Development of a tracer-containing compact-toroid injection system.

The accumulation and behavior of impurities is one of the most important subjects in the development of magnetically confined fusion reactors because impurities can potentially cause cooling and worsen the confinement of the hot core plasma. Tracer-encapsulated solid pellets (TESPELs) have demonstrated some results for impurity injection for fusion-reactor plasma studies [N. Tamura , J.

Reconstruction of radiation profiles near the plasma boundary using an infrared imaging video bolometer in KSTAR.

An infrared imaging video bolometer using tomographic inversion can provide the total radiated power and 2-D radiation profiles, which are crucial information for impurity seeding experiments. Because large amounts of impurities exist at the plasma edge, accurate reconstruction of the radiation profiles near the material boundary is an important issue. In this study, two methods of boundary condition treatment are compared.

Initial operation results of NE213 scintillation detector for time-resolved measurements on triton burnup in KSTAR.

In time-resolved measurement for triton burnup in Korea Superconducting Tokamak Advanced Research (KSTAR) deuterium plasmas, an NE213 liquid scintillation detector was installed and operated during the 2017 KSTAR campaign. The detector is composed of an NE213 scintillator (50 mm in diameter and 10 mm in thickness) and a photomultiplier tube (PMT). The PMT anode signal was processed under a data acquisition system which contains a field programmable gate array circuit and pulse processing software that is capable of discriminating gamma-ray and neutron pulse signals.

A heterodyne dispersion interferometer for wide bandwidth density measurements on DIII-D.

In order to improve both the density and particularly the temporal resolution beyond previous dispersion interferometers (DIs), a heterodyne technique based on an acousto-optic (AO) cell has been added to the DI. A 40 MHz drive frequency for the AO cell allows density fluctuation measurements into the MHz range. A CO laser-based heterodyne DI (HDI) installed on DIII-D has demonstrated that the HDI is capable of tracking the density evolution throughout DIII-D discharges, including disruption events and other rapid transient phenomena.

Scintillating fiber detectors for time evolution measurement of the triton burnup on the Large Helical Device.

Two scintillating fiber (Sci-Fi) detectors have been operated in the first deuterium plasma campaign of the Large Helical Device in order to investigate the time evolution of the triton burnup through secondary 14 MeV neutron measurement. Two detectors use scintillating fibers of 1 mm diameter embedded in an aluminum matrix with a length of 10 cm connected to the magnetic field resistant photomultiplier. A detector with 91 fibers was developed in the Los Alamos National Laboratory and has been employed on JT-60U.

Nd:YAG laser Thomson scattering diagnostics for a laboratory magnetosphere.

A new Nd:YAG laser Thomson scattering (TS) system has been developed to explore the mechanism of high-beta plasma formation in the RT-1 device. The TS system is designed to measure electron temperatures (T) from 10 eV to 50 keV and electron densities (n) of more than 1.0 × 10 m.

Development of a high-speed full digital processing phase detector for interferometry.

This study describes the development of a fully digital-type phase detector for plasma interferometry. This detector functions even in situations in which the phase changes rapidly or the input signal is too small to derive the correct phase shift from the intermediate frequency (IF) signal. The detector directly converts the IF signal waveform of the interferometer to the phase shift signal by means of data processing in a logic circuit.

Performance of fast-ion loss diagnostic on EAST.

The scintillator-based detector for fast-ion loss measurements has been installed on EAST. To obtain high temporal resolution for fast-ion loss diagnostics, fast photomultiplier tube systems have been developed which can supply the complementary measurements to the previous image system with good energy and pitch resolution by using a CCD camera. By applying the rotatable platform, the prompt losses of beam-ions can be measured in normal and reverse magnetic field.

Tracer-Encapsulated Solid Pellet (TESPEL) injection system for Wendelstein 7-X.

