Control system and data acquisition
Irradiation runs are computer controlled. The fluence of the irradiation is set and started by the operator and the run is stopped by the control computer when the programmed fluence has been reached. The run can also be stopped manually on demand of the client at any time. If needed, the flux can be stored every 0.5 second by the data acquisition.
A range telescope (Multi-Leave Faraday Cup, MLFC) can be used to measure proton energies. The MLFC consists of a stack of 64 aluminum sheets that are interspersed with Kapton foils. The absolute accuracy of the energy measurement with the MLFC is approximately 1%, the relative accuracy is about 0.02%.
Field shape and homogeneity
Field shape and homogeneity of the irradiation field are assessed with a Lanex scintillating screen. The image of the screen is captured with a CCD camera and is used to visualize and quantify the homogeneity of the irradiation field.
During the irradiation the flux is monitored with a Beam Intensity Monitor (BIM). This is an ionisation chamber positioned in the beam. The output current of the chamber is digitised into a pulse train, such that every pulse (monitor unit, MU) represents an amount of charge from the chamber.
Before an irradiation the BIM signal (in Monitor Units, MU) is related to the scintillator signal to obtain the flux calibration in protons per cm2 per MU. The proton flux at the centre of the irradiation field is measured using a Farmer chamber and/or with a 10 mm diameter scintillator detector.
This calibration is conducted for every field size and every energy used during an irradiation.
Monte Carlo simulations
A Monte-Carlo model of the irradiation set-up has been developed. This model is such that all components can be shifted in 3 dimensions allowing easy rearrangement of the setup of the beam line to assess e.g. proton fluxes and energy distributions at the position of the DUT.The model has been validated by a series of measurements.
|Laatst gewijzigd:||04 januari 2018 15:19|