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.JI1.5
Abstract: JI1.00005 : HHFW Heating Efficiency and Current Drive Enhancement at Longer Wavelengths on NSTX*
4:00 PM–4:30 PM
Preview Abstract
Abstract
Author:
Joel Hosea
(Princeton Plasma Physics Laboratory)
High harmonic fast wave (HHFW) heating and current drive (CD) are
being developed on NSTX for supporting startup and sustainment of
the ST plasma. Considerable enhancement of the core heating
efficiency ($\eta$) under CD conditions has been demonstrated,
correlating strongly with
locating the onset density for fast wave perpendicular
propagation --
n$_{onset }\propto {\rm B}_{\phi }\times $ k$_{\vert \vert
}^{2}$/$\omega $ -- away from the antenna/wall. FW fields
propagating
close to the wall with decreasing B$_{\phi }$ and k$_{\vert \vert
}$ could
enhance both parametric decay instability (PDI) losses and losses
in sheaths
and structures around the machine. HHFW RF power delivered to the
core
plasma of NSTX is strongly reduced as k$_{\vert \vert }$ is
reduced -- for
${\rm B}_{\Phi }$= 4.5kG, heating is $\sim $ 1/2 as
effective at k$_{\phi }$= - 7m$^{-1}$ as at 14 m$^{-1}$
and $\sim $
1/10 as effective at - 3m$^{-1}$. A dramatic increase in $\eta $
is observed
for k$_{\phi }$ - 7m$^{-1}$ when B$_{\phi }$ is increased
to 5.5 kG
(central T$_{e}$ near 4 keV at P$_{RF}$ = 2 MW), when the density
2 cm in
front of the antenna is at or below n$_{onset}$. However, $\eta $
is not
improved when the density immediately in front of the antenna is
elevated
relative to the onset value. Furthermore, $\eta $ at even lower
k$_{\phi }$
still falls off rapidly with the k$_{\phi }$value. Measured edge ion
heating, attributable to PDI, does not change significantly with
B$_{\phi }$
and thus the improvement in $\eta $is attributed to a
reduction of
surface FW losses. This work is important for understanding the
role of
perpendicular propagation of fast waves near the antenna/wall on
surface
power losses generally, and has important implications for FW
heating
efficiency in the standard minority regimes as well. For example,
the
antenna bombardment observed for k$_{\vert \vert }$ near zero
excitation on
TFTR can be attributed to n$_{onset}$ being exceeded at the
antenna face.
Improved detection of CD effects under conditions of higher coupling
efficiency on NSTX will be presented.
*Collaborators: The NSTX Team. This work was supported by US DOE Contract No. DE-AC02-76CH03073.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.DPP.JI1.5