Block diagram of the MkV feed-forward system: The signal chassis demodulates RF pulses sampled from the high power linac drive. A control computer acquires the pulse data from a digital oscilloscope and generates compensation waveforms. Two arbitrary waveform generators apply the correction to the respective amplitude or phase modulator for all subsequent pulses.
Feed-forward system hardware layout: The RF signal chassis contains the reference amplifier, mixers, digital attenuator, and phase shifter. Power supplies and computer interface modules are also included.
Feed-forward GUI: The graphical user interface (GUI) for the feed-forward system is implemented in wxPython 8 running on Linux. The upper plot shows the raw sampled in-phase and quadrature signals, while the bottom plot shows the reconstructed amplitude and phase. System commands are issued using the buttons at the bottom of the window.
Effect of phase compensation: The application of a feed-forward phase compensation waveform results in an 80% reduction in phase ripple.
Laser spectrograms: Measured effect of feed-forward on laser performance (a) with phase compensation off and (b) with phase compensation enabled.
Measured effect of the feed-forward system on laser performance. (a) The laser pulse power and (b) spectrum are computed as the integrals of the spectrogram plot in λ and t, respectively. The compensation lengthens the pulse duration by 40%, while the spectrum narrows by 20%.
Simulated laser cavity detuning curves for uncompensated phase perturbation (boxes), compensated phase perturbation (circles), and no phase perturbation (diamonds).
Simulated laser pulse power evolution with (solid) and without (dashed) electron beam phase compensation.
Simulated laser wavelength evolution with (solid) and without (dashed) electron beam phase compensation.
Effect of amplitude compensation: Feed-forward phase and amplitude compensation result in an 85% RF power ripple reduction.
Measured electron beam energy spectrum with no compensation (dotted), phase compensation alone (dashed), and phase and amplitude compensation (solid).
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