Impact of central ECCD on steady-state hybrid scenario in DIII-D
C. C. Petty, R. Nazikian, M. A. Van Zeeland, D. C. Pace, B. A. Grierson, Xi Chen, Egemen Kolemen, G. R. McKee, Ronald Prater, Francesca Turco · AIP conference proceedings · 2015
Steady-state" hybrid plasmas in DIII-D with zero surface loop voltage have been maintained for up to two current relaxation times using 3.4 MW of central electron cyclotron current drive (ECCD).In addition to driving ≈0.2 MA of plasma current, central ECCD leads to significant changes in Alfvén eigenmode (AE) activity and thermal transport.For neutral-beam-only heating, strong AE activity is observed that causes a ~35% degradation in the neutron rate.With central ECCD this AE activity is suppressed, replaced by a bursty energetic particle mode that appears more benign as the neutron rate is closer to the classical value.The electron thermal diffusivity increases by ≈50% for 2.4 MW of ECCD compared to neutral-beam-only cases.Fortunately, the global thermal confinement factor remains the same (H 98y2 =1.4) as the higher thermal transport for P EC =2.4 MW hybrids is offset by the decreased fast ion transport resulting from AE suppression.