56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014;
New Orleans, Louisiana
Session YI1: Fast Ions, Momentum Input, RF, and Current Drive
9:30 AM–12:30 PM,
Friday, October 31, 2014
Room: Acadia
Chair: Zhihong Lin, University of California, Irvine
Abstract ID: BAPS.2014.DPP.YI1.6
Abstract: YI1.00006 : Energy Channeling and Coupling of Neutral-beam-driven Compressional Alfv\'{e}n Eigenmodes to Kinetic Alfv\'{e}n Waves in NSTX*
12:00 PM–12:30 PM
Preview Abstract
Abstract
Author:
Elena Belova
(PPPL)
Experimental observations from the National Spherical Torus Experiment
(NSTX) have linked strong activity of global (GAEs) and compressional (CAEs)
Alfven eigenmodes with a flattening of the electron temperature profile in
beam heated plasmas in NSTX [1]. Previous theoretical studies attributed
this effect to an enhanced electron transport due to these modes [2]. This
work presents the first self-consistent simulations of neutral-beam-driven
CAEs demonstrating an important alternative, an efficient energy channeling
mechanism that will occur for any unstable CAE in NSTX or other toroidal
devices. Three-dimensional hybrid MHD-particle simulations using the HYM
code for an NSTX discharge (141398) show unstable CAEs for a range of
toroidal mode numbers, n$=$4-9, and frequencies below the ion cyclotron
frequency. It is found that an essential feature of CAE modes in NSTX is
their coupling to kinetic Alfven waves (KAW) that occurs on the high-field
side at the Alfven resonance location. The radial width of the KAW is found
to be comparable to the fast ion Larmor radius. The beam-driven CAE can
mode-convert to KAW, channeling energy from the beam ions at the injection
region near the magnetic axis to the location of the resonant mode
conversion at the edge of the beam density profile. This mechanism can
explain the reduced heating of the plasma core in NSTX. The NBI power
transferred to one CAE has been estimated as up to P$=$0.4MW, based on
measured displacement amplitudes and HYM calculated mode structure. The
energy flux from the CAE to the KAW and dissipation at the resonance
location can have a direct effect on the temperature profile with changes in
core electron temperature up to several hundred eV. It is shown that strong
CAE/KAW coupling follows from the dispersion relation, and will occur for
any unstable CAE in NSTX or other toroidal devices, independent of toroidal
mode number or mode frequency.
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[1] D. Stutman, et al., Phys. Rev. Lett. \textbf{102}, 115002 (2009).\\[0pt]
[2] N.N. Gorelenkov, D. Stutman, K. Tritz et al., Nucl. Fusion \textbf{50}
084012 (2010).
*Supported by US DOE contract \# DE-AC02-09CH11466.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.DPP.YI1.6