#
54th Annual Meeting of the APS Division of Plasma Physics

## Volume 57, Number 12

##
Monday–Friday, October 29–November 2 2012;
Providence, Rhode Island

### Session GI2: Plasma Wall and Impurity Physics

9:30 AM–12:30 PM,
Tuesday, October 30, 2012

Room: Ballroom DE

Chair: John Canik, Oak Ridge National Laboratory

Abstract ID: BAPS.2012.DPP.GI2.6

### Abstract: GI2.00006 : Poloidal variation of high-Z impurity density in Alcator C-Mod ICRF-heated plasmas*

12:00 PM–12:30 PM

Preview Abstract
Abstract

####
Author:

Matthew Reinke

(MIT - Plasma Science and Fusion Center)

The poloidal variation of molybdenum density is measured in the core of
ICRF-heated Alcator C-Mod plasmas and found to exhibit strong in/out
asymmetries. Existing neoclassical parallel impurity transport theory is
extended to include the effects of fast-ions and is shown to agree
quantitatively with C-Mod measurements. The flux-surface variation of
molybdenum is well described by n$_{z}(\theta )$/$\langle $n$_{z}\rangle
$=1+n$_{z,c}$ cos($\theta )$+n$_{z,s}$sin($\theta )$, where -0.2 $<$
n$_{z,c}$/$\langle $n$_{z}\rangle \quad <$ 0.3 and -0.1 $<$
n$_{z,s}$/$\langle $n$_{z}\rangle \quad <$ 0.1 are observed over a wide range
of Ohmic, L/I-mode and EDA H-mode plasmas for r/a $<$ 0.9. The in/out
asymmetry, n$_{z,c}$/$\langle $n$_{z}\rangle $, is determined by a
combination of centrifugal force due to toroidal rotation, leading to
low-field side (LFS) accumulation, and poloidal electric fields sustained by
magnetic trapping of cyclotron heated minority ions, leading to high field
side (HFS) accumulation. While LFS accumulation due to centrifugal effects
has been seen on other tokamaks, this represents the first observation of
the effect driven entirely by intrinsic rotation. Scans of the D(H)
resonance layer are shown to modify the in/out asymmetry by altering the
fast-ion temperature anisotropy, T$_{-}$/T$_{\vert \vert }$, and changing
the ICRF power density, P$_{RF}$/n$_{e}$, either by ramping down the input
power or increasing the density is found to reduce HFS accumulation.
Observations of up/down asymmetries n$_{z,s}$/$\langle $n$_{z}\rangle $,
of molybdenum density are found to disagree with existing theories in the
trace limit, n$_{z}$Z$^{2}$/n$_{i} \quad \ll $ 1, in the collisionless main-ion
regime. The link between n$_{z}(\theta )$ and poloidal rotation,
v$_{\theta }$, is emphasized, as both are assumed to be determined by
neoclassical parallel impurity transport, and a more rigorous test of theory
which includes matching asymmetries and v$_{\theta }$ is discussed. The use
of the poloidal variation in n$_{z}$ as a diagnostic for E$_{\theta }$ and
T$_{-}$/T$_{\vert \vert }$ as well as the impact of n$_{z,c}$/$\langle
$n$_{z}\rangle $ on radial transport are also discussed.

*Supported by USDoE award DE-FC02-99ER54512 and an appointment to the US DOE Fusion Energy Postdoctoral Research Program administered by ORISE

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.DPP.GI2.6