The MetalJet X-ray tube is a conventional microfocus tube with the solid-metal anode replaced by a liquid-metal jet. This type of anode is continuously regenerated and already in the molten stage. Thereby, the classical power limit of an X-ray source, when the anode is permanently damaged by the electron beam, may be disregarded. Especially in the microfocus X-ray spot size range, from about 5 µm diameter to a few tens of µm, a source based on a liquid-metal-jet anode significantly outperform a classical solid anode X-ray source.
The MetalJet X-ray tubes are conventional microfocus tubes with the solid-metal anode replaced by a liquid-metal jet. The metal jet supports higher electron-beam power and can therefore generate higher X-ray flux.
Liquid MetalJet anode.
Power Loading Capability
The X-ray power of all electron-impact X-ray generators is limited by the thermal power loading of the anode. In conventional solid anode technology, the surface temperature of the anode must be well below the melting point in order to avoid damage and this is fundamentally limited by the anode target material properties, primarily the melting point, the vapor pressure and especially the thermal conductivity. The liquid-metal anode is different since the limitation to maintain the target at well below melting point in removed. This is due to the fact that the material is already molten and that it is regenerative by nature, supplying new fresh target material at a rate of close to 100 m/s. This means that the electron beam and anode interaction may be destructive.
Somewhat counter-intuitively, the power loading capability of small-focus X-ray tubes roughly scale with the diameter and not the area of the e-beam focus. Therefore, the brightness is inversely proportional to the source diameter.By combining extreme power loading capability and a small electron focus, a liquid-jet-source can achieve unprecedented brightness at micron spot sizes.
In order to reach different X-ray emission lines, different metal alloys are used. First generation metal-jet sources feature metal alloys that are molten at more or less room temperature. Still, several alloys have emission characteristics similar to regular solid anodes. Future upgrades can also include alloys with higher melting points.
A gallium (Ga) rich alloy has Kα emission of 9.2 keV which is close to the copper (Cu) Kα emission line at 8.0 keV.
An indium (In) rich alloy has Kα emission of 24.2 keV which is close to the silver (Ag) Kα emission line at 22.1 keV.
Thanks to advanced electromagnetic focusing and correctional optics together with a high brightness LaB6 cathode, a high quality e-beam focus is achieved. Together with a continuously generated smooth liquid target surface, the source produces X-ray spots of very high quality.
Both the spot size and the aspect ratio can be tuned freely.
The spatial stability of the source is very high. The image to the right illustrates a spot centroid standard deviation of < 0.1 µm over 24 hours, as taken with pinhole camera mechanically coupled to the source.
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