• D.T. Fourie, L.S. Anthony, A.H. Botha, J.L. Conradie, J.G. De Villiers, J.L.G. Delsink, P.F. Rohwer, P.A. van Schalkwyk
  iThemba LABS, Somerset West
• J. Dietrich
  FZJ, Jülich

Non-destructive beam position monitors (BPMs) have been in use at iThemba LABS for several years in the neutron therapy and radioisotope production beamlines, as well as in the transfer lines between the K200 separated-sector cyclotron and the two K8 injector cyclotrons. The sensitivity of these BPMs is limited by noise and pickup from the RF systems to about 300 nA in the high energy beam lines. For proton therapy, using the scattering method, position measurement at beam currents as low as 20 nA have to be made. A new and more sensitive BPM as well as the electronic measuring equipment, using RF pickup cancellation and improved filtering, have been developed and installed in the proton therapy beamline. The BPM, the electronic equipment and the results of measurements at beam currents down to 10 nA for 200 MeV protons are described.