Assessment of torsatrons as reactors

Abstract

Stellarators have significant operational advantages over tokamaks as ignited steady-state reactors because stellarators have no dangerous disruptions and no need for continuous current &"ive or power recirculated to the plasma, both easing the first wall, blanket, and shield design; less severe constraints on the plasma parameters and profiles; and better access for maintenance. This study shows that a reactor based on the torsatron configuration (a stellarator variant) could also have up to double the mass utilization efficiency (MUE) and a significantly lower cost of electricity (COE) than a conventional tokamak reactor (ARIES-I) for a range of assumptions. Torsatron reactors can have much smaller coil systems than tokamak reactors because the coils are closer to the plasma and they have a smaller cross section (higher average current density because of the lower magnetic field). The reactor optimization approach and the costing and component models are those used in the current stage of the ARIES-I tokamak reactor study. Typical reactor parameters for a 1-GW(e) Compact Torsatron reactor example are major radius RO = 6.6-8.8 m, on-axis magnetic field B0 = 4.8-7.5 T, Bmax (on coils) = 16 T, MUE = 140-210 kW(e)/tonne, and COE (in constant 1990 dollars) = 67-79 mill/kW(e)h. The results are relatively sensitive to assumptions on the level of confinement improvement and the blanket thickness under the inboard half of the helical windings but relatively insensitive to other assumptions.

Evaluation of Torsatrons as reactors

“…The ARIES-I" case is ARIES-I recalculated with the improved blanket and shield models developed in the ARIES-IV studies. When ARIES-I was recalculated [ 16] with the stellarator reactor code to benchmark our calculations and to provide a more detailed comparison with the torsatron reactor calculations, the values obtained were very close (a few tenths of a percent) to the values obtained in a May 1992 recalculation of ARIES-1. The slight differences arose from the different approximations used in calculating the masses of the blankets and shields.…”

“…14. The optimum values (with respect to the minimum value for the COE) for (fl) and H" are related and are not necessarily the limiting values. For constant (7) and H', (_ 0, (H') 2.5 because of the p-0.6 dependence in XE [16]. Here (n) is constant with H" and (/3) ,,, (H') 2 because (T) (and the fraction of alphaparticle heating lost) changes with H'.…”

“…17; B0 only decreases by 13% over this range. For constant (7"), (fl) *, PE [16]. Here (fl) *, PE0.9 because (7) and H" change with PE.…”

“…The main plasma parameters obtained for the COE-optimized CT6 reference case are compared in Table 3 with those for ARIES-I', a first-stability tokamak reactor, and ARIES-IV, a second-stability tokamak reactor [15]. The CT6 reference case is an updated version of an earlier CT6 reactor [ 16] based on a 0-D transport model and a much thinner blanket '_,ndshield underthe inboard half of the helical windings. The ARIES-I" case is ARIES-I recalculated with the improved blanket and shield models developed in the ARIES-IV studies.…”