Plasma Astrophysics And Space Physics

pp 171-182

Solar Flare Phenomena As Phase Transition Caused By Frustration Of Current Percolation

  • L. A. Pustil’nikAffiliated withIsrael Cosmic Ray Center, Tel-Aviv Univ., Sea of Galilee Astrop. Obs., Jordan Valley College

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We present analysis of flare process as ”phase transition” phenomena caused by frustration of current percolation in turbulent current sheet. We show that numerous plasma instabilities in the sheet will form random resistors network with ”bad resistors”-turbulent domains and ”good resistors”-normal plasma domains. We show that current percolation in random inhomogeneous turbulent current sheet like to another percolated systems is able to produce phase transition with drastic change of global properties of system as whole (conductivity, heat-conductivity, elasticity,) on the threshold value of critical density of ”bad” elements (p = p c ). Another property of solar flares, what may be understood on the base of percolation approach is observed universal power dependence of frequency of flares and microflares (elementary events-spikes) on their amplitude: N W W -k . It may be explained as natural sequence of universal power dependence of clusters’ masses in percolated systems on their sizes. The slope of resulted spectra is determined by the fractal dimension of clusters and depends on feedback between current propagation and turbulence generation. We show that percolation approach allow to explain phenomena of preflare bursts-precursors observed in radio and hard X-ray. It may be understood as results of pre-catastrophic lose of elasticity of system to small disturbance on the percolation threshold, with formation of short life nuclear of ”new phase”.