This study investigated the inflow angle and capture coefficient є using numerical simulation, and then validated the inferred relation by experimentation. The inflow angular dependent capture coefficient є(θ) of a cylindrical cryopump used to create a high-vacuum environment for electric propulsion tests was calculated from a three-dimensional particle trajectory simulation. Results show that є(θ) is 0.25–0.83 as a function of the inflow angle of particles to the pump surface. A total capture coefficient єtotal is obtained by integration of the є(θ) multiplied by the flux distribution of particle to the pump surface. For the thermal inflow flux, єtotal is calculated as 0.55 for the cylindrical cryopump alone and 0.70 for a cylindrical cryopump with a duct for a gate valve. The analytically estimated єtotal was evaluated by pressure distribution measurements taken in a φ2.0 × 3.0 m vacuum chamber evacuated by two cylindrical cryopumps. The numerically simulated pressure shows good agreement with the measured pressure within ±6%. Further investigation of the improvement of the єtotal when the particles flow directly to a pump demonstrates that єtotal increases 16% when particles flow directly to a pump.
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