Electron density behavior during the fast termination phase of the post-disruption runaway plasma was investigated for the first time. Increases in electron density after the rst drop of runaway plasma current were observed. At the second current drop, an increase in electron density with density oscillations having a period of ˜1 ms was found. After the second current drop, higher electron density was observed in the case of shorter current decay time.

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The influence of a transient heat load on the formation of hole and bubble structures on tungsten surfaces exposed to helium plasmas is demonstrated using pulsed laser-beam irradiation in divertor simulator NAGDIS-II. SEM (scanning electron microscope) micrographs of the tungsten surface revealed that the formation of the holes and bubbles was dramatically enhanced due to a transient temperature increase in response to the laser irradiation.

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The purpose and recent progress of the Burning Plasma Simulation Initiative (BPSI) are discussed. Simulation of burning plasmas requires integrated modeling of various physics phenomena with wide-ranging spatial and time scales. The activities of the BPSI are of three types: development of the framework for integrated simulation codes, development of integrated modeling of multi-scale physics, and implementation of distributed parallel processing. Similar activities have been reported in the United States and the European Union. Features of the integrated transport code, TASK, being developed as a reference code for BPSI, are also described. Finally, asummary is given and future issues are discussed.

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In an iontrap,laser-cooled ions can be confined in a small space in an ultra-high vacuum so that collisions rarely happen and the ions are well isolated from the environment. Since these conditions enable high-resolution spectroscopy of single ions, laser-cooled ions are suitable for use in developing frequency standards. The ions can be cooled to the motional ground state to give a well-defined initial quantum state for quantum state manipulation and quantum computing. In this review, principles of ion traps and laser cooling, and recent progress in optical frequency standards and quantum computing with trapped ions are described.

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The neutral beams (NB) in JT-60U and LHD are unique systems in the world to clarify the physics necessary to realize ITER and future fusion reactors. There were considerable progresses in these years in the plasma physics research utilizing those existing NB systems, which substantially contributed in the ITER and fusion reactor designs. In the meantime, the operation and tests in the existing systems together with the R&D toward ITER have achieved remarkable breakthroughs and milestones, such as achievement of the ITER relevant high power density beams in the MeV accelerator R&D. The R&D results developed for the existing NB systems have now widely spread in the industries, in particular in Hi-Tech device manufacturing processes, and are supporting technological basis of the IT societies.

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Recent successful results of LHD experiments have relied on the high energy NBI heating that has been achieved by successful development of advanced “negative ion technology”. The LHD experimental results are overviewed and discussed in conjunction with several features of the NBI system. High energy beam (180 keV hydrogen) heats electrons in plasma rather than ions, which is effective for production of high density and high pressure plasma. Tangentially injected beams are confined well in helical magnetic field, which enables plasma initiation by NBI and sustains high beta plasmas. The beam-induced toroidal current is utilized for changing the external magnetic configuration to study the MHD characteristics of the LHD plasma. The recent successful R&D results of the negative-ion-based NBI are also described. By introducing a new grid system and improving the arc efficiency of the ion source, the targeted output power of 5 MW per beamline has been achieved.

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In steady-state tokamak fusion reactors, an efficient external current drive and a large fraction of the bootstrap current are required for non-inductive operation at low circulating power. NBI is a powerful and reliable actuator for the current drive and heating. A negative-ion based NBI (N-NBI) with a high beam energy more than 350 keV has been installed in the JT-60U tokamak in order to study the NBI current drive and heating in an ITER relevant regime. This paper presents recent achievements in N-NBI experiments and progress of the JT-60U N-NBI system for steady-state operation in ITER and tokamak fusion reactors.

