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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:12
UID:UW-Physics-Event-8987
DTSTART:20241202T180500Z
DTEND:20241202T190000Z
DTSTAMP:20260413T184739Z
LAST-MODIFIED:20241122T195837Z
LOCATION:1610 Engineering Hall
SUMMARY:Tearing-mediated reconnection in magnetohydrodynamic poorly io
 nized plasmas\, Plasma Physics (Physics/ECE/NE 922) Seminar\, Elizabet
 h Tolman\, Flatiron Institute
DESCRIPTION:Many plasma environments\, such as star-forming molecular 
 clouds\, the solar chromosphere\, and the diffuse interstellar medium\
 , are poorly ionized and threaded by dynamically important magnetic fi
 elds. We use theory and computation to study tearing-mediated reconnec
 tion in such poorly ionized systems. In this work\, we focus on the on
 set and linear evolution of this process. In poorly ionized plasmas\, 
 magnetic nulls on scales below v<sub>A\,n0</sub>/𝜈
\n<sub>ni0</sub>
 \, with v<sub>A\,n0</sub> the neutral Alfvén speed and 𝜈
\n<sub>ni
 0</sub> the neutral–ion collision frequency\, will self-sharpen via 
 ambipolar diffusion. This sharpening occurs at an increasing rate\, in
 hibiting the onset of reconnection. Once the current sheet becomes thi
 n enough\, however\, ions decouple from neutrals and the thinning of t
 he CS slows\, allowing the onset of tearing in a time of order 𝜈
\n
 <sub>ni0</sub> . We find that the wavelength and growth rate of the mo
 de that first disrupts the forming sheet can be predicted from a poorl
 y ionized tearing dispersion relation\; as the plasma recombination ra
 te increases and ionization fraction decreases\, the growth rate becom
 es an increasing multiple of 𝜈
\n<sub>ni0</sub> and the wavelength 
 becomes a decreasing fraction of v<sub>A\,n0</sub>/𝜈
\n<sub>ni0</su
 b>. After reconnection onsets in a current sheet\, the system enters a
  nonlinear phase characterized by a stochastic plasmoid chain\, but th
 e characteristics of this chain differ from those of a stochastic plas
 moid chain in fully ionized plasma. The plasma in the plasmoids is cha
 racterized by an ionization fraction which is much larger than that of
  the background plasma. Our results could have significant implication
 s for understanding of several important astrophysical processes\, inc
 luding the transport of cosmic rays in the interstellar medium.
URL:https://www.physics.wisc.edu/events/?id=8987
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