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VERSION:2.0
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PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:1
UID:UW-Physics-Event-7789
DTSTART:20220715T190000Z
DTEND:20220715T230000Z
DTSTAMP:20260414T113311Z
LAST-MODIFIED:20220713T160149Z
LOCATION:B343 Sterling or https://uwmadison.zoom.us/j/94077711149?pwd=
 VytqYWEzOHpBNnVjL0NNcnYvQ2p1Zz09
SUMMARY:Exploring kinetic physics in space plasmas using PIC simulatio
 ns\, Thesis Defense\, Harsha Gurram\, Physics PhD Graduate Student
DESCRIPTION:This dissertation investigates two major long-standing pro
 blems in space physics with the aid of kinetic simulations. Our first 
 study delves into magnetic reconnection\, a fundamental process in mag
 netized plasmas wherein global magnetic topology is modified and the b
 uilt-up magnetic stress is transformed into plasma flows and heating. 
 This energy conversion process is thought to be an important mechanism
  for particle energization in space. Here\, we analyzed fully kinetic 
 simulation results of magnetic reconnection to study how the released 
 energy and associated signatures propagate away from the reconnection 
 site. In contrast to previous studies\, where\, the Hall magnetic fiel
 d structures were carried away by kinetic Alfv\\'{e}n waves (KAWs). Ou
 r kinetic simulation implemented at a large numerical domain and with 
 open boundary conditions permits large-amplitude SAWs to be excited by
  the reconnection dynamics. Due to the dispersive nature of the KAWs\,
  they eventually get damped\, and SAWs become the main carrier of the 
 energy away from the reconnection site. These reconnection-driven SAWs
  are observed to propagate distances $\\gg 9R_e$ unattenuated carrying
  sufficient energy and may act as a primary energy source to drive the
  white aurora.<br>
\n<br>
\nOur second study examines the effects of C
 oulomb collisions in solar-wind heating. The temperature of the solar 
 wind plasma expanding from the hot solar corona does not decrease with
  the distance as fast as predicted by the adiabatic expansion law. The
  heating of the solar-wind electrons results from the energy exchange 
 of the fast electrons propagating from the corona along the background
  magnetic field (the beam or strahl) and the electrons trapped between
  the electric potential and magnetic mirror walls (the core). The leve
 l of the trapped population is a result of two competing processes—p
 article influx from the streaming population due to pitch-angle scatte
 ring and particle losses through the boundary due to energy diffusion.
  As scattering rates are a free parameter in our study\, we can determ
 ine how the scattering rates affect the electron distributions\, and i
 n turn temperature of the solar wind electrons. Using 1D cylindrical s
 imulations we found the electron temperature profiles scaled with the 
 ratio $\\nu{ee}/\\nu{ei}$\, higher the $\\nu{ee}/\\nu{ei}$ higher the 
 electron temperatures. The dependency of the electron temperatures and
  trapped electron population on $\\nu{ei}/\\nu{ee}$ in the kinetic sim
 ulations implies that the Coulomb collisions have a significant effect
  on the electron temperature profiles as suggested by the collisional 
 model.
URL:https://www.physics.wisc.edu/events/?id=7789
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