The electron internal transport barrier ($e\mathrm{ITB}$) formation in the Large Helical Device (LHD) is studied with the transport code TOTAL and a GyroBohm-like model. The reduction of anomalous transport by the $E\times B$ shear has been introduced by means of the factor $[1+(\tau {\omega }_{E\times B}{)}^{\gamma }{]}^{-1}$. Simulation results show a clear critical transition between plasma regimes with rather flat electron temperature profiles (non-$e\mathrm{ITB}$) to a steeped one (with $e\mathrm{ITB}$) when average density is low enough. With the aim of studying the $e\mathrm{ITB}$ formation as a phase transition phenomenon, the electron average density is taken as the control parameter and the $E\times B$ shearing rate as the order parameter. Results show how the $e\mathrm{ITB}$ formation in LHD is compatible with a continuum phase transition with critical exponent $\beta =0.40$.

• Received 4 November 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.105007