Petenev, Y.; Feikes, J.; Klein, R.; Li, J.; Lubeck, J.; Matveenko, A.N.; Tamashevich, Y.; Thornagel, R.: Precise Measurement of Small Currents at the MLS. In: Yongbin Leng ... [Ed.] : Proceedings of IBIC2018, Shanghai, China, 09-13 September 2018. Geneva, Switzerland: JACoW Publishing, 2019. - ISBN 978-3-95450-201-1, p. MOPC03/118-121
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The Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute of Germany, utilizes an electron storage ring - the Metrology Light Source (MLS), located in Berlin, as a radiation source standard in the VIS, UV and VUV spectral range. In order to be able to calculate the absolute intensity of the radiation, the electron beam current has to be measured with low uncertainty. In this paper we focus on the measurement of the beam current in a range of several nA to 1 pA (one electron) by means of Si photodiodes, detecting synchrotron radiation from the beam. Electrons are gradually scraped out of the ring and the diode signal is analyzed afterwards. The exact number of stored electrons then can be derived from the signal. The measurement is carried out automatically with an in-house developed software.