Role of ponderomotive density expulsion in ion Bernstein wave coupling to the core plasma

Russell, D. A.; Myra, J. R.; D’Ippolito, D. A.

doi:10.1063/1.872772

Cited by 9 publications

(13 citation statements)

References 30 publications

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“…Non-linear interactions of the RF power with the plasma edge, such as RF sheaths and parametric instabilities, can produce poor IBW penetration in the bulk and impurity influxes. This is what inhibited the reproducibility of successful IBW results obtained in previous experiments [24,25,26]. Non-linear edge phenomena occur as a consequence of the onset of a strong turbulence regime.…”

Section: Introductionmentioning

confidence: 90%

Analysis of the heating scenarios of the ion Bernstein wave (IBW) experiment in Frascati Tokamak Upgrade

et al. 2002

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Ion Bernstein waves (IBWs) have been proposed as useful for heating and improving transport in tokamak plasmas. The experiments carried out so far have not provided a sufficient assessment of this concept, due to the occurrence of parasitic phenomena that caused poor reproducibility of IBW heating and confinement effects. An experiment on FTU has given the first test of IBW coupling to a tokamak plasma by a waveguide antenna utilized in place of the standard dipole antenna. In addition, the experiment operates at a high frequency that is expected to reduce the non-linear wave-plasma interaction at the edge. These phenomena were considered to be the cause of the lack of RF power penetration in the plasma bulk and of the production of impurity influx. The possible IBW experimental scenarios expected for the FTU plasma are described. To perform this analysis, quasi-linear and non-linear models are utilized for the wave propagation, damping and turbulence suppression suitable for transport barrier formation. As a result of this study, FTU is expected to be a useful facility for testing the IBW concept for advanced tokamaks.

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Section: Introductionmentioning

confidence: 90%

Analysis of the heating scenarios of the ion Bernstein wave (IBW) experiment in Frascati Tokamak Upgrade

et al. 2002

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“…The code, which is limited to the k y = 0 case, has been described in detail elsewhere. 7 In this code, the CM geometry is a bit different than in Sec. IV because a vacuum region rather than a low density halo plasma is assumed beyond the Faraday screen.…”

Section: Diffuse Profile Calculations With Self-consistent Ponderomentioning

confidence: 99%

“…This feature and the role of ponderomotive steepening and induced reflection have been treated elsewhere. 7 The TFTR experimental observation that loading depends on poloidal (y) phasing (0-0-0-0 or 0-0-π-π) is suggestive of the notion that the CM propagates only at low k y . In this paper, we explore this dependence and the dependence of the power split P out /P rf on dissipation in the halo plasma, where P out = P rf − P halo .…”

Section: Introductionmentioning

confidence: 99%

Coaxial mode excitation and dissipation in ion Bernstein wave experiments

et al. 2000

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In recent ion Bernstein wave (IBW) heating experiments on the Tokamak Fusion Test Reactor (TFTR) [J. R. Wilson. R. E. Bell, S. Bernabei, K. Hill et al., Phys. Plasmas 5, 1721 (1998)] a velocity shear layer in the plasma core was obtained. The magnitude of velocity shear was believed to be too small to create an internal transport barrier, because of parasitic edge processes which reduced the power coupled to the core. In this paper we investigate these rf (radio frequency) edge processes by employing a model which includes both coaxial modes and their dissipation in rf plasma sheaths. The coaxial mode (here, an electron plasma wave trapped in the halo plasma between the lower hybrid layer and the vessel wall) can propagate at low poloidal wave numbers. This feature is shown to relate to the observed poloidal phasing dependence of the antenna loading. Results of analytical models and a three-dimensional antenna code are presented. The experimentally observed loading is also nonlinear, being larger at very low powers. This feature is explored using an rf sheath dissipation model. Loading into the coaxial mode is expected to maximize when the density gradient at the lower hybrid layer is steep, preventing efficient mode transformation to the IBW. The role of ponderomotive force in modifying the density profile is also discussed.

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“…This feature, was not expected from traditional direct launch IBW theory, but could be explained by a linear theory model 40 which assumed ponderomotive depletion of density in front of the antenna, and allowed the energy to be absorbed at the ensuing lower hybrid resonance (LHR). A related 1-D nonlinear model, 41 which explicitly included ponderomotive profile steepening, showed enhanced wave reflection near the LHR that effectively channeled energy into a coaxial mode propagating in the halo plasma. Furthermore, the phasing properties of this mode were consistent with loading and heating efficiency measurements on TFTR.…”

Section: Ibw Edge Interactionsmentioning

confidence: 99%

Nonlinear ICRF-plasma interactions

et al. 2006

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Abstract. The well developed linear theory of ICRF (including FW, HHFW and IBW) interactions with plasma has enjoyed considerable success in describing antenna coupling and wave propagation, and provides a well-known framework for calculating power absorption, current drive, etc. In some situations, less well studied nonlinear effects are of interest, such as flow drive, ponderomotive forces, rf sheaths, parametric decay and related interactions with the edge plasma. Standard ICRF codes have begun to integrate this physics to achieve improved modeling capabilities. This paper concentrates on basic rf-plasma-interaction physics with illustrative applications to tokamaks. For FW antennas, the parallel electric field near launching structures is known to drive rf-sheaths which can give rise to convective cells, interaction with plasma "blobs", impurity production, and edge power dissipation. In addition to sheaths, IBW waves in the edge plasma are subject to strong ponderomotive effects and parametric decay. In the core plasma, slow waves can sometimes induce nonlinear effects. Mechanisms by which these waves can influence the radial electric field and its shear are summarized, and related to the general (reactive-ponderomotive and dissipative) force on a plasma from rf waves. It is argued that there are significant opportunities now for new predictive capabilities by advances in integrated simulation.

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Role of ponderomotive density expulsion in ion Bernstein wave coupling to the core plasma

Cited by 9 publications

References 30 publications

Analysis of the heating scenarios of the ion Bernstein wave (IBW) experiment in Frascati Tokamak Upgrade

Analysis of the heating scenarios of the ion Bernstein wave (IBW) experiment in Frascati Tokamak Upgrade

Coaxial mode excitation and dissipation in ion Bernstein wave experiments

Nonlinear ICRF-plasma interactions

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