Particle transport in low core turbulence Tore-Supra plasmas

Abstract

Electron and impurity transport has been studied in sawtoothing plasmas in the Tore-Supra tokamak. High time and space resolution measurements of the electron density reveal the existence of a flat profile region encompassing the q = 1 surface, on which is superimposed a density peak building up between sawtooth relaxations. For the first time in this regime, we have determined the underlying transport of both nickel and electrons independently of the effect of sawteeth in the central part of the plasma. Electron transport is consistent with the neoclassical expectations only in the close vicinity of the magnetic axis. Further out, it exceeds the neoclassical values as calculated with the NCLASS code, although the turbulence level is very low in the whole central region region. In contrast, nickel transport is in good agreement with the neoclassical calculations in the same region. The neoclassical effect on trapped particles of a persisting mode due to incomplete reconnection of the magnetic surfaces is consistent with these observations.

Argon impurity transport studies at Wendelstein 7-X using x-ray imaging spectrometer measurements

“…Alternatively, fluxes and transport coefficients can be derived from the knowledge of total impurity densities, as shown for impurity transport [19][20] and also for electron transport [21], neglecting external sink and source terms. However, for one particular charge state, it is not straight forward to measure transport coefficients and impurity fluxes directly, since e.g.…”

Modification of impurity transport in the presence of saturated (m,n) = (1,1) MHD activity at ASDEX Upgrade

“…The modelled ionization balance and relative emission characteristics (known from atomic data calculations) are then used to evaluate the radiated power so to match the time evolution of experimental spectroscopic signals (see e.g. [10,11,12,13,14,15,16]). Other methods require the experimental determination of the total impurity density profile and its time evolution after the injection.…”

Particle Flow during Sawtooth Reconnection: Numerical Simulations of Experimental Observations

“…5000 profiles were measured in 225 ms covering several sawtooth cycles. This peaking on axis has been shown to be due to the neoclassical Ware pinch and a drop of the particle diffusion [11]. The mexican hat like structure is not seen on the temperature which presents a smooth dome near the axis.…”

“…Closer examination of the blue, red and green profiles on Fig. 4 b) indicates strong flattening over a ring 0.2 m wide in only 10 ms. A diffusive process would require D ⊥ 4 m 2 .s −1 , while it was measured to be of the order of 0.05 m 2 .s −1 in the deep core [11]. Also the flattening would most likely be seen on the temperature as well, but as shown on Fig.…”

“…Figure 4 displays the core density profiles together with the electron temperature measured using electron cyclotron emission, during the same pulse, but 150 ms later (t = 5.15 − 5.17 s). The peaking of the density profile is explained in part by a Ware pinch [11]. The experimental pinch velocity is of the order of 0.1 m.s −1 and can be considered as a constant for r > 0.05 m, where r is the minor radius.…”