The advanced tokamak path to a compact net electric fusion pilot plant

Abstract

Physics-based simulations project a compact net electric fusion pilot plant with a nuclear testing mission is possible at modest scale based on the advanced tokamak concept, and identify key parameters for its optimization. These utilize a new integrated 1.5D core-edge approach for whole device modeling to predict performance by self-consistently applying transport, pedestal and current drive models to converge fully non-inductive stationary solutions, predicting profiles and energy confinement for a given density. This physics-based approach leads to new insights and understanding of reactor optimization. In particular, the levering role of high plasma density is identified, which raises fusion performance and self-driven ‘bootstrap currents’, to reduce current drive demands and enable high pressure with net electricity at a compact scale. Solutions at 6–7 T, ∼4 m radius and 200 MW net electricity are identified with margins and trade-offs possible between parameters. Current drive comes from neutral beam and ultra-high harmonic (helicon) fast wave, though other advanced approaches are not ruled out. The resulting low recirculating power in a double null configuration leads to a divertor heat flux challenge that is comparable to ITER, though reactor solutions may require more dissipation. Strong H-mode access (x2 margin over L–H transition scalings) and ITER-like heat fluxes are maintained with ∼20%–60% core radiation, though effects on confinement need further analysis. Neutron wall loadings appear tolerable. The approach would benefit from high temperature superconductors, as higher fields would increase performance margins while potential for demountability may facilitate nuclear testing. However, solutions are possible with conventional superconductors. An advanced load sharing and reactive bucking approach in the device centerpost region provides improved mechanical stress handling. The prospect of an affordable test device which could close the loop on net-electric production and conduct essential nuclear materials and breeding research is compelling, motivating research to validate the techniques and models employed here.

Radiative pulsed L-mode operation in ARC-class reactors

“…Higher f rad , is almost always desirable as it reduces the peak heat loads on the divertor. EU-DEMO, for example, is expected to require core radiation fractions > 60% [22] and proposed compact reactors are also expected to have radiation fractions of ∼ 40 − 60% [21,6]. While current experiments obtain high f rad with intrinsic low-Z or medium-Z impurities [23], intentional puffing or pellet injection of highly efficient radiators, such as Kr and Xe, using feedback control will be necessary to obtain large f rad without excessive dilution [24].…”

“…Enhanced confinement and internal transport barriers create large pressure gradients providing significant bootstrap current fractions, f bs . High confinement time then, allows minimization of plasma current improving stability while also reducing the external current drive requirements needed to obtain a steady-state reactor [5,4,6].…”

“…Since fusion power density scales like P fus ∼ β 2 B 4 [9], this technological advancement provides opportunities to develop or improve self-consistent reactor scenarios [10]. AT scenarios, combined with the stronger on-axis magnetic fields available using HTS have been shown to significantly decrease the minimum device major radius needed in a steady state reactor [11,4,6]. As size is one of the largest drivers increasing levelized cost of electricity, high B scenarios are economically attractive [4,12,13].…”

“…Figure 1. A fusion power density (fusion power P f us over the reactor volume V , or P f us /V ) comparison between the RPL mode ARC concept analyzed in this work and a number of other proposed tokamak reactor designs [5,14,15,4,6].…”

Validation and results of an approximate model for the stress of a Tokamak toroidal field coil at the inboard midplane

“…There are many systems codes in the literature, such as Culham Centre For Fusion Energy (CCFE) PROCESS, 18,19 Tokamak Energy's TESC, 15,20 General Atomics's GASC, 21,22 and ORNL's Unnamed FESS Systems code. 23,24 For a very tutorial approach, see papers from J. Freidberg's group.…”