting coil windings (l=2, m=10). The main purpose of physical research is to investigate currentless and disruption-free plasma. Research and development for steady state ICRF heating has been carried out in recent years: A high rf power transmission system consisting of stub tuners, a ceramic feedthrough, and an ion cyclotron heating loop antenna has been developed. In addition, steady state operation of a rf oscillator has been achieved at a power higher than 1 MW. A liquid stub tuner has been proposed as an innovation. The liquid stub tuner makes use of the difference between the rf wavelengths in liquid and in gas due to the different relative dielectric constants. The liquid stub tuner has been experimentally proved to be a reliable rf com...

Steady-state ion cyclotron range of frequency (ICRF) heating technologies have been developed to heat plasma for >30 min in the Large Helical Device (LHD). Steady-state-operation tests of high volt...

Ion Cyclotron Range of Frequency (ICRF) heating on Large Helical Device (LHD) is characterized by its high power (up to 12MW) and by steady state operation (30 minutes). The LHD is a helical device (with a major radius of 3.9 m and a minor radius of 0.6m) with super-conducting coil windings (l=2, m=10). The main physical purpose is to investigate currentless and disruption-free steady state plasmas. Research and development for ICRF heating have been carried out in recent years. A high RF power transmission system has been developed, which consists of stub tuners, ceramic feed-through and ICRF heating loop antenna. The RF transmission system was tested and withstood 58kV for 10 seconds and 40kV for 30 minutes. The RF voltage corresponds in the case of a plasma loading resistance, 5Ω to a transmitted RF power capability of 3.4MW and 1.6MW. In addition, a pre-matching stub tuner was very effective in reducing the RF voltage. The reduction rate was confirmed to be one third, which leads to a higher ICRF injection efficiency because of reduction of RF power loss in the transmission system. Furthermore a proper procedure to effectively carry out aging of the RF antenna was found in terms of selecting the RF pulse length, repetition rate and RF voltage.

The performance of a strained InGaAs/InAlAs multiple-quantum-well (MQW) electroabsorption (EA) modulator was evaluated theoretically and experimentally, The theoretical analysis showed that adding tensile strain to the InGaAs wells widens the wells and reduces the driving voltage; it also showed that adding compressive strain to the InAlAs barriers reduces the band discontinuities and increases the optical saturation power. A fabricated InGaAs/InAlAs MQW modulator with tensile strain in the wells and compressive strain in the barriers had a large modulation bandwidth (f/sub 3 dB/>20 GHz) and a lower driving voltage (V/sub 15 dB/=1.2 V) compared to an unstrained InGaAs/InAlAs MQW modulator, so it had a higher modulation efficiency (17 GHz/V). This strained MQW modulator produced a 10 Gb/s optical signal with a clear eye opening and small chirping (/spl alpha//sub eff/=0.6). Moreover, it had shorter carrier escape times, so it has better optical saturation behavior. Introducing strain thus significantly improves the performance of the MQW-EA modulators.

Integrating the input and output waveguides with a multiple-quantum-well (MQW) electro-absorption (EA) optical modulator is shown to achieve ultra-high-speed modulation while keeping the total device length long enough for easy fabrication and packaging. Testing with fabricated modulators showed that a shorter modulation region results in a larger modulation bandwidth. The additional loss due to the waveguide integration was less than 1 dB. An optimized modulator showed a large modulation bandwidth of 50 GHz, a low driving voltage of less than 3 V, and a low insertion loss of 8 dB. A prototype module of this modulator had a bandwidth of greater than 40 GHz. Optimizing the MQW structure makes the modulator insensitive to polarization. These results demonstrate that MQW-EA modulators with integrated waveguides are advantageous in terms of fabrication, packaging, and ultra-high-speed modulation.

