Physics Principles Behind a Compact Advanced Tokamak Power Plant*

Development of an efficient fusion reactor requires the simultaneous optimization of the plasma operating scenario and underlying hardware. These are inextricably linked; an effective operating scenario reduces demand on key components. The critical challenge is reduction of recirculating power. If significant auxiliary heating or current drive is needed, this drives up required fusion power, and thus size, heat flux, neutron load and cost of the device. The Advanced Tokamak concept addresses this through a fortuitous alignment of high beta operation with strong self-driven ‘bootstrap’ current and low turbulent transport. Here, strong research progress in transport, pedestal, stability and energetic particle physics has identified the key principles behind a solution. New integrated “full physics” simulations show the trade-offs and path to optimize the approach: high beta increases fusion performance, but increasing the density has greater leverage, raising bootstrap and decreasing current drive demands. With pedestal densities close to Greenwald density, solutions are indicated at ~4m radius and ~6T using conventional superconductors. However, higher field, high Tc superconductors provide greater margin in attainable beta, density, safety factor and neutron load, as well as easier maintenance and thus higher duty cycle. The plasma exhaust is managed by a combination of core radiation, flux expansion and radiative divertor, tuned to ensure an edge transport barrier is maintained. Divertor solutions similar to ITER are possible, but continuous operation may require a more advanced configuration to reduce erosion. Improved pedestal techniques, such as super-H mode are also highly levering. Research is needed to validate these concepts and establish the basis to proceed. This tutorial will explain the Advanced Tokamak approach and how it can accelerate the path to steady state fusion energy.