• Faraday cup
• LIGHT accelerator
• pre-amplifer
• proton beam current
• proton-therapy

This thesis project has been performed in A.D.A.M. (Applications of Detectors and Accelerators to Medicine) SA. A.D.A.M. is a Company “inspired” by CERN, founded in December 2007 to promote scientific know-how and innovations in medical technology. In particular, ADAM`s main activity is the design and construction of LIGHT, a linear accelerator for proton-therapy.
The thesis begins with a brief history of accelerators and their specific applications to cancer therapy, explaining why this therapy is developing so much in the last years and why LIGHT represents the state-of-the-art.
My work has been devoted to the design of a trans-impedance amplifier able to measure the current of the proton beam from a Faraday cup. As the range of beam current is large in LIGHT, the requirement on the dynamic range of the amplifier is correspondingly large, it runs between 10 nA and 1 mA, and therefore a multi-gain amplifier was proposed. The duration of the pulse beam current changes between 500 ns and 5 μs. The goal is to have a high bandwidth and high gain so as to be able to measure a statistically relevant number of samples on the flat top of the current, thereby increasing the accuracy of the measurement. Since the minimum pulse width is 500 ns, the output signal must have a rise-time on the order of 100 ns.
Simulations have been performed to reach the final choice of architecture and to realize the PCB. The simulations have been made using the LT-Spice program and the placement and the routing has been made using Altium Designer. The PCB was sent to Eurocircuit for production. The components have been soldered on the board and then the board tested.
The measurements of the amplifier for each implemented gain have been reported: linearity, frequency response, noise, offset and the rise-time. For the most challenging gain at 107, a bandwidth of 6 MHz was measured and a rise-time of 56 ns. The measured noise was 48 mV, equivalent to 4.8 nA. Considering that the minimum expected current in the LIGHT accelerator will be 320 nA, this noise should be low enough to give a good resolution.
In general, the results obtained by the measurements are close to our expectations (and those of simulation), allowing our amplifier to provide a suitable reading of the LIGHT beam current from the Faraday Cup.