A study of maximum beta in experiments with a current ramp-down in the TUMAN-3M tokamak

The possibility is studied for achieving high values of the parameters beta (T) = 2 mu(0) [P]/B-T(2) and beta(N) = beta(T)(%)aB(T)/Ip, where I-p is the plasma current (in MA), B-T is the toroidal magnetic field (in T), and a i s the minor plasma radius (in m) characterizing the confinement efficiency of the tokamak magnetic field. The possibility is demonstrated for achievin g high values beta(T) = 2% and beta(N) = 2 in the Ohmic H-mode in a plasma column with a circular cross section in a boronized chamber. In order to fu rther increase beta(N), the current was ramped down in the quasisteady stag e of the Ohmic H-mode. After the current ramp-down, the plasma confinement was found to worsen due to switching off of the H-mode. Presumably, the rea son is that the heating power falls off below the threshold value.