Abstract
High poloidal beta (ɛβp ~ 1) operation in steady state condition in tokamaks is of great interest and has previously been demonstrated using NBI, LHCD and low current (Ip ) plasma for a short time ( in tokamak plasma. In this work we report the first result of high βp 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 βp 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.
Highlights
Spherical Tokamak is an attractive choice for future fusion reactors for its ability to operate at high poloidal beta (ߚ = 2ߤ0〈〉/〈〉 ܤ2) value
We present a scenario of production of high βp plasma (Hβp > 1.3) by confining the energetic electrons produced by Electron Cyclotron Waves (ECWs) more flexibly in various operational regime with ECRH/ECCD
High βp plasma is produced in Ohmic plasma by offaxis fundamental and second harmonic ECCD at two different frequencies separately
Summary
The maximum achievable βp is limited by a so called equilibrium limit, where an Inboard Poloidal field Null (IPN) appears at the high field side of the vacuum vessel. In TFTR [8], a null point appeared at the inboard side in high βp plasma formed by ramping down the plasma current (Ip) in a NBI heated plasma. Such high βp plasma production and sustainment required > 16 MW of NBI power. We present a scenario of production of high βp plasma (Hβp > 1.3) by confining the energetic electrons produced by Electron Cyclotron Waves (ECWs) more flexibly in various operational regime with ECRH/ECCD.
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