  Practical extreme ultraviolet (EUV) sources yield the desired 13.5 nm
radiation but also generate debris, significantly limiting the lifespan of the
collector mirror in lithography. In this study, we explore the role of buffer
gas in transporting debris particles within a EUV source vessel using direct
numerical simulations (DNS). Our study involves a 2m $\times$ 1m $\times$ 1m
rectangular cavity with an injecting jet flow subjected to sideward outlet.
Debris particles are introduced into the cavity with specified initial
velocities, simulating a spherical radiating pattern with particle diameters
ranging from 0.1 $\mu$m to 1 $\mu$m. Varying the inflow velocity (from $1$m/s
to $50$m/s) of the buffer gas reveals a morphological transition in the flow
field. At low inflow velocities, the flow remains steady, whereas higher inflow
velocities induce the formation of clustered corner rolls. Upon reaching
sufficiently high inflow velocities, the jet flow can penetrate the entire
cavity, impacting the endwall. Interestingly, the resulting recirculation flow
leads to the spontaneous formation of spiraling outflow. The distinct flow
structures at various inflow velocities lead to distinct patterns of particle
transport. For low-speed gas, it is efficient in expelling all particles
smaller than 0.4 $\mu$m, while for high-speed gas, those fine particles
accumulate near the endwall and are challenging to be extracted. Our findings
highlight the significance of controlling flow conditions for effective debris
particle transport and clearance in diverse applications especially in EUV
source vessels.
