The leading plasma-facing material for fusion reactors, prized for its extreme melting point and low sputtering yield under plasma bombardment.
Tungsten (W, Z=74) is the baseline plasma-facing material for virtually every next-generation fusion device, from ITER's full-tungsten divertor to the DEMO concepts under design in Europe, Japan, and Korea. Its selection rests on a combination of thermo-physical properties unmatched by any other refractory metal in the fusion operating envelope.
The divertor is the exhaust system of a tokamak, where escaping plasma particles strike solid surfaces at heat fluxes of 10--20 MW/m2 in steady state and up to several GW/m2 during transient events such as edge-localized modes (ELMs). Tungsten's melting point of 3,422 °C -- the highest of any metal -- provides the thermal margin that carbon and beryllium cannot. Its thermal conductivity (~170 W/m·K at room temperature) efficiently channels deposited heat to actively cooled substrates.1
A critical advantage of tungsten over lighter alternatives is its exceptionally low physical sputtering yield under deuterium and tritium bombardment. Because the mass ratio between fuel ions and tungsten atoms is extreme, momentum transfer is inefficient and erosion rates remain below ~10−3 atoms per incident ion at typical edge energies.2 However, tungsten's high atomic number means that even trace concentrations in the core plasma (~10−5 fractional density) cause severe radiative power losses that can cool and destabilize the discharge. Impurity transport and prompt redeposition physics therefore play an outsized role in reactor-relevant design.
Under 14.1 MeV neutron irradiation from D-T reactions, tungsten accumulates displacement damage and transmutation products -- principally rhenium and osmium -- that progressively harden and embrittle the material. The ductile-to-brittle transition temperature (DBTT), already above room temperature in unirradiated polycrystalline tungsten (~200--400 °C depending on processing), can rise by several hundred degrees after a few displacements per atom (dpa). This embrittlement is the single largest materials-qualification challenge for tungsten PFCs in a power plant, where components must survive 5--10 dpa over a multi-year service life.3
Researchers are pursuing multiple strategies to overcome intrinsic brittleness: oxide-dispersion-strengthened (ODS) tungsten, tungsten fiber-reinforced composites (Wf/W) that mimic ceramic-matrix composite toughening mechanisms, and nanostructured or potassium-doped variants that pin grain boundaries against recrystallization. Self-passivating tungsten alloys containing chromium and titanium additions are also under development to mitigate the safety risk of accidental air ingress, which can oxidize tungsten into volatile WO3 and mobilize activated inventory.4
ITER's decision to install an all-tungsten divertor from first plasma (replacing the original staged approach with a carbon-fiber-composite phase) underscores the community's confidence in tungsten as the reference PFC material. Qualification of tungsten under reactor-relevant neutron fluences remains a priority for facilities such as IFMIF-DONES and its successor programs.