Thresholds of ion turbulence in tokamaks
The anomalous ion heat transport observed in tokamak discharges such as monster sawtooth, hot ion or ohmic regimes with T(e) greater than T(i) may be explained on the basis of ionic turbulence. The parameter controlling the onset of such turbulence is usually the thermal gradient length normalised to the major radius. Although the values of this are usually of the order of 0.3 for T(e) = T(i), values as low as 0.1 are found in discharges which do not exhibit the predicted large enhancement of the ion diffusivity. This threshold has been calculated using a linear kinetic code which involves all resonances for trapped and circulating particles in the exact toroidal equilibrium geometry. Two major results contradict models based on fluid theory. First, the most dangerous modes are trapped ion-driven modes. Secondly, the threshold is much smaller than the previous theoretical values. Ion turbulence is therefore more stable than usually admitted.
Bibliographic Reference: Paper presented: 18th European Conference of the EPS-Plasma Physics Division, Berlin (DE), June 3-7, 1991
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Record Number: 199110365 / Last updated on: 1994-12-02
Original language: en
Available languages: en