SLIM (secondary emission monitor for low interception monitoring) an innovative non-destructive beam monitor for the extraction lines of a hadrontherapy centre

Real time monitoring of hadrontherapy beam intensity and profile is a critical issue for the optimisation of dose delivery to carcinogenic tissue, patient safety and operation of the accelerator complex. For this purpose an innovative beam monitor, SLIM (secondary electron emission for low interception monitoring) is being developed in the framework of the EC-funded SUCIMA (silicon ultra-fast cameras for electrons and gamma sources in medical application) project The detector system is based on the secondary emission of electrons by a non-perturbative, sub-micron thick Al foil placed directly in the extracted beam path. The secondary electrons, accelerated by an electrostatic focusing system, are detected by a monolithic silicon position-sensitive sensor, which provides the beam intensity and its position with a precision of 1 mm at a 10 kHz frame rate. The results of the laboratory tests of the first system prototype with thermoionic electrons emitted from a hot Tungsten wire are presented together with the measurements performed on a low intensity hadron beam at the Cyclotron of the Joint Research Centre in Ispra.