Gyrokinetic simulations of mesoscale energetic particle-driven Alfvenic turbulent transport embedded in microturbulence

Journal Article · Mon Nov 15 00:00:00 EST 2010 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3509106· OSTI ID:21531974

Bass, E M; Waltz, R E ^[1]

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1. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)

Energetic particle (EP) transport from local high-n toroidal Alfven eigenmodes (TAEs) and energetic particle modes (EPMs) is simulated with a gyrokinetic code. Linear and nonlinear simulations have identified a parameter range where the longwave TAE and EPM are unstable alongside the well-known ion-temperature-gradient (ITG) and trapped-electron-mode (TEM) instabilities. A new eigenvalue solver in GYRO facilitates this mode identification. States of nonlinearly saturated local TAE/EPM turbulent intensity are identified, showing a 'soft' transport threshold for enhanced energetic particle transport against the TAE/EPM drive from the EP pressure gradient. The very long-wavelength (mesoscale) TAE/EPM transport is saturated partially by nonlinear interaction with microturbulent ITG/TEM-driven zonal flows. Fixed-gradient-length, nonlinearly saturated states are accessible over a relatively narrow range of EP pressure gradient. Within this range, and in the local limit employed, TAE/EPM-driven transport more closely resembles drift-wave microturbulent transport than 'stiff' ideal MHD transport with a clamped critical total pressure gradient. At a higher, critical EP pressure gradient, fixed-gradient nonlinear saturation fails: EP transport increases without limit and background transport decreases. Presumably saturation is then obtained by relaxation of the EP pressure gradient to near this critical EP pressure gradient. If the background plasma gradients driving the ITG/TEM turbulence and zonal flows are weakened, the critical gradient collapses to the TAE/EPM linear stability threshold. Even at the critical EP pressure gradient there is no evidence that TAE/EPM instability significantly increases transport in the background plasma channels.

• OSTI ID: 21531974
• Journal Information: Physics of Plasmas, Vol. 17, Issue 11; Other Information: DOI: 10.1063/1.3509106; (c) 2010 American Institute of Physics; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALFVEN WAVES
CHARGED-PARTICLE TRANSPORT
EIGENVALUES
ION TEMPERATURE
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
PLASMA
PLASMA INSTABILITY
PLASMA PRESSURE
PLASMA SIMULATION
PRESSURE GRADIENTS
TEMPERATURE GRADIENTS
TRAPPED ELECTRONS
TURBULENCE
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
FLUID MECHANICS
HYDRODYNAMICS
HYDROMAGNETIC WAVES
INSTABILITY
LEPTONS
MECHANICS
RADIATION TRANSPORT
SIMULATION