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

R.I Pinsker,J.C Hosea,G.R Mckee,C.C Petty,T.C Luce,J.C Rost,L Schmitz,W.M Solomon,A Marinoni,G Taylor,B.A Grierson,F Turco,R.J Perkins,A.M Garofalo,M.E Austin,M Porkolab,D.R Ernst

doi:10.1051/epjconf/20158702003

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 � ~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 diffusivitye increases significantly in the mid-radius region 0.4<� <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.

Highlights

Properties of discharges in the baseline operating scenario for ITER [ITER-similar shape, N~2, q95~3, ELMing H-mode with H98(y,2)~1] are the subject of ongoing experiments on DIII-D; recent work has extended the similarities to include ITER-relevant torque and Te/Ti~1
Using the TGYRO nonlinear transport solver we evaluate the turbulent transport model embodied in the Trapped Gyro-Landau Fluid (TGLF) code, and find that the measured profiles appear to be consistent with the predicted ones inside
We have studied in detail the properties of a pair of DIII-D discharges in the ITER Baseline Scenario (IBS) regime, both of which were heated with NB throughout

Summary

The ITER Baseline Scenario on DIII-D

Properties of discharges in the baseline operating scenario for ITER [ITER-similar shape, N~2, q95~3, ELMing H-mode with H98(y,2)~1] are the subject of ongoing experiments on DIII-D; recent work has extended the similarities to include ITER-relevant (low) torque and Te/Ti~1 (dominant electron heating). The aim of this work is to study confinement in the low rotation, dominant electron heating regime (as from alphas in a burning D-T plasma in ITER). We compare ITER Baseline Scenario (IBS) discharges with neutral beam (NB) heating alone with otherwise identical discharges in which some of the NB power is replaced with electron cyclotron heating (ECH) EPJ Web of Conferences bifurcation into high and low rotation states of the discharge. We study the measured long- and intermediate-wavelength density fluctuations measured with the available diagnostics in both cases and find that the changes in the fluctuations appear to be qualitatively consistent with expectations derived from the modeling

Global confinement properties of IBS discharges with and without ECH

Simple bifurcation model for toroidal rotation slow-down with ECH

Effects on observed density fluctuations

Findings

Summary and conclusions