ITER plans half-mile boron gas pipelines to purify fusion plasma

The ITER fusion project is developing an extensive boronization system to purify plasma and reduce impurities in its tokamak reactor, following a 2023 decision to switch plasma chamber armor from beryllium to tungsten. This system applies a thin boron layer (10-100 nanometers) to all plasma-facing surfaces, which captures oxygen impurities that could otherwise increase radiative losses and destabilize the plasma, especially during discharge initiation. The boron layer is deposited using diborane gas (a hydrogen-boron compound) injected into the tokamak, where it decomposes and chemically bonds to surfaces via a glow-discharge-assisted plasma process. The gas injection system involves over a kilometer of piping and 21 injection points within the facility. Designing this system at ITER’s unprecedented scale and in a tritiated environment posed challenges, including ensuring the compatibility of high-energy anodes with frequent boronization cycles and achieving even boron coverage. These issues were addressed through international collaboration and testing with other