Toroidal ion temperature gradient-driven weak turbulence

Journal Article · Thu Aug 01 04:00:00 EDT 1991 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.859660· OSTI ID:5459866

Mattor, N ^[1]

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1. Culham Laboratory, Abingdon, Oxfordshire OX14 3DB, England (GB)

In this paper, a theory of toroidal ion temperature gradient-driven weak turbulence near the threshold is presented. The model considers gyrokinetic ions and adiabatic electrons in toroidal geometry. The linear theory considers modes with {ital k}{sub {theta}}{rho}{sub {ital i}}{similar to}{ital O}(1) generally not considered in toroidal theories, giving a toroidal threshold regime dominated by transit resonances as opposed to the more usually considered drift resonances, and with a stability threshold of {eta}{sup tor}{sub thresh}{congruent}1+2{epsilon}{sub {ital n}}(2/{tau}+1/(1+{ital {cflx s}})). It is shown that when 0{lt}{eta}{sub {ital i}}{minus}{eta}{sup tor}{sub thresh}{lt}2(1+1/{tau}){sup 1/2} {times}{ital L}{sub {ital n}}/({ital RL}{sub {ital T}}){sup 1/2} then 0{lt}{gamma}{lt}{omega}{sub {ital r}}, and a weak turbulence expansion can be used to treat the nonlinearity. The instability is saturated via nonlinear ion resonance, and it is shown that this nonlinear process transfers energy directly from the waves to the ion distribution function, and does not conserve wave energy. The saturated spectrum is calculated, and the resulting ion thermal conductivity is found to be {chi}{sub {ital i}}=(1+1/{tau}){sup 1/2}(({eta}{sub {ital i}}{minus}{eta}{sup tor}{sub th})/{eta}{sub {ital i}}) (({ital L}{sub {ital T}}){sup 1/2}/{ital R}{sup 3/2}){rho}{sup 3}{sub {ital i}}{Omega}{sub {ital i}}, which is smaller than typical mixing length estimates by a factor of about {ital L}{sub {ital T}}/{ital R}, but in the range of tokamak observations. The diffusive nature of the transport requiring a short radial step size is reconciled with the broad radial extent of the toroidally coupled linear modes by postulating that it is the nonlinear beat wave between linear modes not the radial width of a single linear mode that determines the step length appropriate for transport.

• OSTI ID: 5459866
• Journal Information: Physics of Fluids B; (United States), Journal Name: Physics of Fluids B; (United States) Vol. 3:8; ISSN 0899-8221; ISSN PFBPE
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700108* -- Fusion Energy-- Plasma Research-- Wave Phenomena
ANNULAR SPACE
CLOSED CONFIGURATIONS
CLOSED PLASMA DEVICES
CONFIGURATION
HOT PLASMA
INSTABILITY
ION TEMPERATURE
MAGNETIC FIELD CONFIGURATIONS
PLASMA
PLASMA DRIFT
SPACE
THERMONUCLEAR DEVICES
TOKAMAK DEVICES
TOROIDAL CONFIGURATION
TURBULENCE
WAVE PROPAGATION