Dynamic Deuterium Retention in Tungsten After Plasma Exposures in DIONISOS*

The dependence of dynamic deuterium (D) retention on particle fluence and surface temperature in hot-rolled polished polycrystalline tungsten (W) is studied under steady-state D plasma exposure in the DIONISOS linear RF helicon-plasma device using Nuclear Reaction Analysis (NRA) with a $^3$He ion beam.

A commercial tokamak will operate in short or long plasma pulses, requiring the vacuum vessel to be pumped down between pulses. The outgassing of dynamically retained fuel from the walls significantly affects the time needed to pump down to the required base pressure and start a new pulse, thus limiting the reactor's operating time. Additionally, the loss of fusion fuel, especially tritium (T), to the walls is undesirable, presenting further challenges in achieving tritium fuel self-sufficiency. A major obstacle in studying dynamic retention is the rapid release of fuel from the material after plasma termination, making it undetectable ex-situ.

Two sets of steady-state D plasma exposures with constant flux ($\sim10^{21}  m^{-2} s^{-1}$) will be conducted on DIONISOS. The first set will focus on temperature dependence ($\sim RT$, $300^{\circ}C$, and $750^{\circ}C$), while the second set will investigate fluence dependence ($\sim 10^{24}$, $10^{25}$, and $10^{26}$ $m^{-2}$). The study aims to deduce the relationship between D dynamic outgassing and both particle fluence and surface temperature, while maintaining constant particle impact energy.