Commonwealth Fusion is advancing fusion energy with its ARC reactor, designed to deliver 400 MW of electricity to the grid. Unlike ITER, which targets the 2030s for initial plasma operations, ARC aims for near-term deployment using high-temperature superconductors to create powerful magnetic fields. This allows a smaller reactor footprint while scaling fusion power. The design hinges on deuterium-tritium fusion, producing helium 'ash', neutrons, and radiation. Neutrons heat molten salt for electricity generation, while lithium in the salt breeds more tritium fuel. ARC's 400 MW output represents a compromise: 1.13 GW total fusion power, with 500 MW thermal output, after accounting for operational needs and inefficiencies. Power is generated in 15-minute fusion bursts separated by one-minute resets to manage heat retention.

The core technical challenge lies in managing magnetic instabilities and helium ash accumulation. Plasma instabilities risk damaging components; Commonwealth plans to quench the system quickly during events. Helium ash, which can disrupt reactions, is addressed via a divertor system expelling impurities like argon. Models predict sufficient pressure to remove ash, but empirical testing with SPARC is crucial. The reactor's modular design allows component replacement every one to two years, including tungsten-lined walls to withstand radiation and plasma erosion. This adaptability lets engineers refine the design post-construction. SPARC, currently 70% built, will provide essential data on runaway electrons and instability management before ARC operates.

ARC's success could redefine fusion timelines. By leveraging high-temperature superconductors, Commonwealth Fusion targets faster deployment than traditional paths reliant on ITER. This approach addresses a key industry bottleneck: scaling from experimental reactors to power plants. However, uncertainties remain. Predicted power outputs vary from 900 MW to 1.3 GW, affecting the 400 MW grid output estimate. Effectively handling instabilities and ash without excessive component wear is unproven. While SPARC's data will reduce risks, demonstrating reliable, commercial-scale fusion power remains a significant engineering hurdle. The path shows technical promise but requires successful execution of complex physics at scale.