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SUMMARY:Overview of I-mode studies on ASDEX Upgrade: access\, confinement 
 properties and turbulence characterization
DTSTART:20170523T103000
DTEND:20170523T113000
DTSTAMP:20260512T232629Z
UID:40cf8fda874194d1d1ebaa7b439efad6a785acd1cf4e788a02ba5fc7
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. T. Happel - Max-Planck-Institut für Plasmaphysik (IPP-Gar
 ching)\, D\nThe I-mode is an improved confinement regime of tokamak plasma
 s where an edge transport barrier is observed in the energy channel but no
 t in the particle transport [1]. This is in contrast to H-mode confinement
 \, which is characterized by transport barriers in both energy and particl
 es. Consequently\, in I-mode the impurity confinement time is low\, which 
 results in low values of the effective charge Zeff. The I-mode can only be
  obtained if the power threshold for H-mode access is kept high\, e.g. by 
 using unfavorable magnetic configurations. After substantial I-mode resear
 ch by the fusion community in the last years\, the mechanism which selecti
 vely reduces only one of the transport channels is still not understood. A
 nother characteristic feature is an instability called the weakly coherent
  mode (WCM)\, which resides in the plasma edge.\n\nAn overview of I-mode s
 tudies performed on the ASDEX Upgrade tokamak is given\, including power t
 hreshold\, pedestal development and confinement properties. Detailed inves
 tigations of turbulence properties in the I-mode edge have been carried ou
 t. It is shown that the WCM is coupled to the geodesic acoustic mode (GAM)
 \, which explains the width of the WCM. Stability analysis shows that the 
 I-mode edge is peeling-ballooning stable and thus does not exhibit type-I 
 ELMs. The confinement improvement in I-mode is accompanied by a deepening 
 of the edge radial electric field well\, suggesting a reduction of turbule
 nce amplitudes due to E×B shear flow. Moreover\, while low-amplitude dens
 ity fluctuations are reduced in I-mode\, strongly intermittent high-amplit
 ude density bursts are observed by Doppler reflectometry at various turbul
 ence wavenumbers in the plasma edge inside the separatrix. They have a sol
 itary structure and are connected to the WCM. After their generation\, the
 y are expelled from the plasma and cause energy input into the divertor.\n
 \n 
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STATUS:CONFIRMED
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