Observation of Improved Confinement in the Initial Phase of the Ohmic Discharge in the TUMAN-3M.

Introduction Confinement improvement in the plasma core was observed in many experiments with auxiliary heating [1]. In some experiments with essential electron heating or current drive the confinement improvement in the core was observed in electron component. In those experiments a positive role of negative or low magnetic shear s=(r/q)⋅(∂q/∂r) was established to be favourable for the internal transport barrier formation [2]. In purely ohmically heated plasma the formation of electron transport barrier is difficult because of the tie between the safety factor profile q(r) and the heat source radial distribution. In recent experiments in the TUMAN-3M tokamak a temporal confinement enhancement in electron component was observed in the initial phase of the discharge in the ohmically heated plasma. The paper describes experimental results demonstrating the confinement improvement. The role of q(r) evolution in the observed phenomenon is discussed.