Abstract
X-ray sources are used for both scientific instrumentation and inspection applications. In X-ray photoelectron spectroscopy (XPS), aluminum Kα X-rays are generated through electron beam irradiation of a copper-based X-ray anode incorporating a thin surface layer of aluminum. The maximum power operation of the X-ray anode is limited by the relatively low melting point of the aluminum. Hence, optimization of the materials and design of the X-ray anode to transfer heat away from the aluminum thin film is key to maximizing performance. Finite element analysis (FEA) has been employed to model the heat transfer of a water-cooled copper-based X-ray anode with and without the use of a chemical vapor deposited (CVD) diamond heat spreader. The modeling approach was to construct a representative baseline model, and then to vary different parameters systematically, solving for a steady-state thermal condition, and observing the effect on the maximum temperature attained. The model indicates that a CVD diamond heat spreader (with isotropic thermal properties) brazed into the copper body reduces the maximum temperature in the 4 μm aluminum layer from 613 °C to 301 °C. Introducing realistic anisotropy and inhomogeneity in the thermal conductivity (TC) of the CVD diamond has no significant effect on heat transfer if the aluminum film is on the CVD diamond growth face (with the highest TC). However, if the aluminum layer is on the CVD diamond nucleation face (with the lowest TC), the maximum temperature is 575 °C. Implications for anode design are discussed.
Highlights
X-rays are used as an excitation source in analytical techniques such as X-ray photoelectron spectroscopy (XPS) and X-ray diffraction, and in X-ray inspection and imaging
Some anodes employ a chemical vapor deposited (CVD) diamond heat spreader, brazed flush into the copper body beneath the aluminum film (Fig. 1). This technical brief reports the findings of finite element analysis (FEA) of the thermal performance of a watercooled anode both with and without a diamond heat spreader, and the effects of material and geometry variations
The thermal conductivity (TC) of both the diamond heat spreader and the aluminum anode material has a large effect on the aluminum temperature (Fig. 6)
Summary
X-rays are used as an excitation source in analytical techniques such as X-ray photoelectron spectroscopy (XPS) and X-ray diffraction, and in X-ray inspection and imaging. X-rays are produced by accelerating high-energy electrons to strike a metallic anode where the electrons cause the emission of X-ray photons through anode atomic core-level excitation This conversion is inefficient, with 99% of the electron energy converted into heat within the anode assembly. Some anodes employ a chemical vapor deposited (CVD) diamond heat spreader, brazed flush into the copper body beneath the aluminum film (Fig. 1). This technical brief reports the findings of finite element analysis (FEA) of the thermal performance of a watercooled anode both with and without a diamond heat spreader, and the effects of material and geometry variations
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