Feedforward Control of Accelerator RF Fields

A new and very effective technique for accelerator field control is demonstrated, using a feedforward control loop to complement a standard feedback controller. The accelerated beam current envelope, which acts as a load disturbance on the accelerator field amplitude and phase, is detected upstream from the module to be controlled. Due to differences in propagation velocity in the accelerator and external cables, true anticipating control is possible by feeding the current signal forward to the controller. In tests with full beam loading (22%) in the first 201.25 MHz tank at LAMPF, peak amplitude error was reduced to 0.4% and settling time to 20 ¿sec at beam turn-on.