Highβ_pplasma formation using off-axis ECCD in Ohmic heated plasma in the spherical tokamak QUEST

Abstract

Abstract. High poloidal beta (Hβ p ~1) operation in steady state condition in tokamaks is of great interest and has previously been demonstrated using NBI, LHCD and low current (I p ) plasma for a short time (<0.5 s). A very few experiments however, have been performed towards the investigation of highest obtainable β p in tokamak plasma. In this work we report the first result of high β p production and its sustainment though an off axis ECCD at two different frequencies (fundamental and second harmonic) in Ohmic (OH) target plasma. With application of ECCD, plasma β p increased to encounter an equilibrium limit and the standard limiter configuration is transformed to an Inboard Poloidal field Null (IPN) configuration. Both off-axis and on-axis ECCD is studied and found to have some distinctive features, which are discussed in this paper.