Beam-driven Alfvén eigenmodes (AEs) have been studied in the TJ-II low-magnetic-shear flexible heliac (B 0 = 0.95 T, 〈R〉 = 1.5 m, 〈a〉 = 0.22 m), in L-mode hydrogen plasmas with hydrogen NBI and ECR heating (P NBI ⩽ 1.0 MW, E NBI = 32 keV, P ECRH ⩽ 0.6 MW). In low-density plasmas in the range n e ¯ = (0.3–1.5) × 1019 m−3, a large variety of AEs have been observed in the plasma core with the heavy ion beam probe diagnostic and Mirnov coils, in the frequency range 50 kHz f AE ι is varied during the shot (dynamic configuration scan), some AEs exhibit changes in their nonlinear evolution from bursting-amplitude AEs with chirping frequency to steady-frequency AEs, and back. The range of ι intervals within which the AEs studied are chirping or steady-state is determined.

Vertical-cavity surface-emitting lasers (VCSELs) emitting at 1.3-μm are potentially attractive for optical interconnects. The advantages of such lasers include their lower driving current, a surface-mountable device structure, and a narrow circular output beam that is ideal for a polymer multimode waveguide on a printed circuit board [1]. Accordingly, there has been a widespread interest in developing 1.3-μm VCSELs [2,3] and a novel type of VCSEL, which is a lens-integrated surface-emitting laser that consists of a short InGaAlAs multiple-quantum-well (MQW) distributed feedback laser (DFB) active stripe integrated with a 45° mirror and an aspheric lens [4,5]. Here, we propose a novel 1.3-μm quantum dot (QD) surface emitting laser (SEL), which consists of a QD laser section and a polymer optical circuit (POC) section. A QD laser emitting at 1.3 μm needs to have a lower operation power and temperature insensitive operation because of the discrete energy state. A suitable POC design can be used to control the emitting place, direction, and beam profile of a laser. Moreover, POCs are easy to fabricate and are less expensive owing to the low cost of polymer material. In this work, we propose a QD SEL using a POC, which consists of a polymer optical waveguide, spot-size converter, and 45° metal mirror. We designed the polymer spot-size converter to match the laser beam profile using the optical polymer waveguide. We were able to realize the operation of a QD SEL using a POC.

Low-frequency electronic Raman scattering in La 2-x Sr x CuO 4 has been investigated over a wide compositional region, 0≤x≤0.34, covering the insulating, superconducting, and non-superconducting metallic compounds. We have found that the scattering intensity for the (xy) polarization predominates over that of the (x'y') polarization in the low-doping region below x≤0.15, but vice versa at higher doping levels. The results indicate that anisotropy in the effective-mass tensor (or k-space dispersion) of the carriers changes systematically with hole doping, in contradiction with the simple band picture

The charge-transfer (CT)-type optical excitations from O 2{ital p} to Cu 3{ital d} and to Cu 4{ital s} states have been observed around 1.5 and 5.0 eV, respectively, in undoped {ital T}{prime}-phase {ital L}{sub 2} CuO{sub 4} single crystals, where {ital L}=Pr, Nd, Sm, Eu, or Gd. The spectral shapes of these CT excitations are greatly modified upon electron doping by Ce substitution for the {ital L} sites. The CT excitation energies in a series of {ital L}{sub 2}CuO{sub 4} compounds with the {ital T}, {ital T}{sup *}, and {ital T}{prime} structure strongly depend on the {ital L} species, indicating the crucial effect of the in-plane Cu-O bond-length variation as well as of the Cu-O coordination on the electronic states in the CuO{sub 2} sheets.

Optical-phonon spectra were investigated for single crystals of the parent materials of various cuprate superconductors and related materials. Comparing the spectra, all the observed phonons were unambiguously assigned. It was found that the main phonon modes in the CuO{sub 2} plane, the Cu-O stretching and bending modes, exhibit completely different dependences of their frequency on the Cu-O bond distance {ital a}/2; that is, the former shows strong {ital a} dependence while the latter is relatively insensitive to {ital a}. From a quantitative analysis of the spectra, the highly covalent character of these layered cuprates was confirmed. The remarkable change of the stretching-mode frequency against {ital a} indicates a direct coupling of this phonon with the Cu-O charge-transfer electronic excitation.

