Resonant Drift-Wave Coupling Modified by Nonlinear Separatrix Dissipation

Kabant︠s︡ev, A. A.; O’Neil, T. M.; Tsidulko, Yu. A.; Driscoll, C. F.

doi:10.1103/physrevlett.101.065002

Cited by 8 publications

(12 citation statements)

References 11 publications

(14 reference statements)

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“…12, which sketches the radial diffusion coefficient versus collision frequency. We emphasize that this perspective is supported by quantitative experiments (Kabantsev and Driscoll 2002;2006;Kabantsev et al 2008 and references therein), in agreement with detailed theory and targeted simulations (Hilsabeck and O'Neil 2003;Dubin 2008;Dubin et al 2010;. This research enabled identification of the different regimes characterized by collisional energy spreading W c , ruffle amplitude φ m , and fluctuation amplitude φ(t); and it clarified the connection to kinetic processes at low rigidity R. This broader perspective may aid in interpretation of numerical simulations developed for stellarator geometry (Beidler et al 2011), where multiple processes combine.…”

Section: Low-collisionality Enhancementsupporting

confidence: 53%

“…The experiments utilize a cylindrical Penning-Malmberg trap to confine quiescent, low-collisionality pure electron plasmas (Kabantsev and Driscoll 2002;2006;Kabantsev et al 2008). Electrons are confined radially by a nominally uniform axial magnetic field Bẑ, with 0.04 6 B 6 2 T; and are confined axially by voltages V c = −100 V on end cylinders of radius R W = 3.5 cm.…”

Section: Methodsmentioning

confidence: 99%

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Neoclassical transport processes in weakly collisional plasmas with fractured velocity distribution functions

et al. 2014

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Ripples in magnetic or electrostatic confinement fields give rise to trapping separatrices, and conventional neoclassical transport theory describes the collisional trapping/detrapping of particles with fractured distribution function. Our experiments and novel theory have now characterized a new kind of neoclassical transport processes arising from chaotic (nominally collisionless) separatrix crossings, which occur due to E × B plasma rotation along θ−ruffled or wave-perturbed separatrices. This chaotic neoclassical transport becomes dominant at low collisionality when the collisional spreading of particle energy during the dynamical period is less than the separatrix energy ruffle.

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Section: Low-collisionality Enhancementsupporting

confidence: 53%

Section: Methodsmentioning

confidence: 99%

Neoclassical transport processes in weakly collisional plasmas with fractured velocity distribution functions

et al. 2014

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“…Further, one would reasonably expect that separatrix-induced TPDM damping γ 1a could significantly affect the time evolution of the decay instability. Figure 10 shows the time evolution of mode amplitudes A 2 and A 1a when A 2 is driven to large amplitude and f 1a is tuned for resonance [8]. The TPDM is observed to grow from noise, then saturate and oscillate at an amplitude similar to the depleted A 2 .…”

Section: Resonant Wave-wave Couplings With Separatrix Dissipation (5)mentioning

confidence: 85%

“…The five effects described here include bulk particle transport [1,2,3,4,5], damping of drift [6] and Langmuir [7] waves, and modified nonlinear wave-wave couplings [8]. Experiments and theory distinguish traditional collisional effects from the novel chaotic effects, with chaotic effects dominating in regimes of low collisionality.…”

Section: Introductionmentioning

confidence: 99%

Transport, damping, and wave-couplings from chaotic and collisional neoclassical transport

Driscoll

Kabant︠s︡ev

Dubin

et al. 2013

AIP Conference Proceedings

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Experiments and theory characterize the novel chaotic neoclassical transport scaling as ν 0 c B −1 in contrast to traditional collisional neoclassical transport scaling as ν 1/2 c B −1/2 . This chaotic transport occurs when local trapping separatrices have θ-variations or temporal fluctuations. Experiments observe bulk particle transport, damping of Langmuir waves and diocotron waves, and nonlinear wave-wave couplings. These effects may be important in low-collisionality fusion plasmas.

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“…6 Much additional work then explored and generalized the neoclassical damping and transport. [7][8][9][10][11][12][13] Of course, waves and field asymmetries also produce transport in nonneutral plasmas without separate classes of trapped and passing particles, and in these plasmas the dominant transport mechanism is thought to be resonant particle transport. [14][15][16][17][18][19] As described in the abstract, the purpose of this brief communication is to resolve a point of theoretical confusion introduced in the first theoretical papers on the TPDM.…”

mentioning

confidence: 98%

Particle fluxes through the separatrix in the trapped particle diocotron mode

2011

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In the trapped particle diocotron mode, the trapped particles undergo E Â B drift motion in a uniform B field. Since such a flow is incompressible one is tempted to assume that the trapped particle density is constant along a fluid element. However, this is not the case since there is interchange of trapped and passing particles through the separatrix. This paper shows that a corrected fluid analysis, taking into account the particle flux through the separatrix, reproduces the same trapped particle density perturbation as obtained from the kinetic theory, thereby resolving confusion in earlier papers.Electric and magnetic field inhomogeneities in plasma containment devices often cause particles to be trapped in localized regions, and these trapped particles give rise to a class of low frequency modes of oscillation called trapped particle modes 1 and to the important phenomena of neoclassical transport. 2 Recent work using nonneutral plasmas has provided access to the physics of trapped particle modes and neoclassical transport for a simple geometry and quiescent plasma, where well-controlled comparisons of theory and experiment are possible.Trapped particle diocotron modes (TPDM) are routinely excited on nonneutral plasma columns in which there are classes of trapped and passing particles. 3 To create these classes, the usual Malmberg-Penning trap configuration is modified by applying an azimuthally symmetric potential barrier, the squeeze potential, near the axial mid-point of the column. Particles with relatively low axial velocity are trapped on one side or the other of the barrier, while high velocity particles pass back and forth along the axial magnetic field over the full length of the plasma column.The mode dynamics is easy to understand qualitatively. The mode potential has odd parity in the axial coordinate and produces bounce-average E Â B drift oscillations of the trapped particles that are 180 out of phase on the two sides of the barrier, while the passing particles stream back and forth, partially Debye shielding the perturbation in the trapped particle charge density.A theoretical description of the TPDM was obtained using the Poisson's equation and the drift kinetic equation with a Fokker-Planck (FP) collision operator. 4,5 Experiments had observed damping of the TPDM, and the theory explained the damping as resulting from collisional velocity diffusion at the separatrix between trapped and untrapped particles. Associated with the damping is a neoclassical particle transport. The damping and associated transport also were investigated using numerical simulations. 6 Much additional work then explored and generalized the neoclassical damping and transport. 7-13 Of course, waves and field asymmetries also produce transport in nonneutral plasmas without separate classes of trapped and passing particles, and in these plasmas the dominant transport mechanism is thought to be resonant particle transport. [14][15][16][17][18][19] As described in the abstract, the purpose of this brief communication is to...

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Resonant Drift-Wave Coupling Modified by Nonlinear Separatrix Dissipation

Cited by 8 publications

References 11 publications

Neoclassical transport processes in weakly collisional plasmas with fractured velocity distribution functions

Neoclassical transport processes in weakly collisional plasmas with fractured velocity distribution functions

Transport, damping, and wave-couplings from chaotic and collisional neoclassical transport

Particle fluxes through the separatrix in the trapped particle diocotron mode

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