Satoru Kiyama

Design concept and confinement prediction of TPE-RX reversed-field pinch device

Abstract TPE-RX is a large-sized reversed-field pinch machine newly constructed at the Electrotechnical Laboratory. In this paper the design concepts, procedures to determine the machine size and the flux swing to drive the plasma current, and the prediction of the global confinement properties of the TPE-RX are reported. From these considerations, major and minor radii (R, a) are decided to be R/a=1.7175/0.45 m, respectively. It is estimated that the flux swing of the iron core of more than 3.9 Wb is necessary to drive 1 MA of plasma current, Ip, which is the given constraint of the machine. Energy confinement time in the range of 3–18 ms is predicted to be attained at Ip=1 MA depending on the models and assumptions.

Front-end system of the TPE-RX reversed-field pinch machine

Key design points of the front-end system of TPE-RX reversed-field pinch (RFP) machine are described. Here the front-end system is the components of the machine between the thick shell and the plasma surface and it consists of the vacuum vessel, shell system and pulsed vertical field coil (PVC). The effect of the multi-layered shell system is examined in terms of the relative radial magnetic perturbation. A summary of the port error field and the magnetic field produced by the PVC are also shown. The actual construction procedure is also described. Construction of the TPE-RX was completed at the end of December 1997 and it is now routinely in operation with RFP configuration.

On the statistics of edge fluctuations: comparative study between various fusion devices

In this paper we present a statistical study of edge fluctuations taken with the gas puffing imaging (GPI) diagnostics. We carry out a comparison of GPI signal from an extensive database including four devices (two tokamaks and two reversed field pinches). The data are analysed in terms of their statistical moments Skewness and Kurtosis, as done in B Labit et al (2007 Phys. Rev. Lett. 98 255002). The data align along parabolic curves, although different from machine to machine, with some spread around the best-fitting curve. A discussion about the meaning of the parabolic trend as well as the departure of real data from it is provided. A phenomenological model is finally provided, attempting to accommodate experimental evidence.

Extensive magnetic measurement system for TPE-RX

Abstract An extensive magnetic measurement system (MMS) which contains 1201 sensors is developed for the new large reversed-field pinch machine, TPE-RX. The system facilitates a variety of magnetic signals for axisymmetric information to obtain equilibrium profiles as well as for nonaxisymmetric information of the magnetic perturbation mode spectra. The system is now routinely in operation for physics experiments on TPE-RX. The physical quantities obtained from the system, locations and specifications of coils and loops, calibration, the method of managing large amounts of data and examples of data are reported.

The first results of TPE-RX, a large reversed-field pinch machine

The first experimental results of a large reversed-field pinch machine, TPE-RX, are reported. A reversed-field pinch configuration in TPE-RX was successfully obtained in March 1998. The highest plasma current, Ip, of 480 kA and the longest pulse duration time of 70 ms have so far been obtained separately. A minimum loop voltage of about 15 V is obtained at Ip=150-250 kA. A locked mode has been found to exist in TPE-RX from the magnetic and vessel-temperature measurements, while the C++ Doppler spectrum shows a finite toroidal rotation.

Spectroscopy of reactive species produced by low-energy atmospheric-pressure plasma on conductive target material surface

A method for blood coagulation using low-energy atmospheric-pressure plasma (LEAPP) is confirmed as an alternative procedure to reduce tissue damage caused by heat. Blood coagulation using LEAPP behaves differently depending on working gas species; helium is more effective than argon in promoting fast coagulation. To analyse the difference in reactive species produced by helium and argon plasma, spectroscopic measurements were conducted without and with a target material. To compare emissions, blood coagulation experiments using LEAPP for both plasmas were performed under almost identical conditions. Although many kinds of reactive species such as hydroxyl radicals and excited nitrogen molecules were observed with similar intensity in both plasmas, intensities of nitrogen ion molecules and nitric oxide molecules were extremely strong in the helium plasma. It is considered that nitrogen ion molecules were mainly produced by penning ionization by helium metastable. Near the target, a significant increase in the emissions of reactive species is observed. There is a possibility that electron acceleration was induced in a local electric field formed on the surface. However, in argon plasma, emissions from nitrogen ion were not measured even near the target surface. These differences between the two plasmas may be producing the difference in blood coagulation behaviour. To control the surrounding gas of the plasma, a gas-component-controllable chamber was assembled. Filling the chamber with O2/He or N2/He gas mixtures selectively produces either reactive oxygen species or reactive nitrogen species. Through selective treatments, this chamber would be useful in studying the effects of specific reactive species on blood coagulation.

Quasi-single helicity state at shallow reversal in TPE-RX reversed-field pinch experiment

The operating conditions for obtaining a quasi-single helicity (QSH) state with a good reproducibility are found in a reversed-field pinch (RFP) experiment on the large RFP machine, TPE-RX [Y. Yagi et al., Fusion Eng. Des. 45, 421 (1999)]. In these conditions, the reversal of toroidal magnetic field (Bta) is maintained at a very shallow value (∼−0.2mT) after the setting up phase and the following fast current rising phase. After a certain period at this shallow reversal (∼15–25ms), the m∕n=1∕6 mode (m and n being the poloidal and toroidal Fourier mode numbers, respectively) rapidly grows and saturates before the termination of discharge. The growth of this mode dominates the other modes and the QSH state with m∕n=1∕6 is finally achieved. This QSH state can be sustained for a long period (up to ∼45ms) almost until the end of discharge by applying a delayed reversal of Bta with appropriate trigger timing and magnitude. The initial setup of the QSH states shows a reproducibility of almost 100%, but its susta...

Development of Ion Beam Sources with Wide Beam Energy and Current Ranges

Using a neutral beam injection system with large electrodes for a nuclear fusion device, high currents of nitrogen ion (N+) beams with energies of 300 V are successfully extracted for plasma application. In an acceleration with a low energy of 300 V, a N+ beam current (~9 mA/cm2) on the ampere order is achieved without the optimization of extraction aperture diameter, electrode thickness and the distance between the electrodes. Main beam elements are confirmed as N+ particles using a mass spectrometer. In this system, concave electrodes with an effective diameter of 345 mm are adopted to focus the beams. Therefore, we can obtain a high current density and high-flux ion beam at the focal point. In an acceleration with a high energy of ~23 kV, a N+ beam with a current density of ~456 mA/cm2 and a flux of ~3.1×1022 m-2 s-1 is irradiated onto an aluminum material, then surface modification is confirmed.

Observations of multiple stationary striation phenomena in an atmospheric pressure neon plasma jet

The formation of multiple stationary striations between a nozzle exit and a conductive target plate was clearly observed at regular intervals using a digital camera along an atmospheric pressure plasma jet of dielectric barrier discharge using a neon gas into ambient air. From the results of measuring using a high-speed camera during the positive current phase, the emission initially started in the middle between the nozzle and the target, and striations progressed in both upward and downward directions. During the negative current phase, the emission initially started in a region near the target, and the striations rapidly progressed to the nozzle.

Electrostatic turbulence in the edge of TPE-RX and driving mechanisms

In order to understand the driving mechanisms that underlie the turbulence in the plasma edge of fusion devices, contemporary measurements of light emission fluctuations with the gas puff imaging diagnostic and of the electrostatic potential with Langmuir probes are carried out in the TPE-RX plasma device. The analysis made with the conditional average technique demonstrates a clear link between the two types of structures, with a phase shift of ?/2. This relation suggests that the curvature driven modes are a possible source of free energy for edge turbulence in this machine, as similarly found in other plasma devices.