Influence of the Static Dynamic Ergodic Divertor on Edge Turbulence Properties in TEXTOR

Systematic measurements on the edge turbulence and turbulent transport have been made by Langmuir probe arrays on TEXTOR under various static Dynamic Ergodic Divertor (DED) configurations. Common features are observed. With the DED, in the ergodic zone the local turbulent flux reverses sign from radially outwards to inwards. The turbulence properties are profoundly modified by energy redistribution in frequency spectra and suppression of large scale eddies. The fluctuation poloidal phase velocity changes direction from electron to ion diamagnetic drift, consistent with the observed reversal of the $E_r\times B$ flow. In the laminar region, the turbulence is found to react to an observed reduced flow shear.

Figure 1

Radial profiles of the edge plasma parameters before (black curves) and during (red or gray curves) the static DED measured by fast reciprocating Langmuir probe arrays in an $m/n=6/2$ DED discharge on TEXTOR (No. 99626). (a) Electron temperature; (b) plasma density; (c) electron pressure; (d) radial electric field. The vertical solid line indicates the limiter position ($a\approx 45.7\mathrm{cm}$). The vertical dashed line roughly separates the ergodic (left side) and the laminar (right side) zones.

Figure 2

Time traces of (a) DED currents in coil 1 (thick line) and coil 5 (thin line); (b) power of density fluctuations; (c) power of ${\tilde{E}}_{\theta }$ fluctuations; and (d) ensemble-average of fluctuation-driven particle flux, $⟨{\Gamma }_{\mathrm{fl}}⟩$, measured by a stationary triple probe in the ergodic region ($r\approx 43\mathrm{cm}$) of $m/n=12/4$ static DED. The dotted lines denote the start time of DED.

Figure 3

Radial profiles of fluctuation-driven particle flux $⟨{\Gamma }_{\mathrm{fl}}⟩$ measured by a fast reciprocating triple probe array before (crosses) and during (open circles) the static (a) $m/n=6/2$ and (b) $m/n=3/1$ DED phases. The radial locations are normalized by $a$. The vertical dashed line separates the ergodic (left side) and laminar (right side) zones.

Figure 4

(a) Linear plot of the frequency spectrum $S(f)$ of density fluctuations; (b) semilog plot of the poloidal wave-number spectrum $S(k_{\theta })$ of potential fluctuations measured in the ergodic zone ($r=42.6\mathrm{cm}$) before (black curves) and during (red or gray curves) the static $m/n=6/2$ DED. The inset in (a) shows the log-log plot of $S(f)$ and in (b) the linear plot of $S(k_{\theta })$ normalized by the total values before and during the DED.

Figure 5

Radial profiles of (a) the radial and (b) poloidal correlation lengths measured before (solid circles) and during (open triangles) the static $m/n=6/2$ DED. The vertical solid line indicates the limiter position and the dashed line separates the ergodic (left side) and laminar (right side) zones.

Figure 6

Radial profiles of the poloidal phase velocity of fluctuations, $V_{\mathrm{ph}}$ (symbols), and the $E_r\times B$ drift velocity, $V_{E\times B}$ (curves), before and during the static $m/n=6/2$ DED. The ${\omega }_{*,i}$ (${\omega }_{*,e}$) denotes the ion (electron) diamagnetic drift direction.