Bernd David

Liquid metal anode X-ray sources and their potential applications

Abstract Conventional electron impact X-ray sources invariably use solid state anodes. In this article a novel type of X-ray source is described in which X-rays are produced in a turbulently flowing liquid metal separated from the vacuum region of the X-ray source by a thin foil. The three diffusion processes (electron diffusion, heat conduction and turbulent mixing) which, together with convection, are responsible for thermal transport in liquid anode sources are briefly discussed and their relative importance is quantitatively assessed. When the mean lengths of these three diffusion processes are combined into a single parameter, σ, a simple Gaussian model of the spatial dependence of the temperature profile can be used to predict the loadability (Wxa0m−2xa0K−1) of the LIMAX arrangement. This model suggests that a DC load of several tens of kW can be maintained on a focus of 1 mm2 effective area and this estimate is confirmed by results from an experimental LIMAX apparatus. As a natural extension of this work, the combination of a LIMAX source with a secondary fluorescence target is proposed to yield a high radiance source of quasimonochromatic radiation for X-ray scatter imaging applications. A brief discussion of this proposal is given in connection with its potential applications in the fields of industrial and medical X-ray scatter imaging.

DESIGN PARAMETERS FOR CRYOGENIC THERMOSYPHONS

Cryogenic thermosyphons are the thermal conductors of choice for a variety of applications such as conduction-cooled superconducting devices. They exhibit a small effective thermal resistance at small cross-sections. A careful design, however, is crucial to ensure sufficient heat transport for all possible heatloads. The aim of this work is to obtain experimental results on critical limitations and the effective thermal conductivity dependent on the length, the cross-sectional area, and the working liquid fill level of a thermosyphon for different heatloads. For the experiments, a modular thermosyphon was designed with 5 different adiabatic tubes of length [cm]/cross-sectional diameter [cm] 10/1, 10/2, 30/0.5, 30/1, 30/2, which can be mounted between condenser and evaporator. The thermosyphon was operated with different fill levels of either nitrogen or neon and different heatloads. The effective thermal conductivity between condenser and evaporator was determined, dependent on the design parameters menti...