In the quest to harness the power of the sun here on Earth, scientists are continually pushing the boundaries of fusion technology. A recent study published by Thomas Wilson of the UK Atomic Energy Authority (UKAEA) at Culham Campus, has shed new light on the challenges and opportunities facing the UK’s ambitious Spherical Tokamak for Energy Production (STEP) program. The research, focused on heating and current drive in spherical tokamaks, has significant implications for the future of fusion power and the energy sector at large.
At the heart of the STEP program is the goal of demonstrating net electrical output from a spherical tokamak, a compact and efficient design for fusion reactors. To achieve this, the plasma within the tokamak must be carefully controlled, with a significant portion of the current self-generated by the plasma pressure gradient. The remaining current is to be provided by a heating and current drive (HCD) system, a critical component in maintaining the plasma’s stability and performance.
Neutral beam injection (NBI) has long been a staple in fusion research, using high-energy beams of neutral particles to heat and drive current in the plasma. However, Wilson’s research suggests that while NBI has excellent current drive efficiency, it may not be the best fit for the STEP program. “In isolation, NBI has excellent current drive efficiency,” Wilson explains, “but once considered in an integrated design, the poor wall-plug efficiency, large size, and consequent high cost make NBI undesirable in STEP compared to microwave-based HCD.”
The study highlights several key challenges with using NBI in the STEP program. Firstly, the wall-plug efficiency—the ratio of output power to input power—is relatively low for NBI systems. This means that a significant amount of energy is lost in the process, making it less attractive for a commercial power plant. Additionally, the size and cost of NBI systems are substantial, posing further integration challenges.
Instead, Wilson’s research points to microwave-based HCD systems as a more viable option. These systems use radiofrequency waves to heat and drive current in the plasma, offering better wall-plug efficiency and a more compact design. This shift could have significant implications for the commercialization of fusion power, making it more economically competitive with traditional energy sources.
The findings of Wilson’s research, published in the journal Nuclear Fusion, which translates to Nuclear Fusion in English, are likely to influence the design and development of future fusion power plants. As the energy sector continues to seek clean, sustainable, and economically viable power sources, the insights gained from the STEP program and studies like Wilson’s will be invaluable. The journey to commercial fusion power is fraught with challenges, but with each step forward, the dream of harnessing the power of the stars becomes a little more tangible. The energy sector watches with bated breath as these developments unfold, hoping that the next breakthrough is just around the corner.