- X-ray Tubes
- Multilayer Optics
- Microfocus Source IµS
ixtubes – Microfocus X-ray Sealed Tube Sources Manufactured by Incoatec

The concept of using a microfocus X-ray sealed tube source in combination with X-ray optics for diffraction experiments was first pioneered by U. Arndt (MRC-LMB, Cambridge) in the early 90’s. However, despite its impressive intensity, this first-generation microfocus source found limited acceptance due to relatively poor stability and very short tube lifetimes. Since then, there have been numerous research activities for finding suitable combinations of high-brilliant microfocusing sealed tube X-ray sources and X-ray optics. With respect to the X-ray optics, a breakthrough was the development of graded multilayer mirrors by H. Goebel (Siemens AG) in the mid 90’s. Multilayer mirrors have proven to be excellent beam-shaping devices for preserving the brightness of the microfocus X-ray source, resulting in a high intensity and good spectral purity. However, all microfocus X-ray tubes used for diffraction experiments at that time had in common that they were standard microfocus X-ray tubes, primarily designed for applications in non-destructive testing. This is because such tubes were readily available from several manufacturers, as non-destructive testing represents a much bigger industrial market compared to the market volume for X-ray diffraction instrumentation. Further, it is by no means easy to develop and manufacture a high-quality X-ray source, as one needs a sophisticated infrastructure and very specialized know-how. Therefore, it is not surprising that little to no efforts have been made so far for optimizing a microfocus X-ray source itself to match the requirements of the applications in diffraction. This is the main reason why Incoatec invested in establishing its own microfocus sealed tube development and manufacturing division IXT.

The Incoatec Microfocus Source IµS – Superb Performance and Proven Reliability
Incoatec’s microfocus source IµS consists of a low-power microfocus sealed tube which is combined with a state-of-the-art Montel multilayer mirror for 2D beam shaping. Since its introduction in 2006, the IµS has become the market-leading microfocus sealed tube X-ray source for many X-ray diffraction applications, such as protein and small molecule crystallography, high pressure research, microdiffraction, 2-dimensional X-ray diffraction (XRD2) and small angle X-ray scattering. Up to now, more than 1500 IµS sources have been sold and installed world-wide in academia and industry.
While the original 30 W IµS and the IµSHigh Brilliance contain third-party tubes designed primarily for NDT applications, the IµS 3.0 and the IµS DIAMOND II contain dedicated tubes which are optimized for diffraction and are “Made in Geesthacht”.

The ixtube – The First Masterpiece from Incoatec’s Tube Factory IXT
Over the past few years, Incoatec’s IXT team has subsequently explored and optimized several parameters critical to the performance of the source in X-ray diffraction applications, such as the take-off angle, e-beam focusing and filament shape. In a typical NDT tube operated in reflection mode, usually the footprint of the electron beam is very small, and the take-off angle is rather large (typically in the range of 20 to 50°, sometimes even larger), giving a large field of view required for radiography of larger objects.
However, for applications in X-ray diffraction, the source needs to “illuminate” only a small volume, as the typical sample sizes are in the range of a few mm down to a few µm. Thus, there is no need for a large field of view. One of the most important aspects for diffraction experiments is getting maximum intensity on the sample. Additionally, the X-ray beam needs to be monochromatic for most diffraction experiments, which requires the X-ray tube to be coupled to an X-ray optics that only filters the Ka radiation of the characteristic spectrum of the anode material pass. Multilayer X-ray optics have proven to be very efficient when it comes to monochromatize an X-ray beam while preserving most of the brilliance of the X-ray source. Due to the limited intrinsic view angle of a multilayer, a multilayer mirror typically “sees” only source sizes in the range of about 100 µm and smaller, which make them the perfect X-ray optics for microfocus sources.
The intensity of an X-ray tube can be increased by exciting a larger footprint on the anode by using an electron beam which is slightly elongated along the beam direction. In order to keep the apparent spot size of the X-ray tube small and tailored to the small acceptance angles of the multilayer optics, the take-off angle needs to be reduced, yielding a “concentrated” X-ray beam with a large number of photons within a solid angle (i.e. a high apparent brightness of the beam). However, the decrease in the take-off angle is limited by the increased self-absorption at lower take-off angles. Due to the small dimensions of the tube, forced air-cooling is sufficient to remove all waste heat.

This dedicated tube design is incorporated in our ixtube series for the IµS 3.0 making it the first tube that is optimized for crystallography. The IµS 3.0 is the 3rd generation of the IµS, yielding more than twice the intensity of other microfocus sealed tube sources on the market. Apart from the unique X-ray tube design, the mechanics, electronics and beam path have also been optimized to maximize the benefits for the user. The mechanical separation of tube and optics, and the reduction of the tolerance chain in the source mount makes the alignment extremly easy.

Shine Bright like a Diamond – The Diamond Hybrid Anode
The latest development in Incoatec’s X-ray tube factory is a new type of microfocus sealed tube with a unique anode technology, the diamond hybrid anode.
The diamond hybrid anode consists of an industrial diamond as heat spreader which is coated with a thin layer of the target material (e.g. Cu, Mo, Ag). It takes advantage of the exceptionally high thermal conductivity of diamond, which is up to 5 times higher than thermal conductivity of copper and the highest known conductivity of all bulk materials. This unique property of diamond makes it the material of choice for the thermal management in challenging applications where a high local heat load needs to be dissipated, such as in heat sinks for modern high-power microelectronic devices.
In the ixtube for the IµS DIAMOND II, the thin layer of the target material produces the X-rays while the underlying diamond substrate dissipates the heat load significantly more efficiently than a conventional bulk copper anode, as shown in the right figure comparing simulations of the heat dissipation. Consequently, the diamond hybrid anode can accept a higher power density in the focal spot on the anode without damaging the surface of the target layer, thus, generating more X-rays.
In order to exploit the full potential of the diamond hybrid anode, we have combined the diamond hybrid anode technology with a new high-brightness cathode delivering a dense electron beam with a very high emission rate. This new cathode has an extremely long lifetime beyond that of a classical W filament and is coupled with an active electron lens creating a very bright and uniform footprint on the anode. The IµS DIAMOND II delivers a superb intensity with an intensity gain of up to a factor of about two compared to the previous version of the IμS DIAMOND. The active electron lens is used to focus or defocus the electron beam, e.g. into a stand-by mode, while keeping the power constant. Thereby, thermal load changes between operational mode and stand-by mode are avoided, which will increase the lifetime of the tube.