Avalanches of explosions of helium-filled tungsten nanowires in plasma–surface interactions

Helium-filled tungsten nanostructure (fuzz) can arise in plasma–surface interactions in fusion devices and may exhibit spontaneous explosive breakdowns by electron emission current. We have obtained an estimation of the conductivity of such a nanostructure (W fuzz) in Tsventoukh and Kulagin [Phys. Plasmas31, 092509 (2024)] and found that it is a few orders of magnitude lower than that of solid tungsten. Here, we examine the corresponding Joule energy release leading to the explosive plasma formation. Lower-bound estimation of current density for both the nanowire ensemble (of micrometer scale) and for a single nanowire was about 1–10 MA/cm2. It defines the prevailing of Joule overheating over the thermal conduction cooling. The overheating time of the micrometer-scale fuzz region by this current density is about hundreds of nanoseconds. Helium-filled single nanowire overheating time should be less than tens of picoseconds—faster than bubble bursting time and annealing of nanowires. The corresponding current density is about 1 GA/cm2, it provides energy release of about 100 TW/cm3. Fast (tens of picoseconds) explosion of nanowire results in massive release of helium. Its flux onto the neighboring nanowire can provide fast transfer of energy (comparable with 100 TW/cm3) contributing to its explosion. Therefore, the exploding nanowires may “interact” via large fluxes of He massively released from them, providing avalanche-like multiplication of explosions.