LNL Annual Report 2004

Linac accelerators based on independently phased resonators require precise phase shifters to setup the reference phase of each cavity with respect to the master oscillator. In a linac like ALPI, that has more than 80 resonators in operation (including those of the new PIAVE injector), the cost of such phase shifters represents a significant fraction of the cost of the overall RF control system. In ALPI we have used Merrimac digital phase shifters (series PTB-84A and PTB-84B) at frequencies of 80 and 160 MHz. The cost of these components is very high (around 5000-6000 USD, depending on the frequency and the quantity) but it is justified by the high precision and stability of these components. After many years of Linac operation we reconsidered the question if phase shifters with less performing characteristics – but also a lower price – could be suitable for providing a phase reference signal to our resonator controllers. Following the promising tests we made on a vector modulator realized using a high speed analog multiplier [1], we decided to further extend that design and use it as building block for a digitally controlled phase shifter. This paper describes the realization of such device and compares its performance to a Merrimac PTB-84B model.