The behaviour of the velocity and pressure fluctuations in the outer layers of wall-bounded turbulent flows is analysed by comparing a new simulation of the zero-pressure-gradient boundary layer with older simulations of channels. The 99 % boundary-layer thickness is used as a reasonable analogue of the channel half-width, but the two flows are found to be too different for the analogy to be complete. In agreement with previous results, it is found that the fluctuations of the transverse velocities and of the pressure are stronger in the boundary layer, and this is traced to the pressure fluctuations induced in the outer intermittent layer by the differences between the potential and rotational flow regions. The same effect is also shown to be responsible for the stronger wake component of the mean velocity profile in external flows, whose increased energy production is the ultimate reason for the stronger fluctuations. Contrary to some previous results by our group, and by others, the streamwise velocity fluctuations are also found to be higher in boundary layers, although the effect is weaker. Within the limitations of the non-parallel nature of the boundary layer, the wall-parallel scales of all the fluctuations are similar in both the flows, suggesting that the scale-selection mechanism resides just below the intermittent region, y/S =0.3-0.5. This is also the location of the largest differences in the intensities, although the limited Reynolds number of the boundary-layer simulation (Reg «2000) prevents firm conclusions on the scaling of this location. The statistics of the new boundary layer are available from http://torroja.dmt.upm.es/ftp/blayers/.

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To reveal the scale dependence of the transport of turbulent kinetic energy in a channel flow, the constituents of a spectral energy budget equation are evaluated using direct numerical simulations. At each height in the buffer and overlap layers, the upward turbulent transport provides energy to the fluctuations at small scales, but removes it from those at large scales. Energy removed from the large scales in the overlap layer is carried upward to the centre of the channel and also downward to the vicinity of the wall. The downward energy fluxes at the large scales result in the well-known anomaly of turbulence intensity and the constituents of the budget equation near the wall. In the overlap layer the cospectrum of the spatial turbulent transport is scaled well by the mixing length. It shows that the structure of fluctuations involved in turbulent transport is self-similar in this layer, supporting the classical assumption. The cospectra of pressure–strain correlations are also evaluated. They are not scaled by the wall unit near the wall, but no symptom of the influence of large-scale structures is observed in the cospectra, at least for the present range of Reynolds numbers. Above the buffer layer the cospectra of the pressure–strain correlations are almost isotropic, and their relevant length scale is given by the mixing length in the overlap layer. The pressure–strain correlations are therefore rather local quantities.

The central electron temperature has successfully reached up to 7.5 keV in Large Helical Device (LHD) plasmas with a central high-ion temperature of 5 keV and central electron density of 1.3 × 10 19 m −3 . The result was obtained by heating with a newly-installed 154 GHz gyrotron and also optimization of injection geometry in electron cyclotron heating (ECH). The optimization has been carried out by using the ray-tracing code "LHDGauss," which has been upgraded to include the rapid post-processing three-dimensional (3D) equilibrium mapping obtained from experiments. For ray-tracing calculations, LHDGauss can automatically read the relevant data registered in the LHD database after a discharge, such as ECH injection settings (e.g., Gaussian beam parameters, target positions, polarization, and ECH power) and Thomson scattering diagnostic data along with the 3D equilibrium mapping data. The equilibrium map of the electron density and temperature profiles is then extrapolated into the region outside of the last closed flux surface. Mode purity, or the ratio between the ordinary mode and the extraordinary mode, is obtained by calculating the 1D full-wave equation along the direction of the rays from the antenna to the absorption target point. Using the virtual magnetic flux surfaces, the effects of the modeled density profiles and the magnetic shear at the peripheral region with a given polarization are taken into account. Power deposition profiles calculated for each Thomson scattering measurement timing are registered in the LHD database. Adjustment of the injection settings for the desired deposition profile from feedback provided on a shot-by-shot basis has resulted in an effective experimental procedure.

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The length scales of the spectra and correlation functions of the velocity fluctuations in the overlap region of turbulent wall-bounded flows are analyzed. It is found that a mixing length based on the mean local shear works better as a normalization than the distance to the wall. To define an overlap range sufficiently long and independent of the Reynolds number to allow the two scalings to be tested, the classical asymptotic expansion of the mean shear is extended to include a near-wall virtual origin and a wake component. The result represents well the velocity profile in y+ > 70 and y/δ < 0.3 – 0.5 for Reτ≿2000, and the spectral scales for Reτ≿500. It is suggested that the scaling with a local mixing length could be interpreted as an indication that the size of the eddies is more related to the local shear time scale than to the interaction with the wall. It is also noted that the linearity of the mixing length is a more robust indicator of a logarithmic regime than those that rely on a zero virtual origin.

Enhancement of the output power per gyrotron has been planned in the Large Helical Device (LHD). Three 77-GHz gyrotrons with an output power of more than 1 MW have been operated. In addition, a high power gyrotron with the frequency of 154 GHz (1 MW/5 s, 0.5 MW/CW) was newly installed in 2012, and the total injection power of Electron cyclotron resonance heating (ECRH) reached 4.6 MW. The operational regime of ECRH plasma on the LHD has been extended due to the upgraded ECRH system such as the central electron temperature of 13.5 keV with the line-averaged electron density ne_fir = 1 × 1019 m−3. The electron thermal confinement clearly improved inside the electron internal transport barrier, and the electron thermal diffusivity reached neoclassical level. The global energy confinement time increased with increase of ne_fir. The plasma stored energy of 530 kJ with ne_fir = 3.2 × 1019 m−3, which is 1.7 times larger than the previous record in the ECRH plasma in the LHD, has been successfully achieved.

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