Boundary plasma behavior under different wall conditions on HT-7 tokamak

The boundary plasma behaviors under different wall conditions on the HT-7 tokamak were investigated using a reciprocating Langmuir probe system. The ion cyclotron radio frequency (ICRF) boronization has become a routine wall conditioning technique on HT-7. After ICRF boronization, the turbulence de-correlation and radial electric field shear in the plasma edge region accompanied the strong reduction of impurity radiation, which resulted in the enhancement of edge transport barrier. The central chord average density scanning experiment had been carried out on HT-7. Accompanying the increase of density an evident increase of radial electric field shear could be found in the plasma edge region, which could be responsible for the turbulence de-correlation and improved particle confinement. The results presented here suggest a link between wall conditions and boundary plasma physics; especially interplay between atomic processes and turbulence through the formation of radial electric field shear in the plasma edge region.