49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007;
Orlando, Florida
Session JI1: Waves and Energetic Particles
2:00 PM–5:00 PM,
Tuesday, November 13, 2007
Rosen Centre Hotel
Room: Junior Ballroom
Chair: James Van Dam, University of Texas
Abstract ID: BAPS.2007.DPP.JI1.3
Abstract: JI1.00003 : Lower Hybrid Current Drive Experiments on Alcator C-Mod: Comparison with Theory and Simulation*
3:00 PM–3:30 PM
Preview Abstract
Abstract
Author:
Paul Bonoli
(MIT - Plasma Science and Fusion Center)
Recently, lower hybrid current drive (LHCD) experiments have been
carried
out on Alcator C-Mod using an RF system consisting of 12
klystrons at 4.6
GHz, feeding a 4 $\times $ 22 waveguide array. Up to 900 kW of LH
power has
been coupled in the range1.6 $\le $ n$_{//} \quad \le $ 4), where
n$_{// }$is
the parallel refractive index. Driven LH currents have been
inferred from
magnetic measurements by extrapolating to zero loop voltage,
yielding an
efficiency of n$_{20}$I$_{LH}$R/P$_{LH} \quad \approx $ 0.3 [1].
We have
simulated the LH current drive in these discharges using the
combined ray
tracing / 3D (r, v$_{\bot }$, v$_{//})$ Fokker Planck code GENRAY
-- CQL3D
[2] and found similar current drive efficiencies. Measurements of
nonthermal
x-ray emission and electron cyclotron emission (ECE) confirm the
presence of
a significant fast electron population that varies with waveguide
phasing
and plasma density. Studies are currently underway to investigate
the role
of fast electron diffusion and full-wave effects such as
diffractional
broadening in determining the spatial and velocity space
structure of the
nonthermal electrons. The 3D (r, v$_{\bot }$, v$_{//})$ electron
distribution function from CQL3D has been used in synthetic
diagnostic codes
to simulate the measured hard x-ray and ECE emissions. Fast electron
diffusion times have been inferred from x-ray data by employing a
radial
diffusion operator in CQL3D and determining the fast electron
diffusivities
that are required to reproduce the experimentally observed
profiles of hard
x-ray emission. Finally, we have been performing full-wave LH field
simulations using the massively parallel TORIC --LH solver [3] in
order to
assess spatial and spectral broadening of the incident wave front
that can
result from diffraction and wave focusing effects.
\newline
\newline
[1] R. Parker, Bull. Am. Phys. Soc. \textbf{51}, 20 (2006).
\newline
[2] R.W. Harvey and M. McCoy, ``The CQL3D Fokker Planck Code,''
\textit{Proc. IAEA Tech. Comm. Meeting on Simulation and Modeling
of Thermonuclear Plasmas}, Montreal,
Canada, 1992.
\newline
[3] J. C. Wright \textit{et al.}, Nucl. Fusion \textbf{45}, 1411
(2005).
*Work done in collaboration with the Alcator C-Mod Team and the SciDAC Center for Simulation of Wave-Plasma Interactions. Work Supported by the US Department of Energy.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.DPP.JI1.3