Options for heating, fueling, and current drive in MANTA, a high-field negative triangularity fusion pilot plant

Abstract

In this work, we assess how the performance of MANTA, a high-field, highly radiative, negative triangularity tokamak concept, depends on pellet fueling, ion cyclotron resonant frequency (ICRF) heating, and lower hybrid current drive (LHCD) schemes. Negative triangularity (NT) has been gaining momentum in the fusion community as a naturally, robustly ELM-free regime that is capable of power plant level performance. The MANTA device has been the subject of previous works regarding the whole-device design, power handling and divertor assessments, and core transport optimizations. Informed by these previous studies, we assess whether changes to the original MANTA heating and current drive scheme can positively affect performance, both in terms of lowering scrape-off layer power (improving power-handling, a primary benefit of NT) and maximizing plasma gain to levels necessary for an attractive fusion pilot plant. In this work, we find that the MANTA concept can yield improved performance in terms of plasma gain and scrape-off layer power by simultaneously going to lower input power and higher seeded impurity fraction. Also, we find that increasing the fueling magnitude can increase fusion power while minimally impacting scrape-off layer power. Performance can also be improved by optimizing the ICRF design; decreasing the minority ion fraction, decreasing the toroidal mode number of the injected wave, and switching from a helium-3 minority ion to a hydrogen-1 minority ion all result in increases to fusion power. The additional inboard space afforded by the NT geometry provides an opportunity for wave launch to be moved to the inboard side. This is beneficial for LHCD access and results in a wide range of potential current profiles in the edge, with the total driven current due to 25 MW of LHCD reaching up to 1.2 MA, or about 12% of the total current.