Showing papers by "V. Igochine published in 2004"
TL;DR: In this paper, the motional Stark effect polarization angles of tokamak discharges with current holes are reproduced by a numerical fit of various equilibrium parameters including pressure profile, rotational transform profile and poloidal coil currents.
Abstract: In this paper, we present numerical tools convenient for the investigation of tokamak discharges with current holes. These tools allow the computation of fixed- and free-boundary equilibria with current holes, their representation in Boozer co-ordinates, the determination of the corresponding magnetic fields, field line tracing and also tracing of guiding centre orbits inside the hole. The numerical methods are tested by using two example configurations with different hole sizes. Furthermore, an equilibrium reconstruction of an ASDEX Upgrade discharge is performed. The motional Stark effect polarization angles of this discharge, which indicate a small current hole in the plasma centre, are reproduced by a numerical fit of various equilibrium parameters including pressure profile, rotational transform profile and poloidal coil currents. The resulting plasma parameters lie well inside the experimental error margins.
13 citations
TL;DR: In this article, the authors investigated the role of turbulence suppression mechanisms in the formation of the internal transport barrier (ITB) in ASDEX upgrade discharges and found that the E × B shearing rate was not greater than, or comparable with, the maximum linear growth rate.
Abstract: Advanced tokamak discharges on ASDEX Upgrade can generate an internal transport barrier (ITB) during the current ramp-up phase early in the discharge. Formation of the ITB has become more reliable with the discovery that a low density is necessary for it to form. These ITBs form in very low or negative central shear regions. There is no clear evidence of integer q magnetic surfaces triggering the ITB phase. The appearance of an integer q surface (usually q = 2) often leads to a second ITB (i.e. another steepening in the ion temperature gradient) inside the first ITB.Investigation of possible turbulence suppression mechanisms suggests that something is missing from the generally accepted model of sufficient E × B sheared flow suppressing the turbulence since the E × B shearing rate was not greater than, or comparable with, the maximum linear growth rate in about half of the ITB discharges analysed. Thus, it does not explain the reduced radial transport observed in these discharges.
11 citations