Thermostatted delta f

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The delta f simulation method is revisited. Statistical coarse-graining is used to rigorously derive the equation for the fluctuation delta f in the particle distribution. It is argued that completely collisionless simulation is incompatible with the achievement of true statistically steady states with nonzero turbulent fluxes because the variance of the particle weights w grows with time. To ensure such steady states, it is shown that for dynamically collisionless situations a generalized thermostat or W-stat may be used in lieu of a full collision operator to absorb the flow of entropy to unresolved fine scales in velocity space. The simplest ... continued below

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539 Kilobytes pages

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Krommes, J.A. January 18, 2000.

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Description

The delta f simulation method is revisited. Statistical coarse-graining is used to rigorously derive the equation for the fluctuation delta f in the particle distribution. It is argued that completely collisionless simulation is incompatible with the achievement of true statistically steady states with nonzero turbulent fluxes because the variance of the particle weights w grows with time. To ensure such steady states, it is shown that for dynamically collisionless situations a generalized thermostat or W-stat may be used in lieu of a full collision operator to absorb the flow of entropy to unresolved fine scales in velocity space. The simplest W-stat can be implemented as a self-consistently determined, time-dependent damping applied to w. A precise kinematic analogy to thermostatted nonequilibrium molecular dynamics (NEMD) is pointed out, and the justification of W-stats for simulations of turbulence is discussed. An extrapolation procedure is proposed such that the long-time, steady-state, collisionless flux can be deduced from several short W-statted runs with large effective collisionality, and a numerical demonstration is given.

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539 Kilobytes pages

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INIS; OSTI as DE00750255

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  • Other Information: PBD: 18 Jan 2000

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  • Report No.: PPPL--3419
  • Grant Number: AC02-76CH03073
  • DOI: 10.2172/750255 | External Link
  • Office of Scientific & Technical Information Report Number: 750255
  • Archival Resource Key: ark:/67531/metadc710794

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  • January 18, 2000

Added to The UNT Digital Library

  • Sept. 12, 2015, 6:31 a.m.

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  • April 15, 2016, 7:28 p.m.

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Krommes, J.A. Thermostatted delta f, report, January 18, 2000; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc710794/: accessed August 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.