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The present ITER NB system includes two design features: short beamline design and vacuum insulated beam source (ion source and accelerator) which sustain 1 MV high voltage under radiation environment. The short beamline design is achieved by subdividing interior of the neutraliser into narrow channels to reduce gas conductance, and hence, the gas flow rate to ensure target thickness required for neutralisation. Optimizing the beam transmission and reionisation loss of neutral beams, the axial length of the ITER NB injector was shortened to be 23.4 m with a reasonably high injection ef ciency. Three-dimensional neutron transport analyses clari ed possible excess power dissipation due to radiation-induced conductivity, if the high voltage is insulated by conventional gas such as SF⁶. Thus, design of vacuum insulated beam source has been established for the present ITER NB system.

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This article reviews R&D progress of a MeV accelerator and a large negative ion source at the Japan Atomic Energy Research Institute (JAERI). The JAERI MeV accelerator at present aims at acceleration of high current density (200 A/m²) H^- ion beams up to MeV range energy. According to the progress of vacuum insulation technology, the MeV accelerator sustained 1 MV for more than two hours stably, followed by beam acceleration experiments of high current density. So far, H^- ions beams of 146 A/m², 836 keV have been obtained, which is the world's first demonstration of “ITER class” high power density beams. Recent investigation of negative ion uniformity in a large negative ion source revealed fast electron leakage through a magnetic filter, followed by destruction of negative ions in the local extraction region during pure volume (without Cs) operation. On the other hand, the leaked fast electrons enhance surface production of negative ions locally under Cs seeded operation. This implies possible high current density and uniform negative ion production by a high-density plasma in the magnetic configuration like positive ion sources, to be coupled with RF driven plasma production for an NB system of a fusion DEMO reactor.

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Technologies of a large ion source developed for neutral beam injectors(NBI) have been applied to various fields of industries such as ion beam machining for semiconductors, electronics and optical devices, and manufacturing process of a large size liquid crystal display. Power supply technology of a high performance core snubber for NBI has also been applied to high energy particle accelerators to improve the efficiency.

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The light sources have been one of the interesting and exciting subjects as plasma applications. Recently the light sources researchers' interest is development of mercury-free discharge light sources from low-pressure to ultra high-pressure discharge. In this paper light sources and research on them are introduced to plasma researchers. The authors expect plasma researchers are interested in plasmas for light sources and research on them.

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Argon-Mercury fluorescent lamp is one of the most old and popular plasma applications. The argon-mercury fluorescent lamp is one of the oldest discharge light sources. Its materials and structure have been modified and improved. Recently new-type of fluorescent lamps, cold cathode fluorescent lamps (CCFL) have become popular as back light of liquid crystal panel display (LCD backlight). In this section basics of fluorescent lamps are described.

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High Intensity Discharge lamps are call as HID Lamps. They have some useful characteristics such as compact light emitting volume, large luminous flux, high efficacy, long life, etc. Instead of these benefits, HID lamps is operated at high pressure with large current. This higher operational temperature causes some issues such as interval time for re-ignition, mechanical break down of envelope, etc. In this paper HID lamps are explained and also its characteristics and application are reviewed.

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As interests in environmental friendly products, demands from market for mercury-free fluorescent lamps become stronger. Xenon is the most expected material as a substitution for mercury for fluorescent lamps. So many researches have been done by so many researchers and recently by using external electrode with conventional discharge tube with internal electrodes droved by pulsed discharge has achieved 90 lm/W and 12000 cd/m². Another effort is using molecular gas as discharge medium. For example Ar-N₂ mixture and CO are proposed.

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Atomic and molecular processes in volumetric recombination phenomena relevant to divertor detachment are investigated in a divertor simulator MAP (Material and Plasma) -II. In the recombining plasmas, quantitative measurements of parameters, especially using a Langmuir probe, are difficult, so that the development of alternative diagnostics is important. Recombination can be induced in He plasma by puffing of He or H₂. In the He puffing case, the Rydberg spectra show an electron temperature of lower than 0.1 eV, while in the H₂ puffing case, the Rydberg spectra disappear even though the reduction of the ion flux is apparent, showing that another type of recombination occurs. Negative hydrogen ions are observed in the peripheral region of the plasma column.

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