Core impurity transport in Alcator C-Mod L-, I- and H-mode plasmas

Rice, J. E.; Reinke, M.L.; Gao, C.; Howard, N. T.; Chilenski, Mark; Delgado‐Aparicio, L.; Granetz, R.; Greenwald, M.; Hubbard, A.; Hughes, J. W.; Irby, J.; Lin, Y.; Marmar, E.; Mumgaard, R.; Scott, S. D.; Terry, J. L.; Walk, J.; White, Anne; Whyte, D.G.; Wolfe, S.; Wukitch, S.

doi:10.1088/0029-5515/55/3/033014

Cited by 50 publications

(68 citation statements)

References 85 publications

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“…It is interesting to note that the measured impurity diffusivity in C-Mod L-mode plasmas decreases with plasma current as D eff ∝ I P −.7 [1]. Similar observations have been made on other devices [49,50,51].…”

Section: Discussionsupporting

confidence: 80%

“…It is not possible to explore this effect in Ohmic discharges without auxiliary heating power since the electron temperature is fixed at fixed density. The impurity confinement time τ I is independent of density for Ohmic plasmas [1]; similar observations are seen in Imode. In H-mode plasmas, where the up/down asymmetry disappears, there is a large neo-classical-like edge inward pinch (see Refs.…”

Section: Discussionsupporting

confidence: 75%

“…The edge brightness profiles in H-mode are very narrow compared to the L-and I-mode profiles since at these low electron temperatures, the upper 2p levels can only be populated by radiative recombination of fully stripped Ar 18+ , but because of the strong inward impurity pinch in H-mode (see Refs. in [1]), there is insufficient Ar 18+ (which must be born in the plasma core and diffused outwards quickly) at this radius. There is also a significant change to the background electron density profile in H-mode for this discharge, as demonstrated in Fig.…”

Section: Observed Scalings Of the Asymmetry Magnitude With Plasma Parmentioning

confidence: 98%

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Up/down impurity density asymmetries in C-Mod plasmas

Rice¹,

Reinke²,

Cao³

et al. 2018

Nucl. Fusion

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Brightness profiles of x-ray emission from H-like Ar 17+ exhibit a distinct up/down asymmetry under certain operating conditions in C-Mod plasmas, indicating that impurity densities are not constant on flux surfaces with r/a between ∼0.8 and ∼0.95. In Land I-mode plasmas, there is an x-ray brightness excess, up to a factor of 8, on the side opposite to the ion B×∇B drift direction. This effect is not observed in H-mode plasmas, presumably due to edge impurity transport being dominated by a strong inward pinch, which is absent in L-and I-mode. The magnitude of the asymmetry in L-and I-mode decreases with increasing plasma current, similar to the observed decrease in radial impurity diffusivity. In I-mode, where the codependence between electron density and temperature can be broken with ICRF heating power, the asymmetry magnitude is found to decrease with increasing density and with increasing edge temperature at fixed density. These measurements exhibit some qualitative features of neo-classical expectations but the observed asymmetry magnitude is much larger than predicted and some scalings with plasma parameters are not seen. The up/down asymmetry appears to be largest when the cross field impurity diffusivity is the highest.

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Section: Discussionsupporting

confidence: 80%

Section: Discussionsupporting

confidence: 75%

Section: Observed Scalings Of the Asymmetry Magnitude With Plasma Parmentioning

confidence: 98%

See 1 more Smart Citation

Up/down impurity density asymmetries in C-Mod plasmas

Rice¹,

Reinke²,

Cao³

et al. 2018

Nucl. Fusion

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“…We have performed experiments at C-Mod on impurity transport and particle transport in I-mode, for comparisons with L-mode and H-mode. 42 Future simulation work will explore the particle transport using these data sets. We plan to make direct comparisons between nonlinear GYRO simulation results and measured impurity particle transport using established techniques.…”

Section: Discussionmentioning

confidence: 99%

Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experimenta)

et al. 2015

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For the first time, nonlinear gyrokinetic simulations of I-mode plasmas are performed and compared with experiment. I-mode is a high confinement regime, featuring energy confinement similar to H-mode, but without enhanced particle and impurity particle confinement [D. G. Whyte et al., Nucl. Fusion 50, 105005 (2010)]. As a consequence of the separation between heat and particle transport, I-mode exhibits several favorable characteristics compared to H-mode. The nonlinear gyrokinetic code GYRO [J. Candy and R. E. Waltz, J Comput. Phys. 186, 545 (2003)] is used to explore the effects of E Â B shear and profile stiffness in I-mode and compare with L-mode. The nonlinear GYRO simulations show that I-mode core ion temperature and electron temperature profiles are more stiff than L-mode core plasmas. Scans of the input E Â B shear in GYRO simulations show that E Â B shearing of turbulence is a stronger effect in the core of I-mode than L-mode. The nonlinear simulations match the observed reductions in long wavelength density fluctuation levels across the L-I transition but underestimate the reduction of long wavelength electron temperature fluctuation levels. The comparisons between experiment and gyrokinetic simulations for I-mode suggest that increased E Â B shearing of turbulence combined with increased profile stiffness are responsible for the reductions in core turbulence observed in the experiment, and that I-mode resembles H-mode plasmas more than L-mode plasmas with regards to marginal stability and temperature profile stiffness. V C 2015 AIP Publishing LLC.

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“…The poor particle confinement in the I-mode also contributes to a low core impurity level and sustains the operation performance. [22,23] In this paper, the typical I-mode investigation in EAST is presented for the first time. In 2014, the upper divertor was upgraded to full tungsten, while the lower divertor was conserved to be carbon.…”

Section: Introductionmentioning

confidence: 99%

I-mode investigation on the Experimental Advanced Superconducting Tokamak

et al. 2019

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By analyzing large quantities of discharges in the unfavorable ion B ×∇B drift direction, the I-mode operation has been confirmed in EAST tokamak. During the L-mode to I-mode transition, the energy confinement has a prominent improvement by the formation of a high-temperature edge pedestal, while the particle confinement remains almost identical to that in the L-mode. Similar with the I-mode observation on other devices, the E r profiles obtained by the eight-channel Doppler backscattering system (DBS8)[1] show a deeper edge E r well in the I-mode than that in the L-mode. And a weak coherent mode (WCM) with the frequency range of 40-150 kHz is observed at the edge plasma with the radial extend of about 2-3 cm. WCM could be observed in both density fluctuation and radial electric field fluctuation, and the bicoherence analyses showed significant couplings between WCM and high frequency turbulence, implying that the E r fluctuation and the caused flow shear from WCM should play an important role during I-mode. In addition, a low-frequency oscillation with a frequency range of 5-10 kHz is always accompanied with WCM, where GAM intensity is decreased or disappeared. Many evidences show that the a low-frequency oscillation may be a arXiv:1902.04750v3 [physics.plasm-ph]

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Core impurity transport in Alcator C-Mod L-, I- and H-mode plasmas

Cited by 50 publications

References 85 publications

Up/down impurity density asymmetries in C-Mod plasmas

Up/down impurity density asymmetries in C-Mod plasmas

Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experimenta)

I-mode investigation on the Experimental Advanced Superconducting Tokamak

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