Driver options and burn-cycle selection based on power-reactor considerations Page: 3 of 25
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1. Motivation for this study - the STARFIRE reactor
The design team which created the STARFIRE reactor concept  was
strongly influenced by engineering experience and electric utility concerns to
select purely continuous (CW) tokamak operation as the preferred mode of
operation. This choice was based on intuitive feelings that CW operation
would result in a more desirable power reactor compared to one operating in
the conventional, ohmically heated (OH) and inductively driven mode. Certain
advantages of CW operation were incorporated into the design: (i) by eliminat-
ing the Ohmic heating coil (OHC) the central hole in the doughnut was mini-
mized, permitting a relatively compact (seven-meter major radius, R0) design;
(ii) the elimination of thermal fatigue in the first wall and limiter per-
mitted a design at higher thermal wall loads and created the opportunity to
utilize a solid breeder compound in the blanket; (iii) the expense of thermal
storage associated with cyclic operation was eliminated; (iv) the antitorque
structure for the toroidal field coils (TFC) was simplified by eliminating
fatigue as a consideration; (v) power supply costs were reduced through the
use of very long startup times (20 min) for the current and fusion power
ramps; (vi) electric energy storage was eliminated; and (vii) disruptions were
assumed to occur less frequently, resulting in less cumulative damage to the
first wall and limiter. These features, combined with a perceived higher
reliability of a complicated system when operating in a continuous mode,
permitted the design of an economically attractive reactor which could
approach the high availability goals (75-80%) required for power generation.
The penalty associated with C1 operation is due to the circulating power
and capital cost of the noninductive driver, and major compromises were made
ir the STARFIRE design in order to reduce the driver power to a tolera'le
level . The first major sacrifice was the selection of a rather low plasma
density (average electron density ne = 1.2 x 1020 m-3) since this is expected
to reduce noninductive current drive power. The drawback was that the fusion
power was considerably lower (with Te - 17 keV, Ti - 24 keV) for a fixed beta
limit (Bt - 0.067) and maximum toroidal magnetic field (BM - 11.1 T at the
TFC) than it would have been at the optimum density and temperatures (Re M Hi
2.4 x 1020 m-3 and T . Ti - 10 keV). The second major effort was the
search for desirable plasma equilibria which exhibit acceptably high stable
beta but minimize the total driver power required to sustain the toroidal cur-
rent, I0. The latter criterion demands a low current equilibrium with the
current density, j, peaked in the region of low electron density, ne, where
noninductive current drive is most efficient. These goals were met with a
hollow current density profile with I0 - 10.1 MA. The disadvantage here was
that this equilibrium was found to be stable to only modest values of beta.
As a result of these compromises the STARFIRE design appeared to offer a
desirable tradeoff between a circulating power and fusion power. It was esti-
mated that CW operation of STARFIRE resulted in a 20% net reduction ir. the
cost of energy compared to that of a comparable power reactor operating in a
conventional OH burn cycle. It is difficult to identify other tokamak design
improvements which can have such a-large influence on the cost of energy!
Nevertheless, we are motivated to question whether the situation might be
improved by a more judicious choice of current driver than the lower hybrid
waves which were selected as the reference driver for STARFIRE. In particular
we note that the 10-MA current required driver power absor eI in the plasma at
the level Pd - 67 MW, with circulating electric power of P e - 153 MW and
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Ehst, D.A. Driver options and burn-cycle selection based on power-reactor considerations, article, April 1, 1983; Illinois. (digital.library.unt.edu/ark:/67531/metadc1109058/m1/3/: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.