An overview of the mesh used as the basis of the analysis. Colour variations within components (e.g., within aluminum) are visual aids to facilitate the modeling process.
Torr Scientific has been manufacturing and refurbishing X-ray anodes for 22 years. We can manufacture from scratch from the customer’s drawing, or we can refurbish or repair to restore an anode to its original condition, if not better. Our engineers can design an X-ray anode to a customer’s requirements. We have finite element analysis capability to optimize thermal performance and structural design, and we have electron optics simulation capability to optimize the electron beam. Monte Carlo analysis of electron penetration is used to optimize the thickness of the anode coating.
The copper-bodied model (right) has a maximum steady-state temperature 613℃, whereas the baseline model with the diamond heat spreader (left, same temperature scale) has maximum 301℃
X-ray anodes work by receiving a beam of accelerated electrons in vacuum. As the electrons are brought to a stop, some of their energy is converted into X-ray radiation whose spectrum depends on the anode material and the energy of the electrons. An X-ray anode might be encapsulated in an evacuated tube for use in inspection or high energy analytical applications. Alternatively, an X-ray anode on a vacuum flange might be used as a source of lower energy radiation for surface analysis techniques such as X-ray photoelectron spectrometry (XPS). The X-rays are generated in the anode material, usually a thin film coated onto a copper heat sink. The anode material may be chosen for its characteristic X-ray peaks, but must also be robust enough to survive the electron bombardment. Materials used for anodes include W, Al, Y, Zr, Mg, Si, Ag, Ti and Cr. Less than 1% of the electron energy is converted to X-ray radiation, the rest is deposited as heat and must be managed. Power densities where the beam hits the anode are routinely many orders of magnitude greater than the critical heat flux value that a typical water-cooled nuclear reactor must never be allowed to reach. Many X-ray anodes are water cooled.
Advances in materials science have enabled another technique for optimal heat management in X-ray anodes. Diamond has the highest thermal conductivity of any known material, and in good quality material can be 5x that of copper. Chemical vapour deposition (CVD) techniques have led to affordable, high‑quality diamond material suitable for heat spreading applications. Experimentsa and modelsb in the scientific literature show that a doubling of power density is possible when a diamond heat spreader is deployed beneath the anode film. Torr Scientific can braze a CVD diamond heat spreader into the anode body, activate and prime the diamond surface and apply a well‑adhered anode film. The thermal properties of CVD diamond may be extreme, but they can be complex, varying with direction and position. Torr Scientific have gained a good understanding of this complexity through in-depth modellingb, allowing the very best performance to be exploited through proper orientation of the diamond.
a Li, X.; Wang, X.; Li, Y.; Liu, Y (2020). Production and Heat Properties of an X-ray Reflective Anode Based on a Diamond Heat Buffer Layer. Materials 2020 (13), 241. Open access
b Stupple, D.; Kemp, V.; Oldfield, M.; Watts, Prof. J.; Baker, Dr. M. (2018). Modeling of Heat Transfer in an Aluminum X-ray Anode Employing a CVD Diamond Heat Spreader. Journal of Heat Transfer 140 (12), 124501. Open access
