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PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
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UID:UW-Physics-Event-7896
DTSTART:20220912T170000Z
DURATION:PT1H0M0S
DTSTAMP:20260414T234051Z
LAST-MODIFIED:20220909T182609Z
LOCATION:1610 Engineering Hall
SUMMARY:Formation and Particle Acceleration in Large-Scale Diamagnetic
  Cavities at the Boundary of Earth’s Magnetic Shield\, Plasma Physic
 s (Physics/ECE/NE 922) Seminar\, Katariina Nykyri\, Embry-Riddle Unive
 rsity
DESCRIPTION:Earth’s magnetic field resembles that of the bar-magnet 
 where magnetic field converges (diverges) toward northern (southern) h
 emisphere at the high-latitudes creating two funnel-like structures ca
 lled geomagnetic cusps. Because the magnetic field around the cusps ro
 tates by 360 degrees\, there always exist regions where geomagnetic fi
 eld and interplanetary magnetic field (IMF) are anti-parallel in the v
 icinity of the cusps\, leading to magnetic reconnection if plasma flow
  is sub-Alfvenic along the k-vector of the tearing instability. On the
  other hand\, the magnetosheath flow is perpendicular to cusp field bo
 th at the dawn and dusk sectors of the high-altitude cusps\, leading t
 o Kelvin-Helmholtz Instability and associated secondary processes.<br>
 
\n           Cluster and MMS spacecraft observations have revealed th
 at magnetic reconnection (both at the high- and the low-latitudes) can
  create large-scale diamagnetic cavities in the high-latitude magnetos
 phere where particles can be accelerated to 100s of keV in the reconne
 ction quasi-potential. The acceleration mechanism creates strongly per
 pendicular pitch angle distributions for ions and electrons\, likely c
 ontributing to the source for the observed  ion temperature anisotropy
  in the high-latitude magnetosphere. Recently\, 4 MMS spacecraft flew 
 through a dusk- sector southern hemispheric diamagnetic cavity observi
 ng strong ULF wave activity\, driven by the drift-mirror instability\,
  at the edge of the cavity. The high-energy electrons within these wav
 e field depressions showed counter-streaming pitch angle distributions
  while ions remained trapped. MMS spacecraft also have detected high-e
 nergy trapped electrons and occasionally parallel streaming high-energ
 y ions within Kelvin-Helmholtz waves at high-latitudes\, in the vicini
 ty of the Southern hemispheric dawn-sector cusp.<br>
\n           In t
 his talk I demonstrate the formation mechanism of these diamagnetic ca
 vities\, show the observed and simulated signatures of particle accele
 ration\, as well as discuss the possible physical mechanisms leading t
 o their escape from the cavities and their subsequent faith and conseq
 uences for magnetospheric energy and mass budget\, and on the origin o
 f seed population of the radiation belts. <br>
\nAs cusp-like structur
 es are universal\, these cavity-associated acceleration mechanisms may
  be important also for plasma energization in other systems\, e.g.\, i
 n the atmospheres of magnetized stars. The ~four-orders of magnitude e
 nergy increase\,  associated with this process\,  may also be importan
 t for plasma energization in laboratory plasmas with cusp-like configu
 rations.<br>
\n
URL:https://www.physics.wisc.edu/events/?id=7896
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