Application of ECH to the Study of Transport in ITER Baseline Scenario-like Discharges in DIII-D

¹ General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
² University of Texas at Austin, 1 University Station, Austin, Texas 78712, USA
³ Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
⁴ Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543-0451, USA
⁵ University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
⁶ University of California Los Angeles, P.O. Box 957099, Los Angeles, CA 90095, USA
⁷ Columbia University, New York, New York 10027, USA

^a Corresponding author: pinsker@fusion.gat.com

Published online: 12 March 2015

Abstract

Recent DIII-D experiments in the ITER Baseline Scenario (IBS) have shown strong increases in fluctuations and correlated reduction of confinement associated with entering the electron-heating-dominated regime with strong electron cyclotron heating (ECH). The addition of 3.2 MW of 110 GHz EC power deposited at ρ∼0.42 to IBS discharges with ∼3 MW of neutral beam injection causes large increases in low-k and medium-k turbulent density fluctuations observed with Doppler backscatter (DBS), beam emission spectroscopy (BES) and phase-contrast imaging (PCI) diagnostics, correlated with decreases in the energy, particle, and momentum confinement times. Power balance calculations show the electron heat diffusivity χ_e increases significantly in the mid-radius region 0.4<ρ<0.8, which is roughly the same region where the DBS and BES diagnostics show the increases in turbulent density fluctuations. Confinement of angular momentum is also reduced during ECH. Studies with the TGYRO transport solver show that the model of turbulent transport embodied in the TGLF code quantitatively reproduces the measured transport in both the neutral beam (NB)-only and in the NB plus EC cases. A simple model of the decrease in toroidal rotation with EC power is set forth, which exhibits a bifurcation in the rotational state of the discharge.