Temporal measurement of electron density, metastable-atom density, and reduced electric field are used to infer the dynamic behavior of the excitation rates describing electron-atom collision-induced excitation in the positive column of a 1 Torr argon plasma by invoking plausible assumptions regarding the shape of the electron energy distribution function performed in Adams et al (2012 Phys. Plasmas 19 023510). These inferred rates are used to predict the 420.1 nm to 419.8 nm argon emission ratio, which agree with experimental results when the assumptions are applicable. Thus the observed emission ratio is demonstrated to be dependent on the metastable-atom density, electron density, and reduced electric field. The established confidence in the validity of this emission-line-ratio model allows us to predict metastable argon-atom density during the post-transient phase of the pulse as suggested by De Joseph et al (2005 Phys. Rev. E 72 036410). Similar inferences of electron density and reduced electric field based on readily available diagnostic signatures may also be afforded by this model. Keywords: optical emission spectroscopy (OES), 420.1-419.8 nm emission-line ratio, 1s 5 metastable argon atom, reduced electric field (E/N), electron energy distribution, time-resolved, extended corona model

View the article online for updates and enhancements. Related content Correlating metastable-atom density, reduced electric field, and electron energy distribution in the post-transient stage of a 1-Torr argon discharge J B Franek, S H Nogami, V I Demidov et al.-Reply to comment on 'Correlating metastable-atom density, reduced electric field, and electron energy distribution in the post-transient stage of a 1 Torr argon discharge' 2015 Plasma Sources Sci. Technol. 24 034009 J B Franek, S H Nogami, V I Demidov et al.-Comment on 'Correlating metastable-atom density, reduced electric field, and electron energy distribution in the post-transient stage of a 1 Torr argon discharge' (2015 Plasma Source Sci. Technol. 24 034009

Results from a joint experimental and computational effort studying the effect of resonant magnetic perturbations (RMPs) on microturbulence levels and their connection to zonal flows in the DIII-D tokamak L-mode are presented. Beam emission spectroscopy measurements show a direct increase in density fluctuations at microturbulent scales with increasing RMP amplitude, suggesting that magnetic activity introduced by the RMP affects the regulation of microturbulence on DIII-D. This is analogous to how MHD-scale magnetic fluctuations arising from tearing modes have been observed in simulations to increase microturbulence levels in the reversed-field pinch (RFP). In the RFP, this is attributed to magnetic fluctuations eroding turbulence-limiting zonal flows; this work examines if a similar mechanism is present for DIII-D microturbulence. Gyrokinetic simulations find that the application of an RMP corresponds directly to a decrease in zonal flow levels, producing a similar increase of turbulent fluctuation levels over a range of RMP amplitudes as observed in the experiment.

DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.

The attention to a detailed analysis by Sadeghi [1] of our paper [2], using Weatherford and Barnat [3] for reference information is appreciated and motivates us to clarify points in our paper referred to in the Comment [1]. In this Reply, we respond to the two remarks by Sadeghi [1] claiming to render as unjustified our original conclusion based on validity of the 420.1/419.8 nm emission intensity ratio method for the estimate of argon metastable density, and clear up other possible misinterpretations of the data presented in our paper [2].