Suppression of Trapped Energetic Ions Driven Resistive Interchange Modes with Electron Cyclotron Heating in a Helical Plasma.

The resistive interchange mode destabilized by the resonant interaction with the trapped energetic ions is fully suppressed when the injected power of electron cyclotron heating exceeds a certain threshold. It is shown for the first time that the complete stabilization of the energetic-particle-driven mode without relaxing the energetic particle (EP) pressure gradient is possible by reducing the radial width of the eigenmodes δ_{w}, especially when δ_{w} narrows to a small enough value relative to the finite orbit width of EP.

Strong Destabilization of Stable Modes with a Half-Frequency Associated with Chirping Geodesic Acoustic Modes in the Large Helical Device.

Abrupt and strong excitation of a mode has been observed when the frequency of a chirping energetic-particle driven geodesic acoustic mode (EGAM) reaches twice the geodesic acoustic mode (GAM) frequency. The frequency of the secondary mode is the GAM frequency, which is a half-frequency of the primary EGAM. Based on the analysis of spatial structures, the secondary mode is identified as a GAM. The phase relation between the secondary mode and the primary EGAM is locked, and the evolution of the growth rate of the secondary mode indicates nonlinear excitation. The results suggest that the primary mode (EGAM) contributes to nonlinear destabilization of a subcritical mode.

Resistive interchange modes destabilized by helically trapped energetic ions in a helical plasma.

A new bursting m=1/n=1 instability (m,n: poloidal and toroidal mode numbers) with rapid frequency chirping down has been observed for the first time in a helical plasma with intense perpendicular neutral beam injection. This is destabilized in the plasma peripheral region by resonant interaction between helically trapped energetic ions and the resistive interchange mode. A large radial electric field is induced near the edge due to enhanced radial transport of the trapped energetic ions by the mode, and leads to clear change in toroidal plasma flow, suppression of microturbulence, and triggering an improvement of bulk plasma confinement.

Fast ion charge exchange spectroscopy adapted for tangential viewing geometry in LHD.

A tangential Fast Ion Charge eXchange Spectroscopy is newly applied on a Large Helical Device (LHD) for co/countercirculating fast ions, which are produced by high energy tangential negative-ion based neutral beam injection. With this new observation geometry, both the tangential-neutral beam (NB) and a low-energy radial-NB based on positive ions can be utilized as probe beams of the measurement. We have successfully observed Doppler-shifted H-alpha lights due to the charge exchange process between the probing NB and circulating hydrogen ions of around 100 keV in LHD plasmas.

Potential measurements with heavy ion beam probe system on LHD.

The heavy ion beam probe system in the Large Helical Device (LHD) was improved as follows. At first, the additional new sweeper was installed into the diagnostic port to extend the observable region. By using this sweeper, the potential profile was measured in a wider minor radius range than in previous experiments, in the case of outward shifted magnetic configuration of LHD. Next, the real time control system was installed to control the probe beam orbit for measuring the potential in plasma with large plasma current. In this system, a digital signal processor was used to control the probe beam in real time. The system worked well in the fixed position observation mode. In the sweeping mode for profile measurement, this control system became unstable. The details of this system and the experimental results are reported in this article.

Observation of reversed-shear Alfvén eigenmodes excited by energetic ions in a helical plasma.

Reversed-shear Alfvén eigenmodes were observed for the first time in a helical plasma having negative q0'' (the curvature of the safety factor q at the zero shear layer). The frequency is swept downward and upward sequentially via the time variation in the maximum of q. The eigenmodes calculated by ideal MHD theory are consistent with the experimental data. The frequency sweeping is mainly determined by the effects of energetic ions and the bulk pressure gradient. Coupling of reversed-shear Alfvén eigenmodes with energetic ion driven geodesic acoustic modes generates a multitude of frequency-sweeping modes.

Change of zonal flow spectra in the JIPP T-IIU tokamak plasmas.

When Ohmically heated low-density plasmas are additionally heated by higher-harmonics ion-cyclotron-range-of frequency heating, heated by neutral beam injection, or strongly gas puffed, the intensity of zonal flows in the geodesic acoustic mode frequency range in the tokamak core plasma decreases sharply and that of low-frequency zonal flow grows drastically. This is accompanied by a damping of the drift wave propagating in the electron diamagnetic drift direction, turbulence by trapped electron mode (TEM), and the increase of the mode propagating to ion diamagnetic drift direction (ITG). In the half-radius region, TEM and high-frequency zonal flows remain intense in both OH and heated phases. ITG and low-frequency zonal flows grow in heated plasmas, suggesting a strong coupling between ITG and low-frequency zonal flow.

Experimental evidence of a zonal magnetic field in a toroidal plasma.

A zonal magnetic field is found in a toroidal plasma. The magnetic field has a symmetric bandlike structure, which is uniform in the toroidal and poloidal directions and varies radially with a finite wavelength of mesoscale, which is analogous to zonal flows. A time-dependent bicoherence analysis reveals that the magnetic field should be generated by the background plasma turbulence. The discovery is classified as a new kind of phenomenon of structured magnetic field generation, giving insight into phenomena such as dipole field generation in rotational planets.

Streamers in the JIPP T-llU tokamak plasmas.

It is shown that the low-density Ohmically heated tokamak plasmas have streamerlike eddies at the outer region at normalized minor radius of about 0.7 and high-frequency zonal flows of large amplitudes in the core. The amplitudes of the eddies ePhi/kT(e) and n(e)/n(e) are of order of 0.5, similar to that of blobs in the tokamak plasma boundary. The waveforms are featured by pulses of complex shape with sharp fronts, similar to the results of streamer simulations by Garbet et al.. The time constant of the fronts is also in agreement with the simulation. The radial span of the eddies is estimated to be much larger than the poloidal span.

