2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009;
Denver, Colorado
Session J15: Windows to Burning Plasmas
1:30 PM–3:18 PM,
Sunday, May 3, 2009
Room: Governor's Square 14
Sponsoring
Unit:
DPP
Chair: Vincent Chan, General Atomics
Abstract ID: BAPS.2009.APR.J15.1
Abstract: J15.00001 : Energetic Particle Diagnostics for Magnetic Fusion Experiments*
1:30 PM–2:06 PM
Preview Abstract
Abstract
Author:
William Heidbrink
(UC Irvine)
In magnetic confinement experiments,
energetic ions are produced
in fusion reactions,
through acceleration by RF waves, and by ionization of injected
neutral beams.
The distribution function $f$ that describes the energetic ion
population is
shaped by orbital effects, Coulomb collisions, atomic processes,
and interactions with waves, resulting in a distribution function
that has a
complicated dependence on velocity $\vec v$, spatial position
$\vec r$,
and time $t$. The diagnostic
challenge is to measure $f(\vec v,\vec r,t)$ in the harsh plasma
environment.
Many diagnostic
techniques rely on emission from fusion reactions or from
interaction with
a probe neutral beam; unconfined energetic particles are also
measured.
In all cases, the measurement effectively averages over the variables
that describe the distribution function. To understand these
complicated
averages, it is convenient to define an instrument function $W$
that describes
the diagnostic weighting in phase space; the measured signal is
then the
convolution of $W$ and $f$ over the phase space variables.
In practice, measured signals
from the various energetic-particle diagnostics often differ
dramatically but
qualitative differences are readily explained by differences in
instrument function $W$.
Owing to the complexity of $W$,
quantitative comparisons with a theoretically predicted $f$ require
forward modeling. A relatively new spectroscopic technique
dubbed fast-ion
D-alpha (FIDA) provides valuable data at the DIII-D tokamak
and the National Spherical Torus Experiment.
In plasmas with weak MHD activity,
FIDA measurements often compare
well with theoretical predictions. Simulations employing the
calculated
distribution function during RF heating also match many features
of the
FIDA measurements. On the other hand, flattened fast-ion profiles
observed
during strong energetic-particle-driven instabilities
are harder to explain theoretically.
*Supported by the DOE
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.APR.J15.1