The optical phonon spectra were investigated for single crystals of various insulating copper oxides with a single CuO 2 plane, mainly for the (214)-compounds with the T-, T′- and T ∗ - structures which became superconducting by hole/electron doping. Comparing their spectra with other cuprates, (Ca, Sr)CuO 2 and Sr 2 CuO 2 Cl 2 , all the phonon modes in the ab -direction have been assigned unambiguously. From the phonon parameters, which were obtained by the oscillator fit to the experimental data, the oxygen effective charge was estimated for each material. The relatively small values of the effective charge indicate a highly covalent character in this class of materials, which should be essential for high- T c superconductivity.

Spectra of optical conductivity and magnon Raman scattering have been investigated in single crystals of a parent family of cuprate superconductors with various types of Cu-O single-layer networks. The analysis of the spectra shows the systematic dependence of the charge-transfer gaps and covalent character of Cu-O bonds on the pattern of the Cu-O network, while the spin-exchange energy is rather convergent for all the single-${\mathrm{CuO}}_{2}$-sheet compounds.

A resistive interchange mode of the m=1/n=1 ?> structure ( m ?> , n ?> : poloidal and toroidal mode numbers, respectively) with a bursting character and rapid frequency chirping in the range less than 10 kHz is observed for the first time in the edge region of the net current-free, low beta LHD (Large Helical Device) plasmas during high power injection of perpendicular neutral beams. The mode resonates with the precession motion of helically trapped energetic ions (EPs), following the resonant condition. The radial mode structure is recognized to be similar to that of the pressure-driven resistive interchange mode, of which radial displacement eigenfunction quite localizes around the mode rational surface, and evolves into an odd-type (or island-type) during the late of frequency chirping phase. This beam driven mode is excited when the beta value of helically trapped EPs exceeds a certain threshold. This instability is thought to be a new branch of resistive interchange mode destabilized by the trapped energetic ions. The radial transport, i.e. redistribution and losses, of helically trapped energetic ions induced by the mode transiently generates significant radial electric field near the plasma peripheral region. The large shear of thus generated radial electric field is thought to contribute to the observed suppression of micro-turbulence and transient increases of the temperature of fully ionized carbon impurity ions and electron density, suggesting improvement of bulk plasma confinement.

The discharge scenario of high temperature plasma with a helical configuration has significantly progressed. The increase of central ion temperature due to the reduction of wall recycling was clearly observed. The peaking of the ion heating profile and the reduction of charge exchange loss of energetic ions play an important role for further improvement of ion heat transport in the ion internal transport barrier (ITB) core. The ion ITB and electron ITB have been successfully integrated due to the superposition of centrally focused electron cyclotron heating to the ion ITB plasma, and the high temperature regime of the ion temperature comparable to the electron temperature (Ti ~ Te) has been significantly extended. The width of the ion ITB formed with electron ITB is wider than the width of electron ITB. The positive radial electric field was observed in the integrated ITB plasma by a heavy ion beam probe, while the negative radial electric field was observed in ion ITB plasmas. The ion temperature gradient decreases with the increase of the temperature ratio (Te /Ti).

As a key component of a strontium based optical clock, we have developed an apparatus which allows laser cooling and trapping of more than 10/sup 7/ /sup 88/Sr atoms to temperatures below 1 /spl mu/K. Using this system, we have performed the first high accuracy measurement of the /sup 88/Sr /sup 1/S/sub 0/-/sup 3/P/sub 1/ clock transition using an ultra-cold sample. Detailed descriptions of both the measurement technique and corresponding systematic uncertainties is provided. In addition, by varying the density of the ultra-cold /sup 88/Sr sample over a range of three orders of magnitude we obtain the first definitive measurement of a density-related frequency shift and linewidth broadening of an optical clock transition in an ultra-cold alkaline earth system. Spectroscopy of the /sub 1/S/sub 0/-/sup 3/P/sub 0/ transition is currently underway using this narrow probe laser and an octave spanning femtosecond laser. Our most recent results are presented. The proposed measurement technique, accuracy, and stability of an optical clock based on the EIT (electromagnetically-induced-transparency) measurement in /sup 88/Sr are described.

