Influence of the Droop and Ripple of Modulator on Klystron Output

The variations of the phase and amplitude of klystron output due to the change in klystron cathode voltage is investigated in this note. The mechanism and the effectiveness of the feedback control to suppress the variations are given. To understand the limitation of the feedback, both proportional controller and proportional-integral controller used in feedback loop are simulated and analyzed respectively for superconducting cavity and normal conducting cavity. The tolerances of the droop and ripple in cathode voltage are shown according to the data and results obtained. All the simulations and calculations are performed with MATLAB. The data and results are listed in detail so as to enable comparison with further studies and measurements at ESS.