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MetalJet X-Ray Tube Technology

The Concept

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.

Image of a conventional x-ray tube illustrating how the solid anode gets damaged by a high intensity electron beam focus.

 

Image of the metal jet x-ray source technology illustrating how the metal jet anode is insensitive to electron beam damage since the anode is continuously regenerated and already molten.

 

 

Power and brightness comparison of microfocus x-ray sources  

 

 

 

 

 

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.

 

Extreme Brightness

 

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.

 

 

 

 

X-ray spectra of liquid metal

 

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.

 

Gallium Alloy

 

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.

 

Indium Alloy

 

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.

  Typical x-ray spectra from metal-jet alloys containing indium (In) and gallium (Ga) compared to conventional solid anode spectra of copper (Cu) and silver (Ag)

 

 

   
Image of the shape of the x-ray spot from a metal jet x-ray source illustrating its very high quality with minimal energy in the wings of the spot.  

Spot Quality

 

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.

 

Tunable Size

 

Both the spot size and the aspect ratio can be tuned freely.

 

 

 

 

Source Stability

 

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.

 

Graph of the stability of the metal-jet x-ray spot over 24 hours illustrating how the standard deviation is better than 0.1 micron.