| Paper |
Title |
Page |
| TUPCH189 |
FPGA-based RF Field Control at the Photocathode RF Gun of the DESY VUV-FEL
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1456 |
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- E. Vogel, W. Koprek, P. Pucyk
DESY, Hamburg
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At the DESY Vacuum Ultraviolet Free Electron Laser (VUV-FEL) bunch peak current and the SASE effect are (amongst other parameters) sensitive to beam energy and beam phase variations. The electron bunches are created in an rf gun, which does not have field probes. Variations of the gun rf field cause beam energy and phase variations. They have a significant influence on the overall performance of the facility. DSP based rf field control used previously was only able to stabilize the rf output of the klystron. This was due to the lack of processing power and the over-all loop delay. The controller was not able to provide satisfactory rf field stability in the gun. Replacing the DSP hardware by the new FPGA-based hardware Simulation Controller (SimCon), we are able to reduce the latency within the digital part significantly allowing for higher loop gain. Furthermore SimCon provides sufficient processing power for calculating a probe signal from the forward and reflected power as input for PI and adaptive feed forward (AFF) control. In this paper we describe the algorithms implemented and the gun rf field stability obtained.
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| THPCH085 |
The Longitudinal Coupled Bunch Feedback for HERA-p
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2985 |
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- M.G. Hoffmann, S. Choroba, F.E. Eints, U. Hurdelbrink, P.M. Morozov, J. Randhahn, S. Ruzin, S. Simrock, E. Vogel, R. Wagner
DESY, Hamburg
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A longitudinal broadband damper system to control coupled bunch instabilities has recently been constructed and installed in the 920~GeV proton accelereator HERA-p at the Deutsches Elektronen-Synchrotron DESY. This represents one of the attempts to increase the specific luminosity at HERA by reducing the bunch length. The final bunch length is defined by the initial emittance after injection and by the acceleration process where multiply occuring coupled bunch instabilities provoke bunch length blow up at discrete energies during the ramp. The actual feedback design consists of a fast, high precision bunch centroid phase detector, a 1~kW feedback cavity with 104~MHz centre frequency and 8~MHz bandwidth (FWHM), a I/Q-vector modulator, the low level digital FPGA-board with 14 Bit ADCs and DACs and a cavity transient diagnostics. The system measures the phases of all bunches and calculates corrections in real time (bunch spacing: 96~ns) which are then applied to the beam via a longitudinal kicker. The filter deals with a slowly changing synchrotron frequency (20-80 Hz).
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