Closed-loop circulation for providing liquid metal to an interaction region at which an electron beam is to impact upon the liquid metal to produce X-rays is presented. In a method according to the invention, the pressure of the liquid metal is raised to at least 10 bar using a high-pressure pump (312). The pressurized liquid metal is then conducted to a nozzle (332) and ejected into a vacuum chamber (330) in the form of a spatially continuous jet. After passage through the vacuum chamber, the liquid metal is collected in a collection reservoir (334), and the pressure of the liquid metal is raised to an inlet pressure, e.g. using a primer pump (322), suitable for the inlet of the high-pressure pump. The invention also relates to a corresponding circulation system and an X-ray source provided with such circulation system.