Presentation on theme: "Magnetic Structures in Electron-scale Reconnection Domain Ilan Roth Space Sciences UC Berkeley, CA Thanks: Forrest Mozer Phil Pritchett Dynamical Processes."— Presentation transcript:
Magnetic Structures in Electron-scale Reconnection Domain Ilan Roth Space Sciences UC Berkeley, CA Thanks: Forrest Mozer Phil Pritchett Dynamical Processes in Space Plasmas Eyn Bokkek, Israel, 10-17 April 2010
Fundamental plasma processes with global implications may occur in a narrow layer Magnetic Reconnection Magnetic shears - electron dominated region What can we learn about electron scale structures without (full) simulations?
Collective plasma scales determine the different (nested) layers: Outer: - Hall effect – ions decouple from B Intermediate: e - inertia (pressure) Inner: break(s) the e - Innermost: frozen-in condition Main purpose: assessing the non ideal effects of Ohms Law Environment: electron (current) velocity >> mass velocity
Two Fluid: coupling (B,v) “Ion” fluid Electron fluid
Sheared field, Inhomogeneous Plasma General coupling between Shear Alfven Compressional Alfven Slow Magneto-Acoustic modified on short scales by (mainly) electron effects
Two (extreme) approaches Lowest approximation of the electron dynamics + follow ion dynamics Lowest approximation of the ion dynamics + follow electron dynamics
A. Faraday and Ohm’s law couple magnetic and velocity fields MHD: Magnetic field is frozen in the fluid drift
Magnetic field – fictitious diagram of lines in R 3 satisfying specific rules. MHD – approximate description of magnetic field motion in a plasma fluid. Knot - closed loop of a non-self-intersecting curve, transformed via continuous deformation of R 3 upon itself, following laws of knot topology - pushed smoothly in the surrounding viscous fluid, without intersecting itself (stretching or bending). MHD field evolves as a topological transformation of a knot. MHD dynamics forms equivalent knot configurations with a set of knot invariants.
All KNOT deformations can be reduced to a sequence of Reidemeister “ moves ” : (I) twist (II) poke, and (III) slide. Type 1Type 2 Type 3 Knot topology described through knot diagrams
Reidemeister moves preserve several invariants of the knot or link represented by their diagram - topological information. MHD invariants: (cross) helicity, generalized vorticity, Ertel,… Every knot can be uniquely decomposed as a knot sum of prime knots, which cannot themselves be further decomposed - Schubert (1949)
Prime knots Characterization based on crossing number – Tait 1877
Flux-rope is a KNOT MHD Turbulence forms a LINK- Collection of knots Reconnection is NOT a KNOT: it forms a KNOT SUM HELIOSPHERE
MHD (KNOT) can be broken via several physical processes Various physical regions Reconnection: topological transition Diffusion: violation of frozen–in condition Dissipation: conversion of em energy (no consensus on definitions)
Parallel electric field is observed in tandem with density gradients Localized electric field over scale ≤ d e =c/ω e – electron inertia effect? Mozer +, 2005
Electron diffusion region: filamentary currents on scale ≤ d e =c/ω e – dissipation region due to electron inertia effect? ELECTRON PHYSICS COVERS LARGE SPATIAL SCALES.
Electron diffusion found NOT at the null of magnetic field: β<1 Localized electric field – scale – electron inertia effect?
Asymmetric Simulation – Pritchett, 2009 Violation of electron frozen-in condition Elongated Electron Diffusion regions
E. Kinetic, incompressible, inhomogeneous plasma Attico +, 2002
SUMMARY A. MHD satisfies the axioms of knot theory – both evolve preserving various invariants. Knot sum is equivalent to violation of frozen-in condition. B. Density gradients/dips, compressibility, and thermal effects may have a significant effect on the electron vorticity, which determines the slipping of the magnetic field with respect to the electrons. These effects modify the structure of the magnetic field on the short-scale, forming current filaments, parallel electric fields, which violate the frozen-in condition and contribute to electron heating. These regions are ubiquitous and are observed outside of the x-points in the reconnection domain.