Sheared flows have been experimentally studied in TJ-II plasmas. In lowdensity ECH plasmas, sheared flows can be easily controlled by changing the plasma density, thereby allowing the radial origin and evolution of the edge velocity shear layer to be studied. In high density NBI heated plasmas a negative radial electric field is observed that is dominated by the diamagnetic component. The shear of the negative radial electric field increases at the L-H transition by an amount that depends on the magnetic configuration and heating power. Magnetic configurations with and without a low order rational surface close to the plasma edge show differences that may be interpreted in terms of local changes in the radial electric field induced by the rational surface that could facilitate the L-H transition. Fluctuation measurements show a reduction in the turbulence level that is strongest at the position of maximum E r shear. High temporal and spatial resolution measurements indicate that turbulence reduction precedes the increase in the mean sheared flow, but is simultaneous with the increase in the low frequency oscillating sheared flow. These observations may be interpreted in terms of turbulence suppression by oscillating flows, the so-called zonal flows.

The statistical properties of plasma fluctuations have been investigated in the plasma boundary region of fusion ͑tokamaks and stellarators͒ and nonfusion plasmas. Fluctuations in ion saturation current and floating potential have a near-Gaussian character in the proximity of the velocity shear layer (r sh ). However, fluctuations deviate from a Gaussian distribution when moving inside of the plasma edge (rϽr sh ) or into the scrape-off layer region (rϾr sh ). Furthermore, fluctuations show sporadic pulses that are asymmetric in time. The present analysis shows a coupling of those pulses and the averaged flow in the shear layer region.

As the finalization of the hydrogen experiment towards the deuterium phase, the exploration of the best performance of the hydrogen plasma was intensively performed in the Large Helical Device (LHD). High ion and electron temperatures, Ti, Te, of more than 6 keV were simultaneously achieved by superimposing the high power electron cyclotron resonance heating (ECH) on the neutral beam injection (NBI) heated plasma. Although flattening of the ion temperature profile in the core region was observed during the discharges, one could avoid the degradation by increasing the electron density. Another key parameter to present plasma performance is an averaged beta value . The high regime around 4 % was extended to an order of magnitude lower than the earlier collisional regime. Impurity behaviour in hydrogen discharges with NBI heating was also classified with the wide range of edge plasma parameters. Existence of no impurity accumulation regime where the high performance plasma is maintained with high power heating > 10 MW was identified. Wide parameter scan experiments suggest that the toroidal rotation and the turbulence are the candidates for expelling impurities from the core region.

Transitions to an enhanced confinement regime in tokamak plasmas with negative central magnetic shear have been observed in a number of devices. A simple model incorporating the nonlinear coupling between the turbulent fluctuations and the sheared radial electric field is added to a transport model in order to investigate the dynamics of the transition to this enhanced confinement mode. In this model, by incorporating both the instability growth rate profiles and particle and/or power deposition profiles, a rich variety of transition dynamics is uncovered. Transition dynamics and their concomitant thresholds are examined within the context of these models. In the course of investigating these transitions, potential methods for triggering and controlling these enhanced confinement regimes have been discovered and are discussed.

An inter-machine dataset covering devices of different size and a variety of magnetic configurations is comprehensively analysed to assess the ranges of validity of neoclassical (NC) transport predictions in medium-to high density, high temperature discharges. A recently concluded benchmarking of calculations of transport coefficients from local NC theory [1] allows now a quantitative experimental energy transport study. While in earlier inter-machine studies of NC transport in 3D devices the electron energy transport at low densities has been investigated [2], this study focuses on the energy transport at medium to higher densities as anticipated when approaching reactor conditions. The validation approach as done here is to compare two fluxes: first, the 'NC flux' is determined with the NC transport coefficients and the gradients of the experimental density and temperature profiles. Second, the sources from deposition calculations considering heating and particle sources (the latter where available) yield the 'experimental flux'. Both fluxes are compared and the NC radial electric field E