RF Field Control

One of the LLRF system's core functions is controlling the RF field for particle beam acceleration. An RF controller implements feedback or feedforward algorithms, regulating the RF field to follow set points or stabilizing it against disturbances. This chapter will discuss the principles of GDR, SEL, and PLL control strategies. Several widely used feedback and feedforward algorithms will be introduced. These algorithms can be applied to practical LLRF systems directly. We will also discuss the cavity resonance control, which keeps the cavity on-resonance and is essential to enhance the performance of RF field controls.