EA-modulator integrated DFB lasers have become one of the key devices in multigigabit long-distance lightwave communications. [1, 2] Recently, a new method of integrating photonic devices has been proposed, using the in-plane local bandgap energy control of the MQW structures during simultaneous selective area growth (SAG) by MOCVD. [3, 4] This technique offers a high optical coupling efficiency as well as reproducible fabrication, which are essential in such optical integrated devices. This paper describes an MQW EA-modulator integrated with a DFB laser, fabricated by SAG and a semi-insulating BH process, aimed at a high on/off ratio and high-speed operation.

Polymeric 1/spl times/8 digital optical switch using highly reliable fluoride polyimide has been demonstrated. Experimental results show an excellent potential for the practical use in optical networks.

The ICRF heating is planned at 3MW with 30min and 12MW with 10sec on the Large Helical Device, which is now being constructed and whose first plasma is scheduled in 1998. For that purpose, we are researching and developing several issues such as high power/long pulse RF oscillator, ceramic feed-through, liquid stub tuner and feedback control for impedance matching etc. Recent results acquired so far are as follow; (1)1.6MW/5000sec and 1.9MW/10sec operation of RF oscillator, (2)45kV/1200sec and 54kV/10sec operations in liquid stub tuner, (3)34kV/1740sec and 38kV/615sec operation in ICRF heating system and (4)verification of feedback control for impedance matching by frequency modulation and liquid stub tuner.

Alfven eigenmode (AE) activity driven by NBI-produced fast ions is observed in TJ-II plasmas. A two-step response of the measured AEs to electron cyclotron heating (ECH) power is seen. In a first step, the continuous character of the unstable AEs changes to a chirping character of the marginally unstable AEs when moderate values of ECH power are applied to the NBI-only-heated plasma. In a second step, a significant reduction of the AE amplitude is observed when the ECH power is doubled. This stabilizing effect has been experimentally confirmed both on a shot-by-shot basis and along a single discharge by means of ECH modulation. The observed stabilizing effect is stronger with on-axis ECH than with off-axis ECH power injection.

A central ion temperature of 7 keV in a neutral beam injection (NBI)-heated plasma and a central-electron temperature of 20 keV in an electron cyclotron resonance heating plasma were achieved in the Large Helical Device (LHD) using an upgraded heating system with a newly installed perpendicular-NB injector and gyrotrons. The values of Ti and Te significantly exceeded 5.6 and 15 keV, obtained in previous experiments, respectively. High-Ti plasma was obtained using a carbon pellet injection and the kinetic-energy confinement improved by a factor of 1.5. Transport analysis of the high-Ti plasmas showed that the ion-thermal diffusivity and the viscosity were reduced after the pellet injection. Dynamic-transport analysis is applied and the transition to the ion-internal-transport barrier and back transition are discussed.

Electrode biasing experiments were carried out in various magnetic configurations on the Large Helical Device (LHD). The transitions of poloidal viscosity, which were accompanied with bifurcation phenomena characterized by a negative resistance in an electrode characteristic, were clearly observed on LHD by the electrode biasing. The critical external driving force required for transition was compared with the local maximum in ion viscosity, and the radial resistivity before the transition also compared with the expected value from a neoclassical theory. The critical driving force increased and the radial resistivity decreased with the major radius of the magnetic axis Rax going outwards. The configuration dependence of the transition condition and the radial resistivity qualitatively agreed with neoclassical theories. The radial electric field and the viscosity were also evaluated by the neoclassical transport code for a non-axisymmetric system, and estimated electrode voltage required for the transition, which was consistent with the experimental results.

