52nd Annual Meeting of the APS Division of Plasma Physics
Volume 55, Number 15
Monday–Friday, November 8–12, 2010;
Chicago, Illinois
Session BI3: 3D Fields and Effects
9:30 AM–12:30 PM,
Monday, November 8, 2010
Room: Grand Ballroom EF
Chair: Brett Chapman, University of Wisconsin
Abstract ID: BAPS.2010.DPP.BI3.3
Abstract: BI3.00003 : Three-dimensional equilibria and transport in RFX-mod: a description using stellarator tools
10:30 AM–11:00 AM
Preview Abstract
Abstract
Author:
Marco Gobbin
(Consorzio RFX, Associazione Euratom-ENEA sulla fusione, Padova, Italy)
RFX-mod self-organized Single Helical Axis (SHAx) states, spontaneously
obtained at high plasma current up to 2 MA, provide a unique opportunity to
advance 3D fusion physics and establish a common knowledge basis in a
parameter region not covered by Stellarator and Tokamak. VMEC code was
adapted to reversed-field pinch (RFP) to model SHAx equilibria, which have a
helical core embedded in an almost axisymmetric boundary. Feedback control
of helical magnetic field reinforces persistency of 3D shaping, which also
increases with plasma current. The helical region boundary, corresponding to
an electron transport barrier with zero magnetic shear, high flow shear and
improved confinement, is investigated using numerical codes common to the
stellarator community. The experimental electron heat diffusivity ($\approx
10m^2/s$ at the barrier), computed by the ASTRA code in 3D coordinates,
decreases with plasma current and corresponding residual chaos reduction.
The averaged particle diffusivity $\bar {D}$ over the helical volume,
estimated with the Monte-Carlo code ORBIT, is consistent with experiment and
increases with collisionality. $\bar {D}$ does not show the $1/\nu $ trend of
un-optimized stellarators because of de-trapping mechanisms and the absence
of superbananas due to negligible helical ripple in the edge. Furthermore,
DKES code is being adapted to RFP for local neoclassical transport
computations, including radial electric field, in order to estimate
diffusion coefficients in the barrier region for typical RFX-mod temperature
and density profiles. No change of impurity transport is found, which is
consistent with fully collisional transport, and experimentally with a
hollow impurity profile and edge-peaked radiation measurements, as in LHD.
Analytical and numerical tools like GS2 indicate that small-scale turbulence
contributes to drive anomalous transport in the barrier region. Thermal
conductivity estimated from microtearing modes is consistent with
experiment.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2010.DPP.BI3.3