| Paper |
Title |
Page |
| TUPCH187 |
DSP-based Low Level RF Control as an Integrated Part of DOOCS Control System
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1450 |
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- V. Ayvazyan, A. Brandt, O. Hensler, G.M. Petrosyan, L.M. Petrosyan, K. Rehlich, S. Simrock, P. Vetrov
DESY, Hamburg
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The Distributed Object Oriented Control System (DOOCS) has been developed at DESY as a control system for TTF/VUV-FEL. The DSP based low level RF control system is one of the main subsystems of the linac. Several DOOCS device servers and client applications have been developed to integrate low level RF control into the TTF/VUV-FEL control system. The DOOCS approach defines each hardware device as a separate object and this object is represented in a network by a device server, which handles all device functions. A client application can have access to the server data using the DOOCS application programming interface. A set of generic and specially devoted programs provide the tools for the operators to control the RF system. The RF operation at the linac is being automated by the implementation of DOOCS finite state machine servers.
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| TUPCH188 |
Phase Stability of the Next Generation RF Field Control for VUV- and X-ray Free Electron Laser
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1453 |
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- F. Ludwig, M. Hoffmann, H. Schlarb, S. Simrock
DESY, Hamburg
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For pump and probe experiments at VUV- and X-ray free electron lasers the stability of the electron beam and timing reference must be guaranteed in phase for the injector and bunch compression section within a resolution of 0.01 degree (rms) and in amplitude within 1 10-4 (rms). The performance of the field detection and regulation of the acceleration RF directly influences the phase and amplitude stability. In this paper we present the phase noise budget for a RF-regulation system including the noise characterization of all subcomponents, in detail down-converter, ADC sampling, vector-modulator, master oscillator and klystron. We study the amplitude to phase noise conversion for a detuned cavity. In addition we investigate the beam jitter induced by these noise sources within the regulation and determine the optimal controller gain. We acknowledge financial support by DESY Hamburg and the EUROFEL project.
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| TUPCH190 |
Universal Controller for Digital RF Control
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1459 |
| |
- S. Simrock
DESY, Hamburg
- W. Cichalewski, M.K. Grecki, G.W. Jablonski
TUL-DMCS, Lodz
- W.J. Jalmuzna
Warsaw University of Technology, Institute of Electronic Systems, Warsaw
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Digital RF control systems allow to change the type of controller by programming of the algorithms executed in FPGAs and/or DSPs. It is even possible to design a universal controller where the controller mode is selected by change of parameters. The concept of a universal controller includes the self-excited-loop (SEL) and generator driven resonator (GDR) concept, the choice of I/Q and amplitude or phase control, and allows for different filters (including Kalman filter and method of optimal controller synthesis) to be applied. Even time-varying mixtures of these modes are possible. Presented is the implementation of such a controller and the operational results with a superconducting cavity.
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| TUPCH191 |
Considerations for the Choice of the Intermediate Frequency and Sampling Rate for Digital RF Control
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1462 |
| |
- S. Simrock, M. Hoffmann, F. Ludwig
DESY, Hamburg
- M.K. Grecki, T. Jezynski
TUL-DMCS, Lodz
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Modern FPGA-based rf control systems employ digital field detectors where an intermediate frequency (IF) in the range of 10 to more than 100 MHz is sampled with a synchronized clock. Present ADC technology with 14-16 bit resolution allows for maximum sampling rates up to 250 MHz. While higher IF's increase the sensitivity to clock jitter, lower IF frequencies are more susceptible to electromagnetic noise. The choice of intermediate frequency and sampling rate should minimize the overall detector noise, provide high measurement bandwidth and low latency in field detection, and support algorithms for optimal field estimation.
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| THPCH084 |
Control Path of Longitudinal Multibunch-feedback System at HERA-p
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2982 |
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- F.E. Eints, S. Choroba, M.G. Hoffmann, U. Hurdelbrink, P.M. Morozov, J. Randhahn, S. Ruzin, S. Simrock
DESY, Hamburg
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A longitudinal broadband damper system to control coupled bunch instabilities has been developed and installed in the proton accelerator HERA-p at the DESY. The control system consists of a control path and a Fast Diagnostic System (FDS) for oscillation diagnostic. The control path consists of FPGA-based digital controller, vector modulator, 1kW power amplifier, kicker-cavity and beam. In the FDS, the bunch phase signals are sampled by a digital FPGA board with 14Bit ADC (controller) with a sampling frequency of 10.4MHz. Phase calculation for all bunches and offset correction will be done by FPGA software which includes a digital filter. The filter has to be able to deal with a slowly changing synchrotron frequency. Here we consider a filter design which treats each of maximum 220 bunches as an independent oscillator which has to be damped. More sophisticated mode filter algorithms may be required to get better noise performance. The FPGA-board output signal modulates a 104 MHz sine-wave. The resulting logitudinal correction kick signal is provided by the kicker-cavity. Beside the technical details we present first operational experience and the actual system performance.
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| THPCH085 |
The Longitudinal Coupled Bunch Feedback for HERA-p
|
2985 |
| |
- 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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| THPCH175 |
Automatic Resonant Excitation Based System for Lorentz Force Compensation for Flash
|
3206 |
| |
- P.M. Sekalski, A. Napieralski
TUL-DMCS, Lodz
- S. Simrock
DESY, Hamburg
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The cavity is the key element of each linear accelerator used for high-energy physics purpose. The resonant frequency of cavities depends on its shape. Due to the pulse operation, they are deformed by dynamic Lorentz force (LF) caused by accelerating electromechanical field. As a consequence, the cavities are not working on resonance but they are detuned from master oscillator frequency by few hundreds of Hertz depending on accelerating field gradient. The paper presents an automatic control system for LF compensation applied to fast tuning mechanism CTS. The active element is multilayer low-voltage piezoelectric stack (EPCOS). The resonant excitation with adaptive feed forward algorithm is used to drive the actuator. Test performed at FLASH (former name VUV-FEL) on cav5/ACC1 showed that detuning during flat-top period (800us) might remain below 10Hz for accelerating field gradient of 20MV/m.
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