Studies of liquid-metal erosion and free surface flowing liquid lithium retention of helium at the University of Illinois

The erosion of liquid-metals from low-energy particle bombardment at 45° incidence has been measured for a combination of species and target materials in the ion-surface interaction experiment (IIAX) at the University of Illinois Urbana-Champaign. Measurements include bombardment of liquid Li, Sn-Li and Sn by H⁺, D⁺, He⁺, and Li⁺ particles at energies from 100 to 1000 eV and temperatures from 20 to 420°C. Lithium sputtering near and just above the melting point shows little change compared to room temperature, solid-Li yields. When lithium is sputtered, about 2/3 of the sputtered flux is in the charged state. Temperature-dependent sputtering results show enhanced (up to an order-of-magnitude increase) sputter yields as the temperature of the sample is increased about a factor of two of the melting point for all liquid-metals studied (e.g., Li, Sn-Li, and Sn). The enhancement is explained by two mechanisms: near-surface binding of eroded atoms and the nature of the near-surface recoil energy and angular distribution as a function of temperature. The Flowing Liquid Retention Experiment (FLIRE) measured particle transport by flowing liquid films when exposed to energetic particles. Measurements of retention coefficient were performed for helium ions implanted by an ion beam into flowing liquid lithium at 230°C in the FLIRE facility. A linear dependence of the retention coefficient with implanted particle energy is found, given by the expression R = (5.3 ± 0.2) × 10^-3 keV^-1. The ion flux level did not have an effect for the flux level used in this work (∼10¹³ cm ^-2 s^-1) and square root dependence with velocity is also observed, which is in agreement with existing particle transport models.