Initial TRANSP simulations of lower hybrid heating and current drive in EAST

The EAST tokamak relies on Lower Hybrid (LH) heating and current drive for long pulse steady-state operation [1]. The combination of the two antennas—operating at 2.45 and 4.6 GHz—offers a unique opportunity to understand the synergy between LH waves and how to best exploit it for optimization of plasma performance towards demonstration of sustained steady-state. Because the DC electric field affects the fast electron distribution function, it is important that the magnetic equilibrium and the LH current drive are evolved self-consistently [2]. For this reason, time-dependent modeling is a necessary tool to guide experiments on EAST dedicated to access and sustainment of steady-state.The time-dependent evolution of an EAST plasma discharge with lower hybrid power has been modelled using the TRANSP code in combination with GENRAY and CQL3D. Analytical profiles for electron temperature and density were fitted to the measured profiles to remove noise from experimental measurements, as well as for ease of scaling studies. This enables quick scans of density to identify an optimal range for high LH current drive and maximum plasma performance. Preliminary results from scaling studies suggest there is a density threshold, beyond which current drive is significantly reduced. Additionally, there is some indication that the electron heating and the driven current do not scale similarly with density and temperature, indicating a complex nonlinearity in the absorption process. Future work will address the current challenges in time-dependent LH simulations and explore the synergy between the two LH antennas during simultaneous power injection.