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VERSION:2.0
PRODID:-//Memento EPFL//
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SUMMARY:Characterization of the core poloidal flow at ASDEX Upgrade
DTSTART:20180326T103000
DTSTAMP:20260916T034311Z
UID:995341026060e7e2e1e1786708a3f40c6307fb067d59dfc5b987cc56
CATEGORIES:Conferences - Seminars
DESCRIPTION:Alexander Lebschy\, IPP-Garching\, D\nIn tokamaks\, the toroid
 al rotation (utor) is essentially a free parameter that is usually dominat
 ed by the external momentum input from the neutral beam sources used to he
 at the plasma. The poloidal rotation (upol)\, on the other hand\, is stron
 gly damped due to the motion of the particles from the regions with higher
  magnetic field to lower magnetic field (and vice versa) and the associate
 d transfer from poloidal to toroidal rotation (magnetic pumping effect). D
 espite many previous investigations\, the nature of the core upol remains 
 an open question: studies at the DIII-D tokamak show that at low collision
 alities\, upol is significantly more in the ion diamagnetic direction than
  predicted from neoclassical theory. At higher collisionalities\, however\
 , a good agreement between experiment and theory was found at the TCV and 
 DIII-D tokamaks\, which is qualitatively consistent with the edge results 
 from both ALCATOR-C and ASDEX Upgrade (AUG).\nIn order to study the core i
 mpurity upol at AUG the core charge exchange recombination spectroscopy sy
 stems have been upgraded with new toroidal optical heads providing 70 addi
 tional lines-of-sight from the low-field side (LFS) to the high-field side
  (HFS) pedestal top. From theory it is known that any plasma flow can be e
 xpressed through a component parallel to the magnetic field and a rigid bo
 dy rotation such that the evaluation of the measurement of the core toroid
 al flow at two points of the same flux surface (LFS/HFS) enables an indire
 ct determination of the core upol with an accuracy better than 1 km=s for 
 certain plasma parameters and regimes.\nAt AUG\, the core upol at mid-radi
 us is found to be more ion diamagnetic directed than the neoclassical pred
 iction for both L- and H-mode discharges. At the plasma edge\, upol is fou
 nd to be electron diamagnetic directed and in good agreement with neoclass
 ical codes\, consistent with previous investigations at AUG. In order to c
 haracterize the core upol further at AUG\, different parameter dependencie
 s were investigated in the framework of the database. In the H-mode data t
 here is an increase in the difference between the experimentally measured 
 and theoretically predicted upol values at lower collisionalities concomit
 ant with larger normalized Larmor radii. A possible explanation for this r
 esult is a balance between the neoclassical damping and the turbulent driv
 e of upol. Within this picture\, the dominant driving mechanism for upol a
 t the lowest collisionalities of the database is turbulence. At higher col
 lisionalities\, the turbulent drive is reduced and the experimental profil
 es agree with the neoclassical predictions within their uncertainties.
LOCATION:ppb019
STATUS:CONFIRMED
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