A steady-state L-mode tokamak fusion reactor : large scale and minimum scale

Abstract

We perform extensive analysis on the physics of L-mode tokamak fusion reactors to identify (1) a favorable parameter space for a large scale steady-state reactor and (2) an operating point for a minimum scale steady-state reactor. The identification of the large scale parameter space is part of the 2008 MIT Nuclear Systems Design Project, which also includes sustainability and economic optimizations to identify a plausible operating point for a large scale (a 14 m major radius) hydrogen production reactor dubbed HYPERION. Due to the potentially prohibitive capital cost (a $50 billion) and exorbitant thermal power (a 35 GWth) of HYPERION, we identify a conservative estimate for the minimum scale of a similar steady-state L-mode reactor of approximately 7.5 meters, half the size of HYPERION and only 20% larger than ITER. This minimum scale reactor would require an on-coil magnetic field of a 16 T and a blanket power density of ~ 5 MW/m 2 . It would produce 7 GWth of power with a power gain of 30, and it would operate far from all stability and confinement limits. To confirm the viability of this operating point, we perform various 1-D calculations. The crucial advantage of a steady-state (or fully non-inductive) reactor is that it is not limited by flux swing and can operate continuously, recharging its solenoid during operation. The crucial advantages of L-mode are that it avoids instabilities associated with edge localized modes (ELMs) and that it allows volumetric heating in the mantle due to the absence of a pedestal. Steady-state L-mode tokamak reactors could be the future of controlled fusion research and even play an important role in meeting the world's clean energy needs.