In magnetic fusion plasmas, a transport barrier is essential to improve the plasma confinement. The key physics behind the formation of a transport barrier is the suppression of the micro-scale ...turbulent transport. On the other hand, long-range transport events, such as avalanches, has been recognized to play significant roles for global profile formations. In this study, we observed the impact of the avalanche-type of transport on the formation of a transport barrier for the first time. The avalanches are found to inhibit the formation of the internal transport barrier (ITB) observed in JT-60U tokamak. We found that (1) ITBs do not form in the presence of avalanches but form under the disappearance of avalanches, (2) the surface integral of avalanche-driven heat fluxe is comparable to the time rate change of stored energy retained at the ITB onset, (3) the mean E × B flow shear is accelerated via the ion temperature gradient that is not sustained under the existence of avalanches, and (4) after the ITB formation, avalanches are damped inside the ITB, while they remain outside the ITB.
Spatio-temporal structures of ion heat flux and radial electric field are investigated on JT-60U to understand a mechanism of the internal transport barrier (ITB) formation. Contrary to the ...conventional argument that the ITB formation is due to the E×B flow shear suppressions on turbulence, we observe that the E×B shearing rate during the ITB formation is not enough for turbulence suppressions with kρi ∼ 1. Another finding is that the ITB is formed simultaneously with abrupt decreases of ion heat flux in the global region (like the report in Neudatchine et al 1999 Plasma Phys. Control. Fusion 41 L39), and the gradient-flux relations are non-diffusively developed step by step. These observations suggest the importance of the change in the long-radial fluctuations, which is previously observed in JT-60U (Nazikian et al 2005 Phys. Rev. Lett. 94 135002). Therefore, the model of effects by non-uniformity of the radial electric field, under the condition where the scale separation is violated, is employed to explain such fluctuation quenching. Consistent results are obtained showing that the non-uniformity of the radial electric field effectively works on the fluctuations with long-radial wavelength and increases the temperature gradient. It seems natural that the suppression of the long-radial fluctuations drives the global transport improvement to form the ITB.
Abstract
Turbulent transport is undoubtedly important in magnetic confinement plasmas. It has been reported that a lot of transport dynamics are not satisfying the local diffusive models. Here, we ...report the quantitative measurement of electron heat flux associated with ballistic propagating long-range transport events, which is considered to be a component of avalanches. In addition, we show the first observations of the substantial impact of avalanche-driven transport on profile resilience (or profile stiffness) observed in JT-60U. We found that, in the channel of the electron heat flux, the ratio between the increment of the avalanche-driven component to that of the total plasma heating becomes dominant (∼80%) in the case of the high-heating limit. This suggests a possible role for avalanche-driven transport to induce profile resilience, which has been evidenced by flux-driven simulations.
The differences in rorqual feeding ecology have been linked to the presence of different morphological markers. The Antarctic minke whale (Balaenoptera bonaerensis Burmeister, 1867) and the common ...minke whale (Balaenoptera acutorostrata Lacépède, 1804) are closely related species, but their morphological differences have not been fully investigated. In this study, we compared 21 skull and 11 feeding apparatus (baleen and mouth-related parts) measurement points between these two species using hundreds of individuals covering a wide range of body lengths in both sexes. Their engulfment capacities were estimated using these measurements. Our results show that Antarctic minke whales have (i) proportionally larger skulls to the body length, (ii) more dorsoventrally and laterally curved rostra, (iii) proportionally larger feeding apparatuses to the condylobasal length, and (iv) significantly larger engulfment capacity than common minke whales. These differences could indicate that Antarctic minke whales have developed a feeding strategy suitable for feeding on krill, which forms large schools. In contrast, common minke whales have adapted to prey on small pelagic fishes that are agile and form small schools.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Context.
Empirical relations between major UV and extreme UV spectral lines are one of the inputs for models of chromospheric and coronal spectral radiances and irradiances. They are also needed for ...the interpretation of some of the observations of the Solar Orbiter mission.
Aims.
We aim to determine an empirical relation between the intensities of the H
I
121.6 nm and He
II
30.4 nm Ly-
α
lines.
Methods.
Images at 121.6 nm from the Chromospheric Lyman-Alpha Spectro Polarimeter (CLASP) and Multiple XUV Imager (MXUVI) sounding rockets were co-registered with simultaneous images at 30.4 nm from the EIT and AIA orbital telescopes in order to derive a spatially resolved relationship between the intensities.
Results.
We have obtained a relationship between the H
I
121.6 nm and He
II
30.4 nm intensities that is valid for a wide range of solar features, intensities, and activity levels. Additional SUMER data have allowed the derivation of another relation between the H
I
102.5 nm (Ly-
β
) and He
II
30.4 nm lines for quiet-Sun regions. We combined these two relationships to obtain a Ly-
α
/Ly-
β
intensity ratio that is comparable to the few previously published results.
Conclusions.
The relationship between the H
I
121.6 nm and He
II
30.4 nm lines is consistent with the one previously obtained using irradiance data. We have also observed that this relation is stable in time but that its accuracy depends on the spatial resolution of the observations. The derived Ly-
α
/Ly-
β
intensity ratio is also compatible with previous results.
We developed a polarization modulation unit (PMU) to rotate a waveplate continuously in order to observe solar magnetic fields by spectropolarimetry. The non-uniformity of the PMU rotation may cause ...errors in the measurement of the degree of linear polarization (scale error) and its angle (crosstalk between Stokes-
Q
and -
U
), although it does not cause an artificial linear polarization signal (spurious polarization). We rotated a waveplate with the PMU to obtain a polarization modulation curve and estimated the scale error and crosstalk caused by the rotation non-uniformity. The estimated scale error and crosstalk were
<
0.01
%
for both. This PMU will be used as a waveplate motor for the
Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP) rocket experiment. We confirm that the PMU performs and functions sufficiently well for CLASP.
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