Observation of a plateau electron distribution function due to electron cyclotron heating for an efficient plug potential formation

A plateau-shaped electron distribution function is observed when an electrostatic electron-trapping potential is formed by the electron cyclotron heating (ECH) in the plug region of the GAMMA 10 tandem mirror. Also, a remarkable thermal isolation effect due to a kV-range thermal barrier is observed along with the difference between distribution functions in thermally separated regions. These new findings as well as the relation between ion-confining potentials and thermal-barrier potentials in the kV range consistently support the validity of Cohen's strong ECH theory.