Effect of the q(r) profile on electron transport barrier formation in the T-10 tokamak

The effect of the q(r) profile on transport barrier formation has been investigated in the T-10 tokamak using rapid current ramp-up with electron cyclotron resonance heating (ECRH). The enhanced core confinement (formation of the internal transport barrier (ITB)) arises earlier than the additional current penetrates in the core region. It is suggested that this process takes place due to decrease of magnetic surface density in the region of the rational q = 2 surface due to βp decrease, which is equivalent to dq/dr decrease near q = 2 surface. At various q-profiles, internal and external barriers were observed. Transient confinement improvement inside the ITB after the ECRH switch-off was also observed.