Liquid metal condensation in the cavity of the HIBALL heavy ion fusion reactor

In the HIBALL heavy ion beam fusion reactor design, the INPORT concept is used to protect the first surface of the reactor from damage by the high energy X-rays, ion debris and fast neutrons from the exploding target. Liquid Li₁₇Pb₈₃ flows through porous SiC tubes and wets outside of the tubes with a layer of Li₁₇Pb₈₃. This Li₁₇Pb₈₃ film is evaporated on each shot by the target X-rays and ion debris. The mechanisms that control the vapor pressure of the chamber are: gas radiation, Li₁₇Pb₈₃ evaporation from the INPORT tubes, and gas condensation back onto the INPORT tubes. From the beam stripping cross section for Bi²⁺ ions on Pb the gas pressure (evaluated at 0°C) inside the chamber must be at or below 10⁻⁴ torr in order for the ion beam to reach the target and ignite it. The repetition rate is therefore determined by the time required to reestablish this pressure after a shot. Calculations are presented that indicate that this time is short enough to allow a 5 Hz repetition rate for a wide range of parameters.