Impurity confinement in fusion plasmas is mainly determined by transport mechanisms in the core region. For the Wendelstein 7-X stellarator, its island divertor is expected to screen effectively external impurity sources in the scrape-off layer at higher densities. However, the unique feature of Tracer-Encapsulated Solid Pellet (TESPEL) injection, releasing impurities at a well-localized radial position directly in the core plasma, enables investigating such transport mechanisms.

Microwave frequency comb Doppler reflectometer applying fast digital data acquisition system in LHD.

We succeeded in increasing the radial observation points of the microwave frequency comb Doppler reflectometer system from 8 to 20 (or especially up to 45) using the high sampling rate of 40 GS/s digital signal processing. For a new acquisition system, the estimation scheme of the Doppler shifted frequency is constructed and compared with the conventional technique. Also, the fine radial profile of perpendicular velocity is obtained, and it is found that the perpendicular velocity profile is consistent with the × drift velocity one.

Signal to noise ratio of upgraded imaging bolometer for KSTAR.

An InfraRed imaging Video Bolometer (IRVB) was installed on KSTAR in 2012 having a ∼2 m × 7 cm × 9 cm Pt foil blackened with graphite and a 5 mm × 5 mm aperture located 7.65 cm from the foil with 16 × 12 channels and a time resolution of 10 ms. The IR camera was an Indigo Phoenix (InSb, 320 × 256 pixels, 435 fps, <25 mK).

Magnetized fast isochoric laser heating for efficient creation of ultra-high-energy-density states.

Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive and alternative approach to create ultra-high-energy-density states like those found in inertial confinement fusion (ICF) ignition sparks. Laser-produced relativistic electron beam (REB) deposits a part of kinetic energy in the core, and then the heated region becomes the hot spark to trigger the ignition. However, due to the inherent large angular spread of the produced REB, only a small portion of the REB collides with the core.

Simulations tackle abrupt massive migrations of energetic beam ions in a tokamak plasma.

In the late 1990s, fusion scientists at the Japanese tokamak JT-60U discovered abrupt large-amplitude events during beam-driven deuterium plasma experiments. A large spike in the magnetic fluctuation signal followed by a drop in the neutron emission rate indicates that energetic ions abruptly migrate out of the plasma core during an intense burst of Alfvén waves that lasts only 0.3 ms.

Effectiveness of an Imaging Plate System in Emergency 131I Thyroid Monitoring.

The effect of temperature and shielding on the lower detection limit of a thyroid I monitoring system was investigated in an anthropomorphic thyroid-neck phantom fitted with an imaging plate. The phantom was loaded with an I aqueous solution and monitored with the imaging plate for 10 min. After exposure, the plates were incubated with or without the shield at 0, 10, 20, 25, 30, or 40°C.

Hysteresis Relation between Turbulence and Temperature Modulation during the Heat Pulse Propagation into a Magnetic Island in DIII-D.

The hysteresis relation between turbulence and temperature modulation during the heat pulse propagation into a magnetic island is studied for the first time in toroidal plasmas. Lissajous curves of the density fluctuation (n[over ˜]/n) and the electron temperature (T_{e}) modulation show that the (n[over ˜]/n) propagation is faster than the heat pulse propagation near the O point of the magnetic island. This faster n[over ˜]/n propagation is experimental evidence of the turbulence spreading from the X point to the O point of the magnetic island.

Chirping and Sudden Excitation of Energetic-Particle-Driven Geodesic Acoustic Modes in a Large Helical Device Experiment.

Energetic-particle-driven geodesic acoustic modes (EGAMs) observed in a Large Helical Device experiment are investigated using a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic (MHD) fluid. The frequency chirping of the primary mode and the sudden excitation of the half-frequency secondary mode are reproduced for the first time with the hybrid simulation using the realistic physical condition and the three-dimensional equilibrium. Both EGAMs have global spatial profiles which are consistent with the experimental measurements.

Induction of subterahertz surface waves on a metal wire by intense laser interaction with a foil.

