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SUMMARY:Characterization of formation and stability of impurity ‘snakes
 ’ in tokamak plasmas
DTSTART:20120709T140000
DTEND:20120709T150000
DTSTAMP:20260428T073519Z
UID:0099dbf923cbede37a61a1d5f51d716352a0d3d700f3c6c2e8a4c816
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Luis F. Delgado-Aparicio\, Princeton Plasma Physics Labor
 atory\, Princeton\, USA\nAlthough (m\,n)=(1\,1) “snake” modes were di
 scovered at JET more than 25 years ago\, there are still basic unanswered 
 questions regarding their formation\, stability\, and superb particle conf
 inement\, shown by surviving tens to hundreds of sawtooth cycles. A novel 
 suite of spectroscopic imaging diagnostics have facilitated the determinat
 ion of the perturbed radiated power density\, impurity density and tempera
 ture oscillations inside the (1\,1) mode with unprecedented temporal and s
 patial resolution\, making it possible to infer\, for the first time\, the
  perturbed profiles of the impurity density\, plasma pressure\, Zeff\, and
  resistivity at the center of these helical modes [1]. These new results i
 ndicate that snakes form as an asymmetry in the impurity ion density that 
 undergoes a seamless transition from a small helically displaced kink dens
 ity to a large crescent-shaped helical island structure inside q < 1\, wit
 h a regularly sawtoothing core [1\,2]. These new high-resolution observati
 ons show details of their evolution and the accompanying sawtooth oscillat
 ions that suggest important differences between the density and temperatur
 e dynamics\, ruling out a purely pressure-driven process [2]. The observed
  differences are consistent with the results of nonlinear 3D MHD simulatio
 ns that evolve plasma density and temperature separately.\n\n[1] L. Delgad
 o-Aparicio\, et. al.\, MIT-PSFC/JA-11-28 report. Rev. Sci. Instrum.\, 83\,
  in-print\, (2012).\n[2] L. Delgado-Aparicio\, et. al.\, submitted to Phys
 . Rev. Letters\, (2012).
LOCATION:PPB 019
STATUS:CONFIRMED
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