Improved edge charge exchange recombination spectroscopy in DIII-D

Chrystal, C.; Burrell, K.H.; Grierson, B. A.; Haskey, S. R.; Groebner, R. J.; Kaplan, David H.; Briesemeister, A.

doi:10.1063/1.4958915

Cited by 64 publications

(46 citation statements)

References 15 publications

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“…The divertor electron density, , , and temperature, , , are measured by Langmuir probes and the Divertor Thomson Scattering (DTS) systems, as shown in Figure 5. The pedestal electron density , and electron temperature, , , are diagnosed by the edge Thomson scattering array [31] and the pedestal C 6+ impurity density is measured by the edge CER system [23].…”

Section: Experimental Apparatus and Proceduresmentioning

confidence: 99%

Impact of ELM control techniques on tungsten sputtering in the DIII-D divertor and extrapolations to ITER

et al. 2019

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The free-streaming plus recycling model (FSRM) has recently been developed to understand and predict tungsten gross erosion rates from the divertor during edge localized modes (ELMs). In this work, the FSRM was tested against experimental measurements of W sputtering during ELMs, conducted via fast WI spectroscopy. Good agreement is observed using a variety of controlling techniques, including gas puffing, neutral beam heating, and plasma shaping to modify the pedestal stability boundary and thus the ELM behavior. ELM mitigation by pellet pacing was observed to strongly reduce W sputtering by flushing C impurities from the pedestal and reducing the divertor target electron temperature. No reduction of W sputtering was observed during the application of resonant magnetic perturbations (RMPs), in contrast to the prediction of the FSRM. Potential sources of this discrepancy are discussed. Finally, the framework of the FSRM is utilized to predict intra-ELM W sputtering rates in ITER. It is concluded that W erosion during ELMs in ITER will be caused mainly by free-streaming fuel ions, but free-streaming seeded impurities (N or Ne) may increase the erosion rate significantly if present in the pedestal at even the 1% level. Impurity recycling is not expected to cause significant W erosion in ITER due to the very low target electron temperature.

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Section: Experimental Apparatus and Proceduresmentioning

confidence: 99%

Impact of ELM control techniques on tungsten sputtering in the DIII-D divertor and extrapolations to ITER

et al. 2019

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“…This investigation is predicated on the accurate simultaneous measurement of many different plasma parameters, including electron and ion densities and temperatures and the equilibrium magnetic structure. The Doppler-shift ω dop and electron diamagnetic frequency ω * e are calculated from Carbon impurity measurements from charge-exchange recombination 29 and electron profile measurements from Thomson scattering 28 , respectively. Localized density fluctuations measurements are made with beam emissions spectroscopy in order to localize the instabilities in the plasma edge 41 .…”

Section: Methodsmentioning

confidence: 99%

“…In plasma experiments, magnetic fluctuations measured in the lab frame will have an additional frequency component given by the Doppler shift ω dop (ψ n ). By exploiting high spatial and temporal resolution diagnostics on the DIII-D tokamak 28,29 , we can track the structure of both ω e * and ω dop through time, enabling an investigation of the dynamical evolution of plasma microinstabilities in tokamaks.…”

Section: Time-dependent Mtm Identificationmentioning

confidence: 99%

Perturbative Determination of Plasma Microinstabilities in Tokamaks

Nelson,

Laggner,

Diallo

et al. 2021

Preprint

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Recently, theoretical analysis has identified plasma microinstabilities as the primary mechanism responsible for anomalous heat transport in tokamaks. In particular, the microtearing mode (MTM) has been credited with the production of intense electron heat fluxes, most notably through a thin self-organized boundary layer called the pedestal. Here we exploit a novel, time-dependent analysis to compile explicit experimental evidence that MTMs are active in the pedestal region. The expected frequency of pedestal MTMs, calculated as a function of time from plasma profile measurements, is shown in a dedicated experiment to be in excellent agreement with observed magnetic turbulence fluctuations. Further, fast perturbations of the plasma equilibrium are introduced to decouple the instability drive and resonant location, providing a compelling validation of the analytical model. This analysis offers strong evidence of edge MTMs, validating the existing theoretical work and highlighting the important role of MTMs in regulating electron heat flow in tokamaks.

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“…The diagnostics in this discharge were aligned to provide high resolution measurements in the vicinity of the q = 2 surface. In addition, the discharges use fast (1 ms) CER measurements [31] to provide time resolved measurements of the toroidal and poloidal flows. These high resolution measurement enable high fidelity kinetic reconstructions which are needed for simulation.…”

Section: A Experimental Equilibriummentioning

confidence: 99%

Growing Neoclassical Tearing Modes Seeded via Transient-Induced-Multimode Interactions

Howell,

King,

Callen

et al. 2021

Preprint

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Nonlinear extended MHD simulations demonstrating seeding of neoclassical tearing modes (NTMs) via MHD-transient-induced multimode interactions are presented. Simulations of NTMs are enabled by two recent NIMROD code developments: the implementation of heuristic neoclassical stresses and the application of transient magnetic perturbations (MPs) at the boundary. NTMs are driven unstable by the inherently pressure driven kinetic bootstrap current, which arises due to collisional viscosity between passing and trapped electrons. These simulations use heuristic closures that model the neoclassical electron and ion stresses. NTM growth requires a seed island, which is generated by a transiently applied MP in simulations. The capability is demonstrated using kineticbased reconstructions with flow of a DIII-D ITER Baseline Scenario discharge [R.J. La Haye, et al., Proceedings IAEA FEC 2020]. The applied MP seeds a 2/1 NTM that grows in two phases: a slow growth phase followed by a faster robust growth phase like that observed experimentally. Additionally, an evolving sequence of higher order core modes are excited at first. Power transfer analysis shows that nonlinear interactions between the core modes and the 2/1 helps drive the initial slow growth. Once the induced 2/1 magnetic island reaches a critical width, the NTM transitions to faster robust growth which is well described by the nonlinear modified Rutherford equation. This work highlights the role of nonlinear mode coupling in seeding NTMs.

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Improved edge charge exchange recombination spectroscopy in DIII-D

Cited by 64 publications

References 15 publications

Impact of ELM control techniques on tungsten sputtering in the DIII-D divertor and extrapolations to ITER

Impact of ELM control techniques on tungsten sputtering in the DIII-D divertor and extrapolations to ITER

Perturbative Determination of Plasma Microinstabilities in Tokamaks

Growing Neoclassical Tearing Modes Seeded via Transient-Induced-Multimode Interactions

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