Return To: Session OV2 - Magnetic Fusion Overview 2
Prev Page: Session OV2 - Magnetic Fusion Overview 2
Next Page: (OV2/2) Overview of Alcator C-Mod Recent Results

(OV2/1) Overview on ASDEX Upgrade Results

O. Gruber¹⁾, ASDEX Upgrade Team
 
¹⁾ Max-Planck-Institut für Plasmaphysik, EURATOM-IPP Assoc., 85748 Garching, Germany

Abstract.  Ion and electron temperatures in conventional H mode on ASDEX Upgrade are stiff and limited by a critical temperature gradient length $\Delta$T/T as given by ion temperature gradient (ITG) driven turbulence. ECRH experiments indicate that T_e profiles are also stiff as predicted by ETG turbulence with streamers. Accordingly, core and edge temperatures are proportional to each other and plasma energy is proprtional to pedestal pressure for fixed density profiles. Density profiles are not stiff, and confinement improves with density peaking. Higher triangular shapes ( $\delta$ < 0.45) show strongly improved confinement up to Greenwald density n_GW due to increasing pedestal pressure, and H-mode density operation extends above n_GW. Density peaking at n_GW was achieved with controlled gas puff rates and first results from higher high field side pellet velocities are promising. At n_GW small type II ELMs provide good confinement with low divertor power loading. In advanced scenarios highest performance was achieved in improved H-modes with H_{L - 89P}$\beta_{\mathrm{N}}^{}$ $\approx$ 7.2 at $\delta$ = 0.3, limited by neo-classical tearing modes (NTM) at low central shear ( q_min $\approx$ 1). The T profiles are still governed by ITG/TEM turbulence and confinement is improved by density peaking. Ion internal transport barriers (ITB) discharges with reversed shear and L-mode edge are limited to $\beta_{\mathrm{N}}^{}$ $\leq$ 1.7 by ideal MHD modes and got H_{L - 89P} $\leq$ 2.1. Turbulent transport is suppressed in agreement with ExB shear flow paradigm, and transport coefficients are at neo-classical ion transport level. Reactor-relevant ion and electron ITBs with T_e $\approx$ T_i $\approx$ 10keV were achieved by combining ion and electron heating (NI, ECRH). Full non-inductive current drive was achieved in integrated high preformance H-mode scenario with $\bar{n}_{e}^{}$ = n_GW, $\beta_{\mathrm{p}}^{}$ = 3.1 and H_{L - 89P} = 1.8, which developed ITBs with q_min $\approx$ 1. Central co-ECCD at low densities allowed high current drive fraction of > 80%, while counter-ECCD leads to negative central shear and electron ITB with T_e(0) > 10 keV. MHD phenomena, especially fishbones, contribute to achieve quasi-stationary advanced discharge conditions and trigger ITBs,. but also limit the operation of conventional and advanced scenarios. Complete NTM stabilisation has been demonstrated using ECCD with 10% of heating power. Extension of MHD limits is expected from using off-axis CD (tangential NI) and wall stabilisation. Presently, divertor shape is adapted to higher $\delta$'s and tungsten covering of first wall is extended based on the positive experience using tungsten on divertor and heat shield tiles.

Read the full paper in PDF format.