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SUMMARY:Turbulence at the boundary of toroidal plasmas with open and close
 d magnetic flux surfaces
DTSTART:20150925T103000
DTEND:20150925T113000
DTSTAMP:20260916T050615Z
UID:5bd50d754d48f4592e0a54c1036b23c52dcb2011cc3b2ce5637ee9f7
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Fabio Avino\, CRPP-EPFL\nThe control and confinement of fu
 sion plasmas are currently limited by a lack of understanding of the physi
 cal mechanisms behind the evolution of the turbulent transport experienced
  by particles and energy. In-situ investigations of plasma turbulence is m
 ore accessible in basic plasma physics devices\, with the possibility of r
 igorously validating numerical codes. One of these experiments is TORPEX\,
  in which a comprehensive characterization of plasma turbulence has been c
 onducted in the presence of open helical magnetic field lines in toroidal 
 geometry. Closed magnetic flux surfaces can now be obtained by driving a c
 urrent inside the toroidal conductor recently installed on TORPEX\, which 
 generates the required poloidal magnetic field. This allows studying plasm
 a turbulence in magnetic geometries of increasing complexity. The simplest
  configuration of quasiconcentric flux surfaces is first explored\, with a
  detailed spectral characterization of the measured electrostatic quasi-co
 herent fluctuations. Measurements of the toroidal and poloidal mode number
 s reveal field-aligned modes. These present a poloidal localization indica
 ting a clear ballooning feature that is in agreement with the results of a
  linear fluid code. The first experimental measurements of plasma blobs in
  the presence of a single-null X-point are performed. Blobs radially propa
 gating outwards across the X-point are conditionally sampled\, which allow
 s us to track and analyze in detail the corresponding dynamics. The ExB dr
 ifts induced by the background potential gradients and the fluctuating pot
 ential dipole are both responsible for the measured blob acceleration in t
 he X-point region. The contribution of the potential dipole is explained o
 n the basis of an analytical model\, in which the variation of the magneti
 c field intensity close to the X-point plays a key role. This results in a
  blob speed scaling that is in good agreement with the measured values.
LOCATION:PPB 019
STATUS:CONFIRMED
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