• 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.

• H.W. Mostert, J.L. Conradie, M.A. Crombie, J.G. De Villiers, K. Springhorn
  iThemba LABS, Somerset West
• l. Boscagli, A. Dainese, M. Poggi, R. Ponchia
  INFN/LNL, Legnaro, Padova

Equipment for non-destructive, two-dimensional beam profile measurement has been developed for the 15 MV tandem accelerator at INFN, Legnaro and the K200 variable-energy, separated-sector cyclotron at iThemba Labs. Ions, produced by the interaction of the beam with residual gas, are accelerated in an electrostatic field towards microchannel plates (MCP) for signal amplification. With the first of the two prototypes that were built, ions are collected in an electric field between two parallel plates and after passing through an aperture in one of the plates, move through the electric field between two curved plates and bend through an angle of ninety degrees before reaching the MCP. The spread in ion energies provides the second position. In the second prototype two one-dimensional systems, rotated through ninety degrees with respect to each other, were installed close together. The measured beam profiles for both systems were compared with those of measurements with a nearby profile grid. Measurements were made on various beams and intensities between 10 and 10{00} nA. The beam position display with the MCP was calibrated to within 0.75 mm with the profile grid.