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Title: Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1287746
Grant/Contract Number:
SC0006103; SC0013911
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 10; Related Information: CHORUS Timestamp: 2016-08-10 03:08:01; Journal ID: ISSN 0029-5515
Publisher:
IOP Publishing
Country of Publication:
IAEA
Language:
English

Citation Formats

Schmitz, O., Ida, K., Kobayashi, M., Bader, A., Brezinsek, S., Evans, T. E., Funaba, H., Goto, M., Mitarai, O., Morisaki, T., Motojima, G., Nakamura, Y., Narushima, Y., Nicolai, D., Samm, U., Tanaka, H., Yamada, H., Yoshinuma, M., Xu, Y., and the TEXTOR and LHD Experiment Groups. Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR. IAEA: N. p., 2016. Web. doi:10.1088/0029-5515/56/10/106011.
Schmitz, O., Ida, K., Kobayashi, M., Bader, A., Brezinsek, S., Evans, T. E., Funaba, H., Goto, M., Mitarai, O., Morisaki, T., Motojima, G., Nakamura, Y., Narushima, Y., Nicolai, D., Samm, U., Tanaka, H., Yamada, H., Yoshinuma, M., Xu, Y., & the TEXTOR and LHD Experiment Groups. Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR. IAEA. doi:10.1088/0029-5515/56/10/106011.
Schmitz, O., Ida, K., Kobayashi, M., Bader, A., Brezinsek, S., Evans, T. E., Funaba, H., Goto, M., Mitarai, O., Morisaki, T., Motojima, G., Nakamura, Y., Narushima, Y., Nicolai, D., Samm, U., Tanaka, H., Yamada, H., Yoshinuma, M., Xu, Y., and the TEXTOR and LHD Experiment Groups. Tue . "Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR". IAEA. doi:10.1088/0029-5515/56/10/106011.
@article{osti_1287746,
title = {Enhancement of helium exhaust by resonant magnetic perturbation fields at LHD and TEXTOR},
author = {Schmitz, O. and Ida, K. and Kobayashi, M. and Bader, A. and Brezinsek, S. and Evans, T. E. and Funaba, H. and Goto, M. and Mitarai, O. and Morisaki, T. and Motojima, G. and Nakamura, Y. and Narushima, Y. and Nicolai, D. and Samm, U. and Tanaka, H. and Yamada, H. and Yoshinuma, M. and Xu, Y. and the TEXTOR and LHD Experiment Groups},
abstractNote = {},
doi = {10.1088/0029-5515/56/10/106011},
journal = {Nuclear Fusion},
number = 10,
volume = 56,
place = {IAEA},
year = {Tue Aug 09 00:00:00 EDT 2016},
month = {Tue Aug 09 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1088/0029-5515/56/10/106011

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  • In this paper, results of a direct comparison of TEXTOR and DIII-D experiments with resonant magnetic perturbation (RMP) fields are presented. This comparison of resistive L-mode plasmas at TEXTOR with highly conductive H-mode plasmas at DIII-D is useful to identify generic physics mechanisms during application of RMP fields with a strong field line pitch angle alignment in the plasma edge. A reduction in the pedestal electron pressure p(e) with increasing extension of the vacuum modelled stochastic layer and p(e) recovery with decreasing layer width is found caused by a q(95) resonant reduction in the edge (0.8 < Psi(N) < 0.95)more » electron temperature T-e(q(95)) on both devices. For RMP edge-localized mode (ELM) suppressed H-mode plasmas at DIII-D, the gradients del T-e and nominal values of T-e are reduced in this edge region while increasing in the pedestal (0.95 < Psi(N) < 1.0) with RMP field applied and both are highly dependent on q(95). In contrast, an increase in the central ion temperature with strong steepening of the ion temperature profile at mid-radius is found-again being highly dependent on q(95). However, these resonant thermal transport effects are only seen in high triangularity plasmas revealing a strong shape dependence of the thermal transport. In contrast to the highly q(95) dependent thermal transport features, the reduction of n(e)-known as density pump out-shows a much weaker dependence on q(95). We show the potential to reduce the RMP induced particle pump out by fine tuning of the RMP spectral properties. At low resonant field amplitudes enhanced particle confinement is seen in high-field side limited L-mode discharges on both devices while higher resonant field amplitudes yield particle pumps out.« less
  • The electrostatic response of the edge plasma to a magnetic island induced by resonant magnetic perturbations to the plasma edge of the circular limiter tokamak TEXTOR is analyzed. Measurements of plasma potential are interpreted by simulations with the Hamiltonian guiding center code ORBIT. We find a strong correlation between the magnetic field topology and the poloidal modulation of the measured plasma potential. The ion and electron drifts yield a predominantly electron driven radial diffusion when approaching the island X-point while ion diffusivities are generally an order of magnitude smaller. This causes a strong radial electric field structure pointing outward frommore » the island O-point. The good agreement found between measured and modeled plasma potential connected to the enhanced radial particle diffusivities supports that a magnetic island in the edge of a tokamak plasma can act as convective cell. We show in detail that the particular, non-ambipolar drifts of electrons and ions in a 3D magnetic topology account for these effects. An analytical model for the plasma potential is implemented in the code ORBIT, and analyses of ion and electron radial diffusion show that both ion- and electron-dominated transport regimes can exist, which are known as ion and electron root solutions in stellarators. This finding and comparison with reversed field pinch studies and stellarator literature suggest that the role of magnetic islands as convective cells and hence as major radial particle transport drivers could be a generic mechanism in 3D plasma boundary layers.« less
  • The first encouraging experiments demonstrating direct, explicit control of the He{sup 2+} density in a tokamak plasma have been performed in the TEXTOR tokamak with the Advanced Limiter Test-II pump limiter. Helium is injected in a short gas puff from the outside of the plasma, is observed to reach the plasma core, and then is readily removed from the plasma. An exhaust efficiency of {approximately}8% is obtained. Active charge-exchange spectroscopy is used to study the exhaust and transport of He{sup 2+} within the plasma, and the density evolution is modeled with a diffusive-convective transport code.