Beamline Description

The beam position monitor

 A photon beam position monitor (BPM) is installed at the the beginning of the beamline. The device is based on four insulated Mo photoemitting plates, installed upstream of the beamline optics at 12 meters from the source. The current drained from the plates, typically of the order of some tens of uA, is read by four floatable ammeters. The BPM is currently used in differential mode operation, i.e. reading the normalized difference between up and down plates S=(Iup-Idown)/(Iup+Idown). This mode features a sensitivity of the order of about 1 um. A quantitative model connecting the energy shift with beam height was deduced (see A. Giglia et al., The beam position monitor of the BEAR beamline,  Rev. Sci. Instrum. 76, 063111 (2005).

Picture of the Photon BPM


BEAR is installead at the 8.1 exit of Elettra. The optical layout is not based on entrance slits. The front end is equipped with a pinhole copper mask at 2.6 meters from the synchrotron source. The left pinhole (see picture) corresponds to the Bear exit.

Picture of the pinhole


Ultima modifica il Martedì, 23 Febbraio 2021 14:12