Density profile peaking in the presence of ECRH heating in TCV
Experimental observations in stationary ECRH discharges in TCV show that additional heating has a strong effect on the electron density profile. In the absence of MHD activity or strong internal transport barriers, additional electron heating generally leads to a broadening of the density profiles with respect to the Ohmic target plasma profiles. In the ECRH L-mode and in the presence of weak electron internal transport barriers, the density peaking factor depends on the edge safety factor, the power deposition profile and ECRH power. Beyond a critical power of some 0.5 MW, the power dependence saturates. The edge safety factor dependence is supportive of turbulent equipartition (TEP) theory, which predicts inward convection in the presence of turbulence. The observation of a reduction in the peaking with central electron heating supports drift wave turbulence theory, which predicts the decrease of inward particle convection in addition to the inward convection by TEP, when trapped electron modes are destabilized, thereby reducing the net inward convection.