49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007;
Orlando, Florida
Session NI1: Electron Confinement and Zonal Flows
9:30 AM–12:30 PM,
Wednesday, November 14, 2007
Rosen Centre Hotel
Room: Junior Ballroom
Chair: Stanley Kaye, Princeton Plasma Physics Laboratory
Abstract ID: BAPS.2007.DPP.NI1.4
Abstract: NI1.00004 : A quantitative account of electron energy transport in an NSTX plasma*
11:00 AM–11:30 AM
Preview Abstract
Abstract
Author:
Dave Mikkelsen
(Princeton Plasma Physics Lab)
Anomalous electron transport in magnetized plasmas can be a major
obstacle
in the way toward practical nuclear fusion power, and it has been an
outstanding problem for almost half a century. Here we report the
first
successful quantitative accounting of the electron thermal
conductivity
$\chi _{e}$ in a tokamak experiment due to imperfect magnetic
surfaces$^{1}$ caused by the microtearing instabilities. The
unstable
spectrum is calculated with the GS2 code for a well-behaved
H-mode plasma in
NSTX (R/a=0.85m/0.67m) with 6 MW deuterium neutral beam heating at
I$_{p}$=0.75 MA, B$_{t}$=0.5 T. The application of existing
nonlinear
theory$^{2}$ showed that the unstable modes can produce overlapping
resistive layers and stochastic magnetic fields. The calculated
$\chi
_{e}$ based on the theory$^{1}$ is in good agreement with the
values from
transport analysis of the experimental data over the entire
region (0.4 $<$
r/a $<$ 0.75), where the electron temperature gradient is strong
enough to
make microtearing the most unstable mode. There is no adjustable
parameter
in this comparison. In a discharge with reversed central magnetic
shear and
an L-mode edge, microtearing modes are found to be stable. The
central
electron temperature is 50{\%} higher (2 keV vs 1.3 keV) than in the
comparison shot with the microtearing instability and the same
controlled
tokamak parameters like plasma current, density, magnetic field,
plasma
shape, position and neutral beam heating power. This is a strong
indication
that this instability may be the dominant mechanism responsible
for the
electron transport in this type of plasma. Since the microtearing
mode is
difficult to stabilize with velocity shear, this instability is
an important
limit$^{3}$ on the electron temperature in spherical tokamak
configurations
where the usual long wavelength instabilities are not present.
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*This work is carried out in collaboration with Drs. S. Kaye, D.
R. Mikkelsen, J. Krommes, K. Hill, R. Bell, and B. LeBlanc. It is
supported by USDoE contract No. DE-AC02-76CH03073.
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$^{1}$A. B. Rechester, M. N. Rosenbluth, Phys. Rev. Lett.
\underline {40}, 38 (1978).
\newline
$^{2}$J. F. Drake et al., Phys. Rev. Lett. \underline {44}, 994
(1980).
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$^{3}$M. Kotschenreuther, W. Dorland et al., Nucl. Fusion
\underline {40}, 677 (2000).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.DPP.NI1.4