• R.M. Seraphim, O.R. Bagnato, F.H. Cardoso, R.H.A. Farias, R.O. Ferraz, H.G. Filho, F. R. Francisco, G.R. Gomes, S.R. Marques, R.T. Neuenschwander, F. Rodrigues, A.L. Rosa, M.B. Silva, M.M. Xavier
  LNLS, Campinas
• P.F. Tavares
  Karlsruhe Institute of Technology (KIT), Karlsruhe

In the beginning of 2008 an upgrade of the beam position monitors (BPMs) of the Brazilian Synchrotron Light Source (LNLS) electron storage ring was decided and scheduled as part of the continuous effort to improve the electron beam orbit stability. The objective was to replace most of the 24 BPMs installed in the storage ring and install new radiation absorbers inside the vacuum chamber. The original stripline BPMs were sensitive to temperature changes in the vacuum chamber. Heat, which induced mechanical stress in the striplines, could lead to fluctuations in the position readings thereby disturbing the orbit stability. The problem affected differently the BPMs. Although not a great issue during a typical user shift, the perturbations could pose some problems for the most sensitive experiments. One third of the BPMs were replaced in October 2008 and the remaining in October 2009. Thus, this large vacuum intervention aimed at improving the thermal and mechanical stability of the electron beam orbit measurement system. Finally, it will be presented the main changes made in the vacuum chambers and a survey of the evolution of the vacuum system after both interventions.