Feed forward control: An implementation at CIRFEL
- Northrop Grumman Advanced Technology and Development Center, Princeton, NJ (United States); and others
An integral part of the Compact InfraRed Free Electron LASER (CIRFEL) is control of the phase and amplitude stability in the RF power system. We have implemented such a Feed Forward system using the LabView software package, by National Instruments. We will discuss implementation and performance data of the Feed Forward control of the RF power system at CIRFEL. We will also briefly discuss some conditions under which the problem is ill-conditioned, and what idealizations can be made to remedy these ill-conditioned systems. Using an arbitrary function generator, we generate a driving signal for a voltage-controlled attenuator at the input side of the RF system, and we monitor the RF voltage in cell I of the photocathode gun using a digital storage oscilliscope in averaging mode. The system is stable enough to use data from one shot to modify the inputs for future shots. After downloading the averaged data to a personal computer via a GPIB (IEEE 488) bus, we use a simple linear transformation on the difference waveform between the current shot and the target to produce a correction signal. This signal is added to the driving signal in the arbitrary function generator, and the process is repeated until we get the flatness we need in the output signals from cell 1. The system for phase control is similar, with a voltage-controlled phase shifter replacing the attenuator, and monitoring of the RF phase in cell I replacing the monitoring of RF voltage. By repeatedly alternating between correcting the RF voltage (equivalent to correcting the RF power) and RF phase in cell 1, we are able to achieve simultaneous phase variations of <{+-}1{degrees} and amplitude variations of <{+-}0.1% over a 3{mu}sec pulse.
- Research Organization:
- Brookhaven National Lab., Upton, NY (United States)
- OSTI ID:
- 238678
- Report Number(s):
- BNL--61982-Absts.; CONF-9508156--Absts.; ON: DE96002729
- Country of Publication:
- United States
- Language:
- English
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