Schweickhardt, Jens ; Klingbeil, Harald ; Frey, Michael ; Groß, Kerstin ; Domont-Yankulova, Dilyana (2020)
Broadband nonlinear modeling of RF amplifier-driven systems for multiharmonic predistortion of pulsed output signals.
In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 957
doi: 10.1016/j.nima.2020.163433
Article

Abstract

By applying pulsed voltages to particle beams in circular accelerators, the longitudinal distribution of the particles can be controlled. Specifically, so-called barrier bucket systems can be used to enclose the beam between two barrier pulses. The challenge in these barrier bucket systems is, that the high voltage pulses need to be of a certain shape with high signal quality in order to preserve a high beam quality. In order to generate the pulses, frequencies up to 100 times the fundamental frequency are required, leading to high signal distortion caused by frequency-dependent properties of the system and nonlinearities of the power amplifier at high output power. In order to reach the required well-defined output pulses, signal predistortion is indispensable. However, nonlinear PA modeling and signal predistortion tends to focus on modulated signals rather than pulsed voltages as it is mainly used in communication technology. Thus, many previously developed predistortion methods are not applicable for our application or have to be adapted for single voltage pulses. Here, we first define a distortion rate as a quantity for the deviation between the produced signal and the ideal output. In a second step, a Hammerstein model is developed for modeling both, the PA and the driven system together, and finally, the model is tested for two different PAs.

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