Plasma characterization of tin-enriched clouds generated during the exposure of a liquid tin Capillary Porous System target at the OLMAT High Heat Flux facility

In future magnetic fusion devices, where extended pulse operation will be required, Liquid Metal (LM) Plasma Facing Components (PFCs), in particular tin, have been proposed as alternative to tungsten (W) ones.  This is done in an attempt to overcome the limitations of W in terms of PFC lifetime and resilience to transient events. An advantage of LMs rely on the possibility of harnessing vapor shielding effects to dissipate part of the power exhaust while also offering natural protection to the underlying armor against disruptions [1].  The OLMAT (Optimization of Liquid Metal Advanced Targets) High Heat Flux (HHF) facility [2] is used to pursue the experimental development of LM PFCs by enabling the exposition to heat fluxes up to 58 MW/m² in pulsed operation (30-150 ms duration, frequency up to 2 pulses/min). The results obtained with a W felt target filled with liquid tin and embedded single Langmuir Probe (LP) are presented. This allowed diagnosing the plasma cloud (Te and n_e) created in front of the target during the exposure at temporal scales where tin vaporization contributed to induce shielding effects on the incoming heat fluxes. Challenges regarding the LP interpretation due to possible thermionic electron emission and by the presence of tin content in the plasma are discussed. The results are complemented with line spectroscopy, fast-frame/infrared camera and pyrometry measures attempting the pioneering, in-situ diagnosis of tin-enriched plasmas of primary interest for alternative LM divertor scenarios