Speaker
Takashi Maekawa
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1046.pdf
Non-inductive current start-up and ramp-up by X-wave ECCD
in fusion tokamaks
Takashi Maekawa, Masaki Uchida and Hitoshi Tanaka
Graduate School of Energy Science, Kyoto University, Kyoto, Japan
Some improvement in engineering of tokamak reactors would be possible, if a hot plasma
with Te up to a few keV and Ip up to a few hundred kilo amperes could be non-inductively
built up prior to inductive current ramp-up to a full current for fusion ignition and burning.
From the view point of reactor engineering, electron cyclotron (EC) heating and current drive
(ECH/ECCD) is attractive for the non-inductive build up.
In a startup discharge, toroidal plasma current is initially low and all the plasma would be
in open fields. As the current develops by ECH, a small closed flux surface would appear and
then the current inside the surface would develop by ECCD. Eventually the discharge would
develop into the tokamak stage, where whole the plasma is contained in large closed flux
surfaces, and the plasma is heated with the current ramp-up by ECCD, and finally the goal of
hot plasma buildup would be accomplished. It has been shown that oblique X-waves are
useful for ECH/ECCD for every stage of the discharge and it was suggested that an injection
power of Prf~4 MW could build up a hot plasma with the toroidal plasma current of
Ip~200kA, ne~1.2x1019m-3, Te~2keV, a=1 m and R0=5.1m in ITER [1].
As the electron temperature Te increases into keV range, however, plasma conductivity
becomes very high and the return current driven by the self-induction voltage from EC driven
current would hamper the current ramp-up. Here we study the current ramp-up for an ITER
case using a current circuit model for the ECCD driven current and the return current. The
circuit equation is coupled with the ECCD efficiency equation [2] and the ITERL-97P energy
confinement scaling [3]. Numerical study for various cases elucidates key points for efficient
current ramp-up in keV range plasmas.
[1] T. Maekawa, M. Uchida and H. Tanaka, Nucl. Fusion 58 (2018) 016037.
[2] C.F.F. Karney and N.J. Fisch, Phys. Fluids, 29 (1986)180.
[3] S.M. Kaye and ITER Confinement Database Working Group Nucl. Fusion 37(1997) 1303.
