A New Device for Bimorph Mirrors Technology: the A1902BS Bipolar Power Supply System

An important feature of X-ray Piezoelectric Bimorph Mirror (PBM) is the possibility to continuously vary its curvature (dynamical bending); this ability allows the precise adjustment of their optical properties to different beamline geometries and permits the variation of the grazing angle of incidence or to optimize the focal spot dimensions in the experimental chamber. When a driving voltage is applied at a particular position of the mirror, one of the piezo plates shrinks while the other one expands and, as an example, it can result in a purely spherical bending of the device if the same voltage is applied to all electrodes. The applied voltages have to be kept extremely stable on a very long time scale (weeks or even months). This means that the performance and the general behavior of the mirror are strongly dependent on the power supply used to drive it. For this challenging application, Sincrotrone Trieste developed a particularly stable high voltage bipolar power supply system (ranging from -2kV to + 2kV, zero crossing). This system is controlled by an Intel SBC board and accessible via Ethernet through any common web browser, Lab VIEW client or some of the most popular synchrotron facility control systems (Epics and Tango for instance). The maximum drain and source capabilities are 500uA per channel. Voltage monitoring is achieved by sensing the real output and feeding it to a true 16bit ADC. The voltage resolution achieved is about 60mV while the current resolution is about 60nA. Noise and residual ripple (rms) are better than 15ppm/FS and, most important, the long term stability (1 week observation) is better than 100ppm/FS. Some metrological measurements, on different bimorph mirrors, was carried out at the optical laboratory of Elettra. These measures demonstrate the high level of resolution and stability of the power supplies, able to change considerably the radius of curvature of the mirror and, in the meantime, correct even very small shape error