BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Physics of Velocity and Magnetic Shears in Toroidal Geometries - M
 ingyun Cao (University of California\, San Diego)
DTSTART:20240517T103000Z
DTEND:20240517T113000Z
UID:TALK216916@talks.cam.ac.uk
DESCRIPTION:Velocity and magnetic shears are ubiquitous in tokamaks. Both 
 of them play critical roles in plasma dynamics and confinement performance
  by affecting the coherence of fluctuations in space and time. In the past
  few decades\, especially with the recent development of large-scale gyrok
 inetic numerical simulations\, there has been a growing understanding of t
 he shears in tokamaks. &nbsp\;However\, theoretical discussions\, which tr
 eat magnetic shear and E&times\;B shear in tokamaks on an equal footing\, 
 have rarely been done.\nIn this talk\, I will start from the idea of reson
 ance and demonstrate the analogies between velocity and magnetic shear. Sh
 earing coordinates\, introduced to eliminate the parallel gradient operato
 r\, serve as a useful tool to describe fluctuations in shear. With the ado
 ption of shearing coordinates\, we lose the normal mode description and in
 stead gain a 'quasi-mode'&mdash\;an effective wave packet of spatially loc
 alized resistive interchange modes. Compared with resistive interchange mo
 de\, quasi-mode exhibits a broader mode structure\, thus enhancing mixing.
  In addition\, quasi-mode has many resemblances to the ballooning mode\, w
 hich is a typical plasma instability arising from the toroidal geometry of
  tokamaks. Therefore\, quasi-mode could be a bridge between cylindrical an
 d toroidal geometries\, and studying it helps us better understand the tor
 oidicity effects in tokamaks. The talk ends with two traditional theoretic
 al methods for ballooning mode studies: the Bloch eigenmode equation and t
 he ballooning mode representation.\nThis talk is an instructive resource f
 or understanding the basics of shearing dynamics and toroidicity effects i
 n tokamaks.
LOCATION:Seminar Room 2\, Newton Institute
END:VEVENT
END:VCALENDAR