A one-dimensional model for lower-hybrid current drive including perpendicular dynamics

Fuchs, V.; Cairns, R. A.; Shoucri, M.; Hizanidis, Kyriakos; Bers, A.

doi:10.1063/1.865318

Cited by 53 publications

(41 citation statements)

References 2 publications

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“…Here, (0/8), is the linearized collision operator for electrons slowing down and pitch angle scattering in (u,v±) space, as given in various references (see e.g. [3]). The collisional contribution to radial transport has a negligible effect on the confinement of fast electrons and can be ignored; hence the collision operator does not act on the p dependence of f. The quasilinear operator (see Appendix A) is 8 1 8 8 8…”

Section: The Fokker-planck Equationmentioning

confidence: 99%

Fast electron transport in lower-hybrid current drive

Küpfer

Bers

1991

Physics of Fluids B: Plasma Physics

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The quasilinear Fokker–Planck formulation is generalized for lower-hybrid current drive to include the wave-induced radial transport of fast electrons. Toroidal ray tracing shows that the wave fields in the plasma develop a large poloidal component associated with the upshift in k∥ and the filling of the ‘‘spectral gap.’’ These fields lead to an enhanced radial E×B drift of resonant electrons. Two types of radial flows are obtained: an outward convective flow driven by the asymmetry in the poloidal wave spectrum, and a diffusive flow proportional to the width of the poloidal spectrum. Numerical results relevant to Alcator C [Phys. Rev. Lett. 53, 450 (1984)] and JT-60 [Nucl. Fusion 29, 1815 (1989)] are presented; they show that the radial convection velocity has a broad maximum of nearly 1 m/sec and is independent of the amplitude of fields. In both cases, the radial diffusion is found to be highly localized near the magnetic axis. For JT-60, the peak of the diffusion profile can be quite large, nearly 1 m2/sec.

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Section: The Fokker-planck Equationmentioning

confidence: 99%

Fast electron transport in lower-hybrid current drive

Küpfer

Bers

1991

Physics of Fluids B: Plasma Physics

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“…Fokker-Planck equation, 3 and then make comparisons to results from the full numerical solution of the Fokker-Planck-equation.…”

Section: Intoductionmentioning

confidence: 99%

The anomalous Doppler instability during lower-hybrid current drive

Luckhardt

Bers

Fuchs

et al. 1987

The Physics of Fluids

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The anomalous Doppler instability is investigated for two-dimensional velocity distributions f(v∥,v⊥) appropriate for lower-hybrid current drive. In this case, in contrast to the runaway electron problem, this mode becomes unstable at high density when the ratio ω2pe/ ω2ce is sufficiently large. Increasing the maximum velocity v2 of the rf (radio-frequency) plateau, v1≤v∥ ≤v2, is also a destabilizing influence. In this paper expressions are given for the growth rate of the electrostatic waves obeying the dispersion relation ω=ωpe (1+ω2pe/ ω2ce)−1/2 k∥/k, employing both analytic expressions for f(v∥,v⊥) and numerical solutions for f from the two-dimensional Fokker–Planck equation. The analytical and numerical results are in close agreement.

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“…The effect of enhanced perpendicular temperature of the tail is modeled using the formalism of Fuchs, et al [18] A direct electron tail loss mechanism due to radial diffusion was included and was modeled with a phenomenological energy dependent confinement time [19] of the form -r-= rof, where ro has a value comparable to the bulk electron energy confinement time rEe in LHCD plasmas. This form of the electron tail confinement time reflects the notion that higher energy electrons experience less radial transport [20].…”

Section: Numerical Modelingmentioning

confidence: 99%

Energy confinement studies of lower hybrid current driven plasmas in the Alcator C tokamak

et al. 1987

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ABSTRACT. Energy confinement is studied in lower hybrid current driven (LHCD) plasmas in Alcator C in the density range ii = (1-8) x 1013 cm-3 . In LHCD plasmas, the stored energy in the electron tail Wail can be a significant fraction of the total stored energy W"*, especially at lower densities. At sufficiently low densities, the energy confinement time of the high energy electrons is expected to become shorter than their collisional energy slowing down time, and direct energy losses from the electron tail can become important in the overall power balance. The global energy confinement time, defined as rE** = W**t/Ptot, is found to be comparable to or exceed that in ohmically heated (OH) plasmas at low densities n, < 3 x 1013 cm-3 , where a steady state current can be maintained with * present address : University of Texas, Austin, Texas, U.S.A. 1 relatively low rf power. However, at higher densities where substantially more rf power is needed (relative to the ohmic power required to maintain a similar plasma), a deterioration of rtot relative to ohmic confinement, similar to that predicted by the neutral beam heated L-mode scaling, is observed.Theoretical modeling with the aid of a ray tracing-Fokker Planck-transport code suggests that the deteriorated confinement in this high density, high power regime may be attributed to an enhanced bulk electron thermal diffusivity. In a combined OH-LHCD plasma, a value of r' greater than the ohmic value is obtained as long as the applied rf power does not significantly exceed the ohmic power.2

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A one-dimensional model for lower-hybrid current drive including perpendicular dynamics

Cited by 53 publications

References 2 publications

Fast electron transport in lower-hybrid current drive

Fast electron transport in lower-hybrid current drive

The anomalous Doppler instability during lower-hybrid current drive

Energy confinement studies of lower hybrid current driven plasmas in the Alcator C tokamak

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