We have demonstrated that a pulsed electromagnetic wave (Sommerfeld wave) of subterahertz frequency and 11-MV/m field strength can be induced on a metal wire by the interaction of an intense femtosecond laser pule with an adjacent metal foil at a laser intensity of 8.5×10^{18}W/cm^{2}. The polarity of the electric field of this surface wave is opposite to that obtained by the direct interaction of the laser with the wire.

Dependence of electron impact differential cross sections on the ionic charge to radius ratio for the Al(2p) and Be(1s) ions.

The triple differential cross sections (TDCSs) have been obtained for the electron impact ionization of ionic targets, Al(2p) and Be(1s), having nearly the same ratio of ionic charge to radius. In the first of this kind of study, the trends of cross sections have been found to match to a greater extent despite ionization taking place from the ionic targets having considerable difference in nuclear charges as well as the ionization taking place from different types of orbitals, p-orbital and s-orbital. The trends of TDCSs have not been found to agree considerably for the neutral Al (3p) and Be (2s) targets.

Quantification of Turbulent Driving Forces for the Geodesic Acoustic Mode in the JFT-2M Tokamak.

We investigate spatial structures of turbulence and turbulent transport modulated by the geodesic acoustic mode (GAM), from which the excitation mechanism of the GAM is discussed. The GAM is found to be predominantly excited through a localized Reynolds stress force, rather than the dynamic shearing force. The evaluated growth rate is larger than the linear damping coefficients and is on the same order of magnitude as the effective growth rate evaluated from time evolution in the GAM kinetic energy.

Trigger mechanism for the abrupt loss of energetic ions in magnetically confined plasmas.

Interaction between a quasi-stable stationary MHD mode and a tongue-shaped deformation is observed in the toroidal plasma with energetic particle driven MHD bursts. The quasi-stable stationary 1/1 MHD mode with interchange parity appears near the resonant rational surface of q = 1 between MHD bursts. The tongue-shaped deformation rapidly appears at the non-resonant non-rational surface as a localized large plasma displacement and then collapses (tongue event).

In situ calibration of neutron activation system on the large helical device.

In situ calibration of the neutron activation system on the Large Helical Device (LHD) was performed by using an intense Cf neutron source. To simulate a ring-shaped neutron source, we installed a railway inside the LHD vacuum vessel and made a train loaded with the Cf source run along a typical magnetic axis position. Three activation capsules loaded with thirty pieces of indium foils stacked with total mass of approximately 18 g were prepared.

Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma.

Spatiotemporal evolutions of radial electric field and turbulence are measured simultaneously in the H-mode transition, which is a prototypical example of turbulence structure formation in high-temperature plasmas. In the dynamical phase where transport barrier is established abruptly, the time-space-frequency-resolved turbulent particle flux is obtained. Here we report the validation of the mechanism of transport barrier formation quantitatively.

A new dispersion interferometer on HL-2A.

In order to avoid a fringe jump caused by high plasma density and pellet injection [Y. Zhou et al., Rev.

A motional Stark effect diagnostic analysis routine for improved resolution of iota in the core of the large helical device.

A new Motional Stark Effect (MSE) analysis routine has been developed for improved spatial resolution in the core of the Large Helical Device (LHD). The routine was developed to reduce the dependency of the analysis on the Pfirsch-Schlüter (PS) current in the core. The technique used the change in the polarization angle as a function of flux in order to find the value of diota/dflux at each measurement location.

Development of bolometric tomography technique for high-contrast radiation distribution in toroidal devices.

An extended Computed Tomography (CT) technique with a priori information based on Phillips-Tikhonov regularization has been developed to handle a high-contrast radiation distribution, which can result in large reconstruction errors in the region where radiation intensity is low, with few line of sight (LOS) data. Reference profiles generated from LOS data for every time slice are employed as the a priori information. In the extended technique, the weighting parameter for the reference profile is automatically determined from the LOS data, to avoid an inappropriate reference.