The GIOTA code [1] has been applied to clarify the configuration dependence of ripple transport properties in LHD. The effective helical ripple (ε_eff), as a measure of the level of ripple transport, is calculated with a wide range scan of magnetic axis position, (R_ax) and plasma beta value (β). Our results show that ε_eff takes a minimum value in a wide radial portion around the configuration with R_ax = 3.53-3.55 m at vacuum. It is also revealed that ε_eff decreases as β is increased for configurations with R_ax of less than the above mentioned range.

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Development of large-area high-density plasma sources with a scale length of meters is strongly desired for a variety of plasma processes, especially the flat panel display fabrications. Considering design issues for plasma production with high-frequency power sources to satisfy the requirements for enlargement of source-size exceeding a meter, the power deposition profile and hence the plasma distribution become inherently non-uniform, largely due to standing wave effects, which cannot be avoided with increasing source size when the source employs power-coupling devices (inductive antennas or capacitive electrodes) with a scale-length equivalent to or as long as the 1/4 wavelength of the HF-power transmission. In this article, these constraints associated with large-area sources are reviewed, and an inductively coupled RF plasma source with multiple low-inductance antenna (LIA) units is presented as a promising candidate to avoid the problems with conventional sources.

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This article is intended as a short guide to the field of “Langmuir turbulence.” Various theoretical and experimental studies on Langmuir turbulence have been carried out since the 1960s; consequently, a number of its fascinating properties have been uncovered. However, there still remain important unsolved issues in this basic field of plasma physics. In the present article, the history and recent research activities concerning Langmuir turbulence are briefly reviewed.

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A method of design and construction of a measurement system is discussed. Characteristics of a signal, i.e., frequency, amplitude and so on, must be analyzed. An analog signal is digitized by an analog to digital converter. Sampling frequency must be higher than two times of the signal frequency. Control of the digitizer by a computer through several kinds of interfaces is also discussed.

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In fusion experiments, diagnostic control and logging devices are usually connected through the field bus, e.g. GP-IB. Internet technologies are often applied for their remote operation. All equipment and digitizers are driven by pre-programmed sequences, in which clocks and triggers give the essential timing for data acquisition. Data production rate and amount must be checked in comparison with the transfer and store rates. To store binary raw data safely, journaling file systems are preferably used with redundant disks (RAID) or mirroring mechanism, such as “rsync”. A proper choice of the data compression method not only reduces the storage size but also improves the I/O throughputs. DBMS is even applicable to quick search or security around the table data.

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It is observed that electron-beam holes in phase-space evolve dynamically from arising to collapsing in electron time scales in an electron-beam-plasma system. The holes are synchronized with a wave packet dominated by a beam mode of the two-stream instability, and their velocity radii depend on the amplitudes of the packet crests. This shows that the holes are induced by the self-trapping of the beam. The observed images indicate that the holes keep alive due to the hard detrapping of the beam during the packet linear growth, but begin to collapse due to the easy detrapping in the packet saturation.

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