Digital I/Q Demodulator* SLAC-PUB-95-6857
I/Q demodulation is a common and useful RF signal processing technique used in charged-particle accelerators. When implemented with conventional analog RF components, a number of inherent errors can degrade the I/Q Demodulator performance, including gain balance, quadrature-phase balance, DC offsets, impedance match, and carrier leakage. Recent advances in high-speed analog-to-digital converters allow the I/Q demodulator to be implemented digitally, greatly reducing these systematic errors. This paper describes the design of a digital I/Q demodulator that will be applied to the PEP-II B factory.
rf feedback development for the PEP-II B factory
In PEP-II heavy beam loading along with a relatively long revolution period combine to strongly drive lower coupled-bunch modes through interaction with the fundamental cavity mode. Feedback techniques can be applied to reduce the cavity impedance seen by the beam. Several RF feedback loops are planned to reduce the growth rates down to a level which can be damped by the relatively low power bunch-by-bunch longitudinal feedback system[l]. This paper describes the RF feedback loops as well as hardware tests using a 500 kW klystron, analog and digital feedback loops, and a low power test cavity.
RF feedback simulation results for PEP-II
A model of the RF feedback system for PEP-II has been developed to provide time-domain simulation and frequency-domain analysis of the complete system. The model includes the longitudinal beam dynamics, cavity fundamental resonance, feedback loops, and the nonlinear klystron operating near saturation. Transients from an ion clearing gap and a reference phase modulation from the longitudinal feedback system are also studied. Growth rates are predicted and overall system stability examined.