The German Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), is a substantial research operation, employing around 1,100 staff and with an annual budget in excess of 100 million Euros. HZB operates two large scale scientific facilities for investigating the structure and function of matter: the research reactor BER II, (for experiments with neutrons), and the electron storage ring known as BESSY II, designed to produce an ultra-bright photon beam in a spectrum ranging from Terahertz to hard X-rays. Both facilities provide research opportunities for the study of matter and provide a highly specialised sample environment in which experiments can be carried out under the most sophisticated conditions. Included amongst these are ultra high vacuum (UHV), together with a cryogenic environment, high magnetic fields, low temperatures and high pressure.
Arguably, any one aspect of these test conditions presents significant challenges for bearings, but in some cases matrices of more than three elements are experienced in a single research programme. The Cryomanipulator Pente.Ax, designed by Dr Andrei Varykhalov, is a unique device which allows scientists and researchers to expand the envelope of spin-and angle-resolved photoelectron spectroscopy. Normal bearings simply wouldn’t last in such an environment, where temperatures of -249°Celsius are always present, so Carter supplied UNASIS ceramic bearings for the cryomanipulator which are designed specifically for use in ultra-low temperature environments.
The Pente.Ax Cryomanipulator, as Dr. Varykhalov explains, determines the electric, magnetic and optical properties of solids. Angle and spin-resolved photoelectron spectroscopy is the most powerful experimental technique for this type of investigation into the electronic and magnetic properties of crystals, using, in the core, a photoelectric process.
Part of this experimental method requires very precise positioning of the investigated sample, and linear translations are needed to adjust the sample in the focus of electron spectrometer. Absolute positional accuracy – to within prescribed microns – is also required to be able to select the spot of analysis on the sample surface. These angular rotations allow researchers to select the directions in which the properties of electronic bands in the crystal are measured, and clearly call for a level of bearing precision way beyond that which even the best ‘standard’ bearings are capable of achieving.
To cope with both the ultra-low temperatures and the absolute positional precision required for the application, Carter supplied ceramic Silicon Nitride (Si3N4) UNASIS bearings to HZB. They are specifically designed to operate without ongoing lubrication in an ultra-high vacuum environment and at cryogenic temperatures, being super-cooled by liquid helium. Carter Manufacturing provided pre-project detailed analyses as the initial design was being formalised, and then went on to deliver both the special UNASIS low-temperature bearings and full ongoing technical support for the project. The bearings selected for the HZB research project have a much longer life thanks to the properties of the silicon nitride ceramic material which both the races and balls were produced from.
According to the project leader Dr. Varykhalov, the UNASIS bearings operating in the cryogenic vacuum have proved to be mechanically robust and 100% reliable, despite the manipulator being used almost continuously in the experiments.
