Conceptual design and verification of long-distance laser-probe system for Li target diagnostics of intense fusion neutron source

Abstract We developed a diagnostics tool for a liquid lithium (Li) target intended for use in intense fusion neutron sources such as the International Fusion Materials Irradiation Facility (IFMIF). The current design of IFMIF requires that the thickness of the liquid-Li target be maintained to within ±1 mm while operating under normal conditions. This paper deals with two topics: a conceptual design of the Li target diagnostics and verification tests of a candidate diagnostics (long-distance LP system). The overall concept of the Li target diagnostics is described first, and then the system configuration of the long-distance LP method, which is to be installed 7 m in front the Li target to measure the Li target thickness accurately, is shown. In addition, we present the results of verification tests aiming to examine the applicability of the long-distance LP system. The precision error resulting from long-distance measurement was estimated using a stationary specular-reflection object and a water-model simulating the Li target. As a result, we verified that the LP system has a precision of 16–40 μm even at a sampling rate of 500 kHz measurement from a distance of 10 m.