ANOMALOUS CURRENT DIFFUSION AND IMPROVED CONFINEMENT IN THE HT-6M TOKAMAK

Current diffusion was studied during edge ohmic heating (EOH) experime nts in the HT-6M tokamak. The EOH power system makes the plasma curren t linearly ramp up from an initial steady state (I(p)=55 kA) to a seco nd steady state (I(p)=60 kA) at a fast ramp rate of 12 MA/s. A stable discharge of an improved confinement was observed experimentally in th e HT-6M tokamak after the plasma current was ramped to rise rapidly to a second steady state. The plasma current is ramped up much faster th an both the classical skin time and neoclassical skin time. Fast curre nt ramp up increases the anomalous current diffusion. The measured val ues of beta(P) + l(i)/2 and the soft X-ray sawtooth inversion radius i mply the anomalous current penetration. The mechanism of anomalous pen etration and improved confinement is discussed.