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SUMMARY:Kinetic effects in collisionless and turbulent space plasmas: 'in 
 situ' data and Vlasov simulations - Dr. Denise Perrone (ASI\, Rome)
DTSTART:20191118T140000Z
DTEND:20191118T150000Z
UID:TALK129205@talks.cam.ac.uk
CONTACT:Chris Hamilton
DESCRIPTION:Living on Earth\, and thanks to the support of many space miss
 ions\, we have the unique opportunity\nto analyse directly the features of
  the dynamical behaviour of a natural plasma: the solar wind. A\npuzzling 
 aspect of solar-wind dynamics consists in the empirical evidence that it i
 s hotter than\nexpected for an adiabatic expanding gas. Understanding the 
 physical mechanisms of dissipation\,\nand the related heating\, in such tu
 rbulent collision-free system represents nowadays one of the key\nissues o
 f plasma physics but also for thermodynamics in general. Plasma turbulence
  is a challenging\nproblem\, involving a variety of complex phenomena: the
  energy transferred towards smaller scales\nby turbulence produces localiz
 ed regions (coherent structures) where dissipation increases\, and\npartic
 le distribution functions are strongly distorted. The absence of an equili
 brium attractor leaves\nthe plasma state free to explore the dual spatial-
 velocity phase space. In this scenario\, the use of\nboth spacecraft measu
 rements and kinetic numerical simulations becomes crucial.\n\nHere\, a nov
 el theory of space plasma turbulence is described to investigate the possi
 bility of a\nvelocity-space cascade\, by means of a three-dimensional Herm
 ite decomposition applied to both\nnumerical and ‘in situ’ measurement
 s. A broad-band\, power-law Hermite spectrum for the velocity\nspace fluct
 uations of the ion velocity distribution is recovered. Moreover\, by using
  high-time\nresolution magnetic field data of multi-point measurements\, t
 he nature of the turbulent\nfluctuations close to the ion scales is invest
 igated. However\, due to the limitation on in-situ particle\nmeasurements\
 , a support from self-consistent fully nonlinear Vlasov models is needed. 
 High\nresolved hybrid Vlasov-Maxwell simulations have been used to investi
 gate the details of the strong\ndeformation of the ion distribution functi
 on. The phase-space cascade might be of general relevance\nfor the nonline
 ar dynamics of a weakly-collisional plasma in a wide variety of conditions
 .
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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