Stochastic particle acceleration and statistical closures

Technical Report · Tue Oct 01 00:00:00 EDT 1985

DOI:https://doi.org/10.2172/5111904· OSTI ID:5111904

Dimits, A M; Krommes, J A

In a recent paper, Maasjost and Elsasser (ME) concluded, from the results of numerical experiments and heuristic arguments, that the Bourret and the direct-interaction approximation (DIA) are ''of no use in connection with the stochastic acceleration problem'' because (1) their predictions were equivalent to that of the simpler Fokker-Planck (FP) theory, and (2) either all or none of the closures were in good agreement with the data. Here some analytically tractable cases are studied and used to test the accuracy of these closures. The cause of the discrepancy (2) is found to be the highly non-Gaussian nature of the force used by ME, a point not stressed by them. For the case where the force is a position-independent Ornstein-Uhlenbeck (i.e., Gaussian) process, an effective Kubo number K can be defined. For K << 1 an FP description is adequate, and conclusion (1) of ME follows; however, for K greater than or equal to 1 the DIA behaves much better qualitatively than the other two closures. For the non-Gaussian stochastic force used by ME, all common approximations fail, in agreement with (2).

• Research Organization: Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
• DOE Contract Number: AC02-76CH03073
• OSTI ID: 5111904
• Report Number(s): PPPL-2259; ON: DE86002363
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
PLASMA
FOKKER-PLANCK EQUATION
STOCHASTIC PROCESSES
ACCELERATION
MAGNETIC FIELD CONFIGURATIONS
MATHEMATICAL MODELS
ONE-DIMENSIONAL CALCULATIONS
DIFFERENTIAL EQUATIONS
EQUATIONS
PARTIAL DIFFERENTIAL EQUATIONS
700105* - Fusion Energy- Plasma Research- Plasma Kinetics-Theoretical- (-1987)