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22-27 October 2018
Mahatma Mandir Conference Centre
Asia/Kolkata timezone
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Rotation-induced electrostatic-potentials and density asymmetries in NSTX

25 Oct 2018, 14:00
4h 45m
Mahatma Mandir Conference Centre

Mahatma Mandir Conference Centre

Gandhinagar (nearest Airport: Ahmedabad), India
Poster P6 Posters

Speaker

Dr Luis F. Delgado-Aparicio (Princeton Plasma Physics Laboratory)

Description

The computation of rotation-induced electrostatic potentials is currently being used to study the associated two-dimensional distribution of impurity density asymmetries in NSTX and NSTX-U plasmas. The main effect of toroidal rotation on heavy impurities is their radial displacement to the outer plasma, which result in a non-uniform distribution around a magnetic flux-surface. Due to the different effect of centrifugal forces on electrons, main ions and low- to high-Z impurity density, an electrostatic potential is generated to satisfy quasi-neutrality. This calculation relies on flux-surface quantities like electron and ion temperature $(T_{e,i})$ and rotation frequency $(\omega_{\phi})$ and finds the 2D electron, deuterium and carbon density profiles self-consistently assuming the presence of a poloidal variation due to centrifugal forces. The few assumptions considered include a zero electron mass, a deuterium plasma, a trace impurity with charge “Z” given by coronal equilibrium and equilibrated ion temperatures (e.g. $T_D=T_C=T_Z$). The iterative solution for the electrostatic potential from the measured carbon density and central toroidal rotation using NSTX data are routinely obtained and compared with the values derived using the ideal formalism which assumes that the main low-Z intrinsic impurity (e.g. Carbon) is in the trace limit $\alpha_{C}\equiv36n_{C}/n_{e}\ll1$; realistic values of the low-Z impurity strength factor can exceed one. While the carbon asymmetry is nearly three times stronger than the ideal description, the depth of the potential well in the high field side can reach -110 to -280 V for core rotation between 180 – 360 km/s. This computation is being used to increase our understanding of medium- and high-Z asymmetries and the reduction of Z-peaking, to examine the effect of electrostatic potentials possibly changing the heat and particle transport, the reduction of the underlying turbulence due to $E\times B$, radiation asymmetries before tearing mode onsets, as well as to aid the design of new diagnostics for NSTX-U (e.g. ME-SXR, XICS, Bolometers, etc). The presence of O, Ne, Ar, Fe, Mo and W are considered at the trace limit with very small changes to quasineutrality and $Z_{eff}$. This work is supported by the U.S. Department of Energy, Office of Fusion Energy Sciences under contract number DE-AC02-09CH11466.
Paper Number EX/P6-8
Country or International Organization United States of America

Primary author

Dr Luis F. Delgado-Aparicio (Princeton Plasma Physics Laboratory)

Co-authors

Dr Ahmed Diallo (PPPL) Dr B. LeBlanc (PPPL) Mr Gerrit J. Kramer (Princeton Plasma Physics Laboratory) Mr H. Yamazaki (University of Tokyo) Dr Mario Podesta (Princeton Plasma Physics Laboratory) Dr R. Bell (PPPL) Dr Stefan Gerhardt (Princeton Plasma Physics Laboratory) Prof. Yuichi Takase (University of Tokyo)

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Paper