Poloidal Rotation Dynamics, Radial Electric Field, and Neoclassical Theory in the Jet Internal-Transport-Barrier Region

Results from the first measurements of a core plasma poloidal rotation velocity ($v_{\theta }$) across internal transport barriers (ITB) on JET are presented. The spatial and temporal evolution of the ITB can be followed along with the $v_{\theta }$ radial profiles, providing a very clear link between the location of the steepest region of the ion temperature gradient and localized spin-up of $v_{\theta }$. The $v_{\theta }$ measurements are an order of magnitude higher than the neoclassical predictions for thermal particles in the ITB region, contrary to the close agreement found between the determined and predicted particle and heat transport coefficients [K.-D. Zastrow et al., Plasma Phys. Controlled Fusion 46, B255 (2004)]. These results have significant implications for the understanding of transport barrier dynamics due to their large impact on the measured radial electric field profile.

Figure 1

Radial $T_i$ profiles during the evolution of the ITB for (a) No. 61352 and (b) No. 58094. The vertical lines show the locations of the CXRS channels for $v_{\theta }$ measurements.

Figure 2

(a) The ITB criterion and the locations of three of the $v_{\theta }$ channels in the region of the steep temperature gradient. (b) Time traces of $v_{\theta }$ at the three different CXRS radii shown in Fig. 2a, with the error bars represented by the dotted curves.

Figure 3

(a) ITB criterion for shot No. 58094 and the locations of the CXRS channels for $v_{\theta }$ measurement. (b) Time traces of $v_{\theta }$ measured at the three different radii shown in Fig. 3a.

Figure 4

Reflectometry measurements of (a) radial position of the cutoff layer for three frequencies, (b) sliding FFT spectrogram of the reflected signal and (c) integrated spectrogram.

Figure 5

(a) and (b) Comparison of measured $v_{\theta }$ profiles with neoclassical predictions for the thermal particles by NCLASS for the two discharges during the ITB. (c) and (d) $E_r$ profiles calculated using Eq. (1), with the measured $v_{\theta }$ values (stars) and the NCLASS $v_{\theta }$ predictions (solid line) and measured toroidal and pressure gradient components.