59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017;
Milwaukee, Wisconsin
Session VI2: Transport
3:00 PM–5:00 PM,
Thursday, October 26, 2017
Room: 102ABC
Chair: Orso Meneghini, General Atomics
Abstract ID: BAPS.2017.DPP.VI2.4
Abstract: VI2.00004 : Lower Hybrid Wave Electric Field Vector Measurements Using Non-Perturbative Dynamic Stark Effect Optical Spectroscopy on Alcator C-Mod*
4:30 PM–5:00 PM
Preview Abstract
Abstract
Author:
E.H. Martin
(ORNL)
Plasma-wave interactions near the lower hybrid (LH) wave launcher can have a
major impact on driven LH current, especially in the high-density regime. To
identify the relevant physics responsible for this interaction a correlated
effort of experimental measurements and simulations of the LH wave electric
field vector, \textbf{E}$_{\mathrm{LH}}$, were carried out on Alcator C-Mod
using the SELHF (Stark Effect Lower Hybrid Field) diagnostic and COMSOL
modeling. For a range of plasma parameters observations show that:
1) The polarization \textbf{E}$_{\mathrm{LH}}$ resides primarily in the
radial-poloidal plane and becomes increasingly poloidal for locations away
and to the top of the LH launcher.
2) Saturation of the radial component of \textbf{E}$_{\mathrm{LH}}$ is
observed at an LH power density of approximately 12 MW/m$^{\mathrm{2}}$.
3) Reflectometry phase fluctuations were found to be correlated with
\textbar \textbf{E}$_{\mathrm{LH}}$\textbar .
These results suggest that the LH resonance cone and power spectrum may be
substantially modified near the LH launcher in the high-density regime from
the expected radial polarization and square root scaling of the magnitude
with LH power. Simulation of the experimental data was carried out through
development of a synthetic diagnostic using a full wave cold plasma COMSOL
model. Density fluctuations and reflectometry measured density profiles were
incorporated. Without density fluctuations, the synthetic
\textbf{E}$_{\mathrm{LH}}$ signal is dominantly in the radial direction and
scales with the square root of LH power, as expected. Increasing density
fluctuations in the model can cause the magnitude of
\textbf{E}$_{\mathrm{LH}}$ to decrease substantially and greatly vary the
direction of \textbf{E}$_{\mathrm{LH}}$.
The observations and results outlined above will be presented in detail and
the applicability of density fluctuations as a mechanism behind the behavior
of \textbf{E}$_{\mathrm{LH}}$ will be discussed.
*Funded by the DOE OFES (DE-AC05-00OR22725 and DE-FC02-99ER54512).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2017.DPP.VI2.4