| Superconducting Radio Frequency (SRF) cavities designed for proposed linear reaccelerators at the National Superconducting Cyclotron Laboratory (NSCL) have an unloaded quality factor (Q) on the order of 10 9. The high Q results in a very narrow bandwidth, so small perturbations in the cavity's resonant frequency result in large changes in the magnitude and phase of its electric field for a fixed frequency driving signal. As a result, it is necessary to use a controller that can compensate for perturbations as they occur.; This project develops a new digital low-level radio frequency (LLRF) controller for this application, including DSP-based hardware, software algorithms, and a graphical user interface. The digital LLRF controller provides two types of control over cavity perturbations. The LLRF implements a PID control on the cavity driving signal to compensate for nonlinearities and small random disturbances. Significant cavity detuning caused by narrow-band vibrations, referred to as "microphonics," are reduced by the LLRF controller using a piezoelectric tuner controlled by an adaptive feedforward cancellation algorithm.; The completed prototype is a small, standalone, economically viable, ethernet connected controller. Through a MATLAB interface, it will allow advanced algorithm development by control engineers who are not necessarily familiar with the low-level workings of the controller. |
