SYSTEM IDENTIFICATION FOR THE DIGITAL RF CONTROL SYSTEM AT THE TESLA TEST FACILITY

The rf control system for the TESLA Test Facility employs a digital feedback system to provide flexibility in the choice of feedback algorithms and extensive diagnostics for rf sys-tem operation and exception handling. The control algo-rithm makes use of the state space formalism where the state describes the real and imaginary part of the cavity voltage (vector of the accelerating field) and the cavity de-tuning. The cavity detuning – which is time dependent due to the dynamics of lorentz-force-detuning in a pulsed cav-ity – can not be measured directly. Knowledge about the time-varying cavity detuning and other rf system parame-ters such as beam phase are derived by application of sys-tem identification to the uncalibrated measured cavity field and incident and reflected wave. In this process the calibra-tions for incident and reflected wave are determined which includes compensation for the finite directivity of the direc-tional couplers.