As the clinical use of positron emission tomography technology grows, so does the demand for noninvasive measurement of cerebral blood flow (CBF). This chapter presents the development of a compact radiation monitor composed of dual β-detectors suitable for the detection of radiation from superficial tissue. One detector is placed over the wrist above the radial artery to monitor arterial radioactivity, whereas another was placed on an adjacent skin area to measure the background. The monitor worked fairly well except on obese subjects, for whom an arterial count curve was not recoverable. A model has been developed to restore the arterial input function comparing the two-detector response with time that incorporated the superficial tissue flow, mainly of skin and the subcutaneous tissue. Twenty-four studies on five normal volunteers are conducted with [ 15 O]-water slow bolus injections, which are controlled by an automatic injection system. A significant correlation is obtained between the calculated CBF using restored input function by the system and the CBF using an actual arterial input curve by arterial cannulation. Further, refinement of the procedures that include the calibration of restored arterial input to well counter and accurate correction of dispersion in the restored arterial input may increase the accuracy of this noninvasive method.

The transition to the improved confinement mode by electrode biasing was observed for the first time in the Large Helical Device (LHD). A negative resistance was observed in the confinement mode sustained by the cold electrode biasing. The electrode current showed a clear decrease against an increase in the electrode voltage and was characterized by a hysteresis in the transition phenomena. The decrease in the electrode current suggested an improvement in the radial particle transport. An increase in the energy confinement time and remarkable suppression of density fluctuations, which correspond to the transition, were also observed. These results indicated that the electrode biased plasma in LHD showed similar improvements in confinement to those in the H-mode plasmas in tokamaks and stellarators.

A heavy ion beam probe (HIBP) system has been installed into the Large Helical Device (LHD) to measure the spatial profile of the plasma potential and density fluctuations. The optimization of the HIBP system, especially the beam injector, is described. The negative ion beam is required for the MeV beam production in a tandem accelerator. A sputter-type heavy negative ion source has been developed as an intense Au(-) beam source to produce Au(+) beams with energy in the MeV range. The extraction electrodes and the Einzel lens system of the ion source have been designed taking into account the beam optics, and installed into the real machine. Throughout the plasma diagnostics on LHD experiments, the consumptions of vaporized caesium and gold target are being characterized for practical operations. In addition, the experimental charge fractions are compared with the theoretical fractions for understanding the charge-changing behavior of Au(-) ions and optimizing the fraction of Au(+) ions at the exit of the tandem accelerator of the HIBP system.

The optical reflectivity spectra for single crystals of La2-xSrxCuO4 were investigated at room temperature over a wide energy range from far-infrared to vacuum ultraviolet and over a wide x-range 0≤x≤0.34. With increasing Sr-content, the spectral weight moves from the charge-transfer excitation to the lower energy part which seems to consist of two components, a Drude-like component and a mid-infrared peak. In the heavily doped region both components seems to be combined into a single Drude-like absorption. Based on these observation the electronic state characteristics of the high-Tc cuprates are discussed.

Single crystals of parent families of oxide superconductors with single CuO2-sheets have been synthesized and their optical spectra for charge-transfer and two-magnon excitations have been measured to unravel the puzzling electronic structure. The effect of electron-doping on the charge- transfer gap has been also investigated for Nd2-xCexCuO4 compounds.

Electron loss cross sections of Au+ and Au2+ by electron and proton impact are calculated by using respectively the Lotz formula and the LOSS and CAPTURE computer codes. The corresponding rate coefficients have also been calculated. Using this information, the signal levels of heavy ion beam probe in the Large Helical Device are estimated. The calculated beam currents at the detector position are compared with the detected beam currents in the MeV energy range for a plasma electron density of 1 × 1019 m-3 and electron temperature of 1.5 keV. The obtained cross section / rate coefficient data can also be used for reconstruction of electron density and temperature profiles.

The authors propose and demonstrate the use of compressively strained barriers to reduce photogenerated carrier sweep-out times in In x Ga l-x As/In y Al l-y As multiquantum well modulators, designed for λ=1.55 μm

The physical properties of Ba 1− x K x BiO 3 including transport coefficients, optical spectra, Raman spectra, the upper critical field and superconducting energy gap were measured on thin films. From the experimental results, we firmly conclude that the Ba 1−x K x BiO 3 is close to a band metal in its metallic phase and the superconductivity is of BCS-type.

