Spectral effects on fast wave core heating and current drive

Phillips, C. K.; Bell, R.E.; Berry, Lee A.; Bonoli, P.T.; Harvey, R. W.; Hosea, J. C.; Jaeger, E. F.; LeBlanc, B.; Ryan, P.; Taylor, G. N.; Valeo, E. J.; Wilgen, John B; Wilson, James R.; Yuh, Howard

doi:10.1088/0029-5515/49/7/075015

Cited by 38 publications

(33 citation statements)

References 24 publications

(44 reference statements)

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“…The former is in agreement with the experimental observations found in NSTX [6,17,18,19,20] and DIII-D [2]. On the other hand, the latter is not easy to link directly to the experimental observations and additional studies might be required.…”

Section: Discussionsupporting

confidence: 89%

“…Figure 2 in [24], the amplitude of the electric field starts to increase in the SOL region as n ant increases beyond this cutoff value. This density is associated with the FW wave cut-off (the right-hand cutoff), which for a single ion species plasma and ω < |ω ce | (ω ce is the electron cyclotron angular frequency), can be written as [6,17,24]…”

Section: D Aorsa Rusults For Nstxmentioning

confidence: 99%

“…In the recent years, a large effort has been made to understand the main physical mechanisms behind the interaction between RF waves and the SOL, such as parametric decay [11,3,12,13], sheath effects [14,15], etc.. Recently, experimental studies employing high harmonic fast wave (HHFW) heating on the National Spherical Torus eXperiment (NSTX) [16], a low aspect ratio tokamak, have shown that substantial HHFW power loss (up to 60% of the HHFW power coupled from the antenna) can occur along the open field lines in the SOL [6,17,18,19,20]. This paper examines FW power loss in the SOL by using the numerical full wave simulation code AORSA [21], in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain [22].…”

Section: Introductionmentioning

confidence: 99%

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Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes^*

et al. 2015

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Abstract. Several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves, have found strong interaction between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 3D AORSA results for National Spherical Torus eXperiment (NSTX), where a full antenna spectrum is reconstructed, are shown confirming the same behavior found for a single toroidal mode results in Bertelli et al Nucl. Fusion, 54 083004, 2014, namely, a strong transition to higher SOL power losses (driven by the RF field) has been found when the FW cut-off is removed from in front of the antenna by increasing the edge density. Additionally, full wave simulations have been extended for "conventional" tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for C-Mod and EAST, which operate in the minority heating regime unlike NSTX/NSTX-U and DIII-D, which operate in the mid/high harmonic regime.

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Section: Discussionsupporting

confidence: 89%

Section: D Aorsa Rusults For Nstxmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes^*

et al. 2015

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“…High Harrmonic Fast Wave(HHFW) current drive in frequency range of (ω ci ≪ ω ≪ ω lh ) was suggested in 1995 [2] and it was observed that the current drive is in well agreement with the theory and simulation via MSE measurement. [3] The fast wave close to LHR(Lower Hybrid Resonance) with harmonic number about 20-40 (ω ci ≪ ω < lh ) has beenrecently suggested for off-axis current drive. And it is planned to confirm the theory in KSTAR and DIIID.…”

Section: Introductionmentioning

confidence: 99%

A current drive by using the fast wave in frequency range higher than two timeslower hybrid resonance frequency on tokamaks

Kim

Hwang²,

Jeong³

et al. 2017

EPJ Web Conf.

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Abstract.An efficient current drive scheme in central or off-axis region is required for the steady state operation of tokamak fusion reactors. The current drive by using the fast wave in frequency range higher than two times lower hybrid resonance (w>2wlh) could be such a scheme in high density, high temperature reactor-grade tokamak plasmas. First, it has relatively higher parallel electric field to the magnetic field favorable to the current generation, compared to fast waves in other frequency range. Second, it can deeply penetrate into high density plasmas compared to the slow wave in the same frequency range. Third, parasitic coupling to the slow wave can contribute also to the current drive avoiding parametric instability, thermal mode conversion and ion heating occured in the frequency range w<2wlh. In this study, the propagation boundary, accessibility, and the energy flow of the fast wave are given via cold dispersion relation and group velocity. The power absorption and current drive efficiency are discussed qualitatively through the hot dispersion relation and the polarization. Finally, those characteristics are confirmed with ray tracing code GENRAY for the KSTAR plasmas.

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“…This requires good coupling of the RF power to the core plasma with minimal deposition in the edge region to avoid erosion on the antenna, wall and limiters [e.g., 1 -3], as well as in the divertor scrape off regions [4,5]. Under high-harmonic fast wave (HHFW) heating conditions, the GENRAY [6] and AORSA [7] RF wave models show that even at the lowest toroidal wavenumbers of interest, k φ ~ 3 m -1 , the waves entering the core plasma are damped in about half an orbit around the machine, and wave fields are very low near the center stack [8,9]. Since single-pass damping is very large, edge power loss must occur prior to the fast waves entering the last closed flux surface (LCFS).…”

Section: Introductionmentioning

confidence: 99%

Recent Fast Wave Coupling and Heating Studies on NSTX, with Possible Implications for ITER

Hosea¹,

Bell²,

Feibush³

et al. 2009

AIP Conference Proceedings

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Abstract. The goal of the high harmonic fast wave (HHFW) research on NSTX is to maximize the coupling of RF power to the core of the plasma by minimizing the coupling of RF power to edge loss processes. HHFW core plasma heating efficiency in helium and deuterium L-mode discharges is found to improve markedly on NSTX when the density 2 cm in front of the antenna is reduced below that for the onset of perpendicular wave propagation (n onset ∝ B*k || 2 /ω). In NSTX, the observed RF power losses in the plasma edge are driven in the vicinity of the antenna as opposed to resulting from multi-pass edge damping. PDI surface losses through ion-electron collisions are estimated to be significant. Recent spectroscopic measurements suggest that additional PDI losses could be caused by the loss of energetic edge ions on direct loss orbits and perhaps result in the observed clamping of the edge rotation. Initial deuterium H-mode heating studies reveal that core heating is degraded at lower k φ (-8 m -1 relative to 13 m -1 ) as for the Lmode case at elevated edge density. Fast visible camera images clearly indicate that a major edge loss process is occurring from the plasma scrape off layer (SOL) in the vicinity of the antenna and along the magnetic field lines to the lower outer divertor plate. Large type I ELMs, which are observed at both k φ values, appear after antenna arcs caused by precursor blobs, low level ELMs, or dust. For large ELMs without arcs, the source reflection coefficients rise on a 0.1 ms time scale, which indicates that the time derivative of the reflection coefficient can be used to discriminate between arcs and ELMs.

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Spectral effects on fast wave core heating and current drive

Cited by 38 publications

References 24 publications

Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes^*

Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes^*

A current drive by using the fast wave in frequency range higher than two timeslower hybrid resonance frequency on tokamaks

Recent Fast Wave Coupling and Heating Studies on NSTX, with Possible Implications for ITER

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Spectral effects on fast wave core heating and current drive

Cited by 38 publications

References 24 publications

Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes*

Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes*

A current drive by using the fast wave in frequency range higher than two timeslower hybrid resonance frequency on tokamaks

Recent Fast Wave Coupling and Heating Studies on NSTX, with Possible Implications for ITER

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Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes^*

Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes^*