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Title: Role of molecular effects in divertor plasma recombination

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Journal Article: Published Article
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Nuclear Materials and Energy
Additional Journal Information:
Journal Volume: 12; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-23 13:46:24; Journal ID: ISSN 2352-1791
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Citation Formats

Kukushkin, A. S., Krasheninnikov, S. I., Pshenov, A. A., and Reiter, D. Role of molecular effects in divertor plasma recombination. Netherlands: N. p., 2017. Web. doi:10.1016/j.nme.2016.12.030.
Kukushkin, A. S., Krasheninnikov, S. I., Pshenov, A. A., & Reiter, D. Role of molecular effects in divertor plasma recombination. Netherlands. doi:10.1016/j.nme.2016.12.030.
Kukushkin, A. S., Krasheninnikov, S. I., Pshenov, A. A., and Reiter, D. 2017. "Role of molecular effects in divertor plasma recombination". Netherlands. doi:10.1016/j.nme.2016.12.030.
title = {Role of molecular effects in divertor plasma recombination},
author = {Kukushkin, A. S. and Krasheninnikov, S. I. and Pshenov, A. A. and Reiter, D.},
abstractNote = {},
doi = {10.1016/j.nme.2016.12.030},
journal = {Nuclear Materials and Energy},
number = C,
volume = 12,
place = {Netherlands},
year = 2017,
month = 8

Journal Article:
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Publisher's Version of Record at 10.1016/j.nme.2016.12.030

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  • Analysis of the experimental data from tokamaks and linear divertor simulators leads to the conclusion that plasma recombination is a crucial element of plasma detachment. Different mechanisms of plasma recombination relevant to the experimental conditions of the tokamak scrape-off layer (SOL) and divertor simulators are considered. The physics of Molecular Activated Recombination (MAR) involving vibrationally excited molecular hydrogen are discussed. Although conventional Electron{endash}Ion Recombination (EIR) alone can strongly alter the plasma parameters, MAR impact can be substantial for both tokamak SOL plasma and divertor simulators. Investigation of the effects of EIR on the plasma flow in divertor simulators shows thatmore » due to the balances of (a) energy transport and electron cooling, and (b) the plasma flow and recombination, that EIR extinguishes the simulator plasma at an electron temperature about 0.15 eV. {copyright} {ital 1997 American Institute of Physics.}« less
  • We investigate the effects of hydrogen molecules and plasma recombination on plasma-neutral gas interactions in the recycling region of a tokamak divertor. We treat plasma-neutral interaction in a fluid approximation retaining the effects of plasma recombination and employing a neutral viscosity term to describe neutral interaction with the divertor plate. We consider both conventional three body recombination and recombination induced by the molecules through the formation of negative ions, H{sup -}, and molecular ions, such as H{sub 2}+, in combination with the ensuing neutralization, H{sup -} + H{sup +} {r_arrow} 2H and H{sub 2}+ + e {r_arrow} 2H. We showmore » that even in current tokamaks, the plasma recombination processes could be the dominant mechanism responsible for the decrease of plasma flux onto the target in detached regimes. Implementation of the recombination induced by the molecular effects significantly expand to much higher temperatures the range in which plasma recombination must be retained.« less
  • Cited by 1
  • Recent experiments in DIII-D helium plasmas are examined to resolve the role of atomic and molecular physics in major discrepancies between experiment and modeling of dissipative divertor operation. Helium operation removes the complicated molecular processes of deuterium plasmas that are a prime candidate for the inability of standard fluid models to reproduce dissipative divertor operation, primarily the consistent under-prediction of radiated power. Modeling of these experiments shows that the full divertor radiation can be accounted for, but only if measures are taken to ensure that the model reproduces the measured divertor density. Relying on upstream measurements instead results in amore » lower divertor density and radiation than is measured, indicating a need for improved modeling of the connection between the diverter and the upstream scrape-off layer. Furthermore, these results show that fluid models are able to quantitatively describe the divertor-region plasma, including radiative losses, and indicate that efforts to improve the fidelity of the molecular deuterium models are likely to help resolve the discrepancy in radiation for deuterium plasmas.« less
    Cited by 1
  • How predictions of deuterium atomic reaction rates in tokamak divertors are altered by changes in cross section data which are comparable with the uncertainty in published data is investigated. An extended neutral diffusion theory calculation, which includes D atoms and ground and excited state D{sub 2} molecules, is performed on a fixed background plasma. For the atoms, the principal relevant mechanisms are elastic scattering, charge exchange, ionization, and recombination. It is evaluated that the charge exchange and electron processes are known to an accuracy better than +/{minus}25{percent}, and it is concluded that this level of accuracy is sufficient for themore » present state of divertor calculations. Of significant concern is the fact that classical elastic cross sections which are widely used in divertor calculations differ substantially from a more accurate set of cross sections based on quantum mechanics, and that the latter produce predictions of neutral density and ionization rate which differ by orders of magnitude from predictions based on the classical cross sections. Opacity of the plasma to Lyman alpha radiation influences transport for high density plasma situations. The explicit representation of incident particles recycling as molecules is shown to significantly affect the neutral atom density and reaction rates near the divertor plate. In particular, the dissociation of even a small fraction of excited molecules significantly reduces the plasma ion population and increases the neutral atom population just in front of the plate in nearly detached plasmas. {copyright} {ital 1997 American Institute of Physics.}« less