Excitation of toroidicity-induced Alfvén eigenmodes by the electrodes inserted in a heliotron/torsatron plasma.

A novel method of exciting shear Alfvén waves using electrodes inserted in a plasma was developed for basic study of Alfvén eigenmodes in a heliotron/torsatron plasma. The electrodes can induce excitation current along the confinement field line, and generate magnetic perturbations perpendicular to the confinement field. By sweeping the frequency of the current in a cold plasma, the toroidicity-induced Alfvén eigenmode was resonantly excited at the predicted frequency and radial location. Plasma response to the applied magnetic perturbations indicates a fairly large damping rate caused by continuum damping.

Identification of zonal flows in a toroidal plasma.

This Letter presents experimental confirmation of the presence of zonal flows in magnetically confined toroidal plasma using an advanced diagnostic system--dual heavy ion beam probes. The simultaneous observation of an electric field at two distant toroidal locations (approximately 1.5 m apart) in the high temperature (approximately 1 keV) plasma provides a fluctuation spectrum of electric field (or flow), a spatiotemporal structure of the zonal flows (characteristic radial length of approximately 1.5 cm and lifetime of approximately 1.5 ms), their long-range correlation with toroidal symmetry (n=0), and the difference in the zonal flow amplitude with and without a transport barrier. These constitute essential elements of turbulence-zonal flow systems, and illustrate one of the fundamental processes of structure formation in nature.

Observation of helicity-induced Alfvén eigenmodes in large-helical-device plasmas heated by neutral-beam injection.

The helicity-induced Alfvén eigenmodes (HAEs) with the toroidal mode number n=2 and 3 are observed for the first time in the Large Helical Device plasmas heated by neutral beam injection. The observed mode frequency is about 8 times higher than that of the observed toroidicity-induced Alfvén eigenmodes, and is proportional to the Alfvén velocity. The modes are excited when the ratio of the beam velocity to the Alfvén velocity exceeds about unity. The frequency lies just above the lower bound of the HAE gap in the plasma edge region of rho>0.7 (rho: normalized minor radius).

Inward turbulent transport produced by positively sheared radial electric field in stellarators.

Inward turbulent particle transport observed in the rf heated plasma of the H-1 toroidal heliac is reproduced in the CHS heliotron/torsatron by generating a region of positive radial electric field shear (E'(r)>0) using electron cyclotron resonance heating of the plasma edge. Empirical condition of the radial reversal of the turbulent flux derived from two experiments indicates that the shear electric field might be universally responsible for the recorrelation of the density and plasma potential fluctuations leading to the inward transport.

Columbin isolated from calumbae radix affects the sleeping time of anesthetized mice.

In a screening series of bioactive components in edible and medicinal plants, we found that Calumbae Radix (Colombo root, 1% powdered feed, for 5 d) and its component, columbin (20-40 mg/kg/d, for 5 d, orally), shortened the sleeping time induced by a urethane and alpha-chloralose mixture and prolonged the sleeping time induced by hexobarbital in mice.

Epidemiology of abomasal nematodes of dairy cattle in Hokkaido, northern Japan.

The prevalence and intensity of infection with abomasal nematodiasis was studied in dairy cattle of Hokkaido, northern Japan, for successive two years. During the period of March in 1985 to September in 1987, a total number of 393 abomasa of Holstein-Friesian cows was examined for nematode parasites. Nematodes were detected from 75% of the cows. The prevalence of nematode species detected was Ostertagia ostertagi 250 (63.6%), Mecistocirrus digitatus 181 (46.1%), Trichostrongylus axei 85 (21.6%) and Haemonchus sp. 1 (0.3%). The prevalence and population composition of each growth stage varied seasonally in O. ostertagi and M. digitatus. The large percentage of arrested larvae, early L4 O. ostertagi and immature L5 M. digitatus, detected during the mid-winter and the increasing percentage of matured adult populations of both species in early spring revealed the occurrence of the autumn associated arrested development (hypobiosis) phenomenon in bovine abomasum nematodes of Japan.

N-(cyclohexylcarbonyl)-D-phenylalanines and related compounds. A new class of oral hypoglycemic agents. 2.

A series of analogues of N-(cyclohexylcarbonyl)-D-phenylalanine (5) have been synthesized and evaluated for their hypoglycemic activity. Relationships were studied between the activity and the three-dimensional structure of the acyl moiety, which was characterized by high-resolution 1H NMR spectroscopy and MNDO calculations. The role of the carboxyl group of the phenylalanine moiety was also studied by comparing the activities of the enantiomers, the decarboxyl derivative, the esters, and the amides of the phenylalanine derivatives. Thus, the structural requirements for possessing hypoglycemic activity was elucidated and a highly active compound, N-[(trans-4-isopropylcyclohexyl)carbonyl]-D-phenylalanine (13) was obtained, which showed a 20% blood glucose decrease at an oral dose of 1.6 mg/kg in fasted normal mice.

N-acylphenylalanines and related compounds. A new class of oral hypoglycemic agents.

N-Benzoyl-DL-phenylalanine (1) was found to possess hypoglycemic activity. A series of the analogues of compound 1 were prepared and evaluated for their blood glucose lowering activity. Both the steric effects of the phenylalanine moiety and the effects of variations in the acyl moiety were investigated. This study elucidated some of the structure-activity relationships and led to the development of N-(4-ethylbenzoyl)-D-phenylalanine (34), which was 50 times more potent than the initial compound 1.