Role of collisionless trapped electron mode in tokamak plasmas with electron internal transport barrier

A self-sustained turbulence model for collisionless trapped electron mode is presented to examine the role of dynamics of trapped electrons in forming electron internal transport barrier (ITB) in tokamak plasmas with negative magnetic shear. Results show. that strong negative magnetic shear as well as large Shafranov shift can lead to the precession drift reversal of trapped electrons and large reduction, of anomalous electron heat conductivity; it may further trigger the formation of electron ITB. The complete precession drift reversal seems to be in good agreement with the onset condition of electron ITB observed in JT-60U discharges.