3d transition-metal oxides with perovskite and K 2 NiF 4 crystal structures, (La,Sr)VO 3 , (La,Sr)FeO 3 , (La,Sr)CoO 3 , LaNiO 3 and (La,Sr) 2 NiO 4 systems are investigated focusing on the effect of carrier doping performed by the A-site ion substitution. Both (La,Sr)VO 3 and (La,Sr)CoO 3 systems show an insulator to metal transition by Sr substitution, however, the magnetic behavior differs drastically. The mid-infrared structure induced by Sr substitution is observed in the optical spectra of (La,Sr) 2 NiO 4 system. Relation between the behavior of metal-insulator transition and the variation of the electronic and/or spin structure in these systems is discussed in comparison with the high-T c copper oxides.

We have investigated spectra of optical conductivity for single crystals of Pr 2− x Ce x CuO 4−δ with varying x and δ. In comparison with LaSrCuO system, the growth of a ‘Drude’ part is observed to be much slower. It seems consistent with the difference of the electronic phase diagram between the two systems. LaSrCuO and PrCeCuO, where the metal-insulator transition occurs at x c ≈ 0.06 and at x c ≈ 0.14, respectively. Neverthless, the spectral weight of charge transfer (CT) excitation of Pr 2 CuO 4 is readily transferred to ‘mid-IR’ region with a small amount of Ce-substitution ( x x c or oxygen defects. It indicates that the elecstronic state in the CuO 2 sheet is seriously affected by electron-doping even though the compound remains to be an antiferromagnetic insulator. This investigation also indicates that oxygen deficiencies certainly introduces extra electron-carriers.

The spin and doped charge states in copper oxide superconductors were investigated by Raman spectroscopy. The anomalous magnon scattering in the antiferromagnetic insulator phases, such as the second peaks near 4J (J is the two-spin superexchange energy) in the B1g spectra and the large scattering intensities in the A1g spectra, suggests the existence of four-spin cyclic exchange interactions. When carriers are doped, the A1g spectra show non-“normal Fermi liquid” behavior. The imaginary part of the experimentally obtained susceptibility have ω-proportional part from ω~0. The gradient increases, on cooling, as in the case of the marginal Fermi liquid.

Optical reflectivity spectra are investigated on single crystals of La 2- x Sr x CuO 4 over a wide compositional range 0 ≤ x ≤ 0.34 which covers insulating, superconducting and ‘normal’ metallic phases. It is clearly demonstrated that the electronic structure exhibits drastic changes at x ~ 0 and at x ~ 0.25, starting from the x = 0 insulator with a charge-transfer energy gap and approaching a Fermi liquid state for heavy doping.

An MQW electroabsorption-modulator integrated DFB laser fabricated by using the in-plane bandgap energy control technique and a low-capacitance semi-insulating BH process is presented. This device has a threshold current as low as 5.4 mA and a modulation efficiency as high as 13 dB/2V. Modulation at 10 Gbit/s with a modulation voltage of only 1V peak to peak demonstrates the potential value of this device for electroabsorption modulation at 1.55 μm.

ZnSe layers were grown epitaxially on (111)ZnSe substrates in a closed tube from a Ga solution by the temperature difference method. The grown layer under the condition that the substrate temperature was 1000°C showed strong blue emission even at room temperature. On the other hand, the layer at a lower substrate temperature and that obtained by the gradual temperature lowering method looked orange to the eye at room temperature, which are related to the Zn vacancy. In conclusion the room temperature blue emission from ZnSe epitaxial layer was obtained by controlling Zn vapor pressure during the crystal growth.

Transport and magnetic properties of (${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${)}_{2}$${\mathrm{CuO}}_{4}$ are systematically investigated over a wide composition range up to x=0.175 including a nonsuperconducting metal phase in the heavily doped region. Remarkable changes associated with the superconductor-to-nonsuperconductor transition are observed both in the Hall coefficient and the magnetic susceptibility, suggesting the modification of both charge and spin states.