Analysis of bifurcation phenomena in the electron internal transport barrier in the large helical device

The electron internal transport barrier (eITB) 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 x B shear has been introduced by means of the factor [1 + (tauomega(ExB))(gamma)](-1). Simulation results show a clear critical transition between plasma regimes with rather flat electron temperature profiles (non-) to a steeped one (with eITB) when average density is low enough. With the aim of studying the eITB formation as a phase transition phenomenon, the electron average density is taken as the control parameter and the E x B shearing rate as the order parameter. Results show how the eITB formation in LHD is compatible with a continuum phase transition with critical exponent beta = 0.40.