Abstract: A first wall structure for a plasma chamber (200). The first wall structure comprises and inner wall (201) and a solid deposit (202). The inner wall is formed from a refractory metal or an alloy or composite thereof and has a plurality of pores. The solid deposit in thermal contact with the inner wall, such that the plurality of pores provide a passage from an exterior of the first wall structure to the deposit. The deposit consists of a material having a boiling point less than a melting point of the refractory metal. The first wall structure is configured such that at a normal operating temperature of the first wall structure, the deposit is solid.