2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005;
Denver, Colorado
Session QI1: Wave and Particle Interactions
9:30 AM–12:30 PM,
Thursday, October 27, 2005
Adam's Mark Hotel
Room: Plaza Ballroom ABC
Chair: Tom Intrator, Los Alamos National Laboratory
Abstract ID: BAPS.2005.DPP.QI1.1
Abstract: QI1.00001 : Current Drive by Electron Bernstein Waves*
9:30 AM–10:00 AM
Preview Abstract
Abstract
Author:
Abhay K. Ram
(Plasma Science and Fusion Center, M.I.T.)
In many conventional tokamaks, waves in the electron cyclotron range
of frequencies (ECRF), the X mode or the O mode,
have been successfully used for generating plasma
current and for modifying the current profile.
In the same range of frequencies the electron Bernstein waves
(EBW) offer
an intriguing alternative for generating plasma currents.
EBWs are particularly suited for the high-$\beta$ plasmas encountered
in spherical tori (ST) like NSTX. Unlike the X and O modes,
EBWs have no density limits
and are strongly absorbed by electrons in
the Doppler-shifted vicinity of harmonics of the electron
cyclotron resonance.
We have been studying two different
means of driving plasma currents by EBWs -- the Ohkawa scheme [1]
and the
Fisch-Boozer scheme [2]. The two schemes together provide enough
flexibility to
generate supplemental current for steady state operation and for
modifying
the current profile. We discuss the basic physics of the two
schemes as applied
to high-$\beta$ operations in NSTX.
More detailed insight is obtained from
computations using the code DKE which solves the drift kinetic
equation
with Fokker-Planck collision operator and quasilinear RF
diffusion operator.
We find that EBWs
damp on the tail of the electron distribution function.
Consequently, the
EBW current drive efficiency is higher than for the X or O modes.
Additionally, the core plasma
is better suited for the Fisch-Boozer scheme while
the Ohkawa scheme works best on the outboard plasma side.
In NSTX, current can be driven in the core and in the outboard
plasma region
using a single source frequency
corresponding to the fundamental electron cyclotron resonance in
the center.
These studies extend to traditional ECRF current drive and could have
applications in conventional tokamaks including ITER.
[1] T.\ Ohkawa, General Atomic Technical Report GA-A13847 (1976);
and J.\ Decker, in {\it AIP Conf.\ Proc.\ 694}, New York (2003),
p.\ 447.
[2] N.\ J.\ Fisch and A.\ H.\ Boozer, {\it Phys.\ Rev.\ Lett.}
{\bf 45}, 720 (1980).
*Supported by DoE grants DE-FG02-91ER-54109 and DE-FG02-99ER-54521.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.DPP.QI1.1