MARFE phenomena in the HT-7 tokamak

Abstract

Multifaceted asymmetric radiation from the edge (MARFE) phenomena on the HT-7 superconducting tokamak are summarized in this paper. The best correlation has been found between the total input ohmic power and the product of the edge line average density and Z eff. The occurrence of MARFEs are strongly correlated with impurity density, and always occur at Z eff=3–8 ohmic discharges. In the HT-7 tokamak high Z eff discharges, it is found that the MARFEs usually occur at values of Z eff 1/2 ρ in the range of 0.5–0.7, where ρ=π a 2 n e/ I p (10 20 MA −1 m −1). In the case of good wall condition ( Z eff=1–2), the onset of MARFEs have not been observed before reaching the Greenwald density limit on the HT-7. Improved confinement mode induced by a MARFE is observed, and it is maintained for about 40 ms. MARFE cools the plasma edge, and the electron density profile is observed to become more narrow and peaked.