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MOZBC03 | Applications for Energy Recovering Free Electron Lasers | laser, electron, linac, controls | 132 | |||||
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The availability of high-power, high-brilliance sources of tunable photons from energy-recovered Free Electron Lasers is opening up whole new fields of application of accelerators in industry. This talk will review some of the ideas that are already being put into production, and some of the newer ideas that are still under development.
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MOPAN017 | Noise and drift characterization of direct laser to RF conversion scheme for the laser based synchronization system for FLASH at DESY | laser, injection, controls, electron | 182 | |||||
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Funding: This contribution is funded by the EUROFEL project. |
The next generation of FEL's (Free Electron Lasers) require a long and short term stable synchronisation of RF reference signals with an accuracy of 10 fs. For that an optical synchronisation system is developed for FLASH at DESY, that is based on optical pulse train which carry the timing information encoded in its precise repetition rate. The optical pulse train has to be converted into an RF signal to provide a local reference for calibration and operation of RF based devices. The drift and jitter performance of the optical to RF converter influences directly the phase stability of the accelerator. Three different methods for optical to RF converters, namely the direct photodiode detection, injection locking and a sagnac loop interferometer are currently under investigation. In this paper we concentrate on the jitter and drift performance of the direct photodiode conversion and show its limitations from measurement results. |
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MOPAN019 | Performance of the New Master Oscillator and Phase Reference System at FLASH | controls, monitoring, linac, klystron | 188 | |||||
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The master oscillator and phase reference system at FLASH must provide several rf reference frequencies to widely spread locations with low phase noise and small long term phase drifts. The phase noise requirements of the 1300 MHz reference is of the order of 0.1 deg. while short and medium term phase stability is of of the order of 0.1 deg. and 1 deg. respectively. The frequency distribution system employs a temperature stabilized coaxial line for rf power distribution and a fiber optic system for the monitoring of phase drifts. Presented are the the concept, design and performance measured in the accelerator environment.
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TUPMN012 | STARS - A Two-Stage High-Gain Harmonic Generation FEL Demonstrator | electron, laser, simulation, acceleration | 938 | |||||
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Funding: Bundesministerium fur Bildung und Forschung and the Land Berlin |
BESSY is proposing a demonstration facility, called STARS, for a two-stage high-gain harmonic generation free electron laser (HGHG FEL). STARS is planned for lasing in the wavelength range 40 to 70 nm, requiring a beam energy of 325 MeV. The facility consists of a normal conducting gun, three superconducting TESLA-type acceleration modules modified for CW operation, a single stage bunch compressor and finally a two-stage HGHG cascaded FEL. This paper describes the faciliy layout and the rationale behind the operation parameters. |
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TUPMS010 | Fabrication and Measurement of Efficient, Robust Cesiated Dispenser Photocathodes | cathode, laser, electron, ion | 1206 | |||||
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Funding: This work is funded by the Office of Naval Research and the Joint Technology Office. |
Photocathodes for high power free electron lasers face significant engineering and physics challenges in the quest for efficient, robust, long-lived, prompt laser-switched operation. The most efficient semiconductor photocathodes, notably those responsive to visible wavelengths, suffer from poor lifetime due to surface layer degradation, contamination, and desorption. Using a novel dispenser photocathode design, rejuvenation of cesiated surface layers in situ is investigated for semiconductor coatings building on previous results for cesiated metals. Cesium from a sub-surface reservoir diffuses to the surface through a microscopically porous, sintered tungsten matrix to repair the degraded surface layer. The goal of this research is to engineer and demonstrate efficient, robust, long-lived regenerable photocathodes in support of predictive photocathode modeling efforts and suitable for photoinjection applications. |
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TUPMS059 | LCLS Undulator Tuning And Fiducialization | undulator, alignment, electron, linac | 1320 | |||||
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Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515. |
The LCLS x-ray free electron laser project at SLAC requires 40 undulators: 33 in the beamline, 6 spares, and one reference undulator. A new facility was constructed at SLAC for tuning and fiducializing the undulators. The throughput of the facility must be approximately one undulator per week. Much effort has gone into automating the undulator tuning. Because of tight alignment tolerances, accurate techniques were developed to fiducialize the undulators. The new facility, the tuning techniques, and the fiducialization techniques will be discussed. |
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WEPMN011 | Multichannel Downconverter for the Next Generation RF Field Control for VUV- and X-Ray Free Electron Lasers | controls, laser, electron, insertion | 2071 | |||||
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Funding: We acknowledge financial support by DESY Hamburg and the EUROFEL project. |
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 critically influences the phase and amplitude stability. For the RF field control, a multichannel RF downconverter is used to detect the field vectors and control the vectorsum of 32 cavities. In this paper a new design of an 8 channel downconverter is presented. The downconverter frontend consists of a passive rf double balanced mixer input stage, intermediate filters and an integrated 16bit analog-to-digital converter (ADC). The design includes a digital motherboard for data preprocessing and communication with the controller. In addition we characterize the downconverter performance in amplitude and phase jitter, temperature drifts and channel crosstalk in laboratory environment as well as for accelerator operation. |
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THOAKI01 | Advances in Large Grain/Single Crystal SC Resonators at DESY | laser, electron | 2569 | |||||
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The main aim of the DESY large grain R&D program is to check whether this option is reasonable to apply for fabrication of ca. 1'000 XFEL cavities. Two aspects are being pursued. On one hand the basic material investigation, on the other hand the material availability, fabrication and preparation procedure. Several single cell large grain cavities of TESLA shape have been fabricated and tested. The best accelerating gradients of 41 MV/m was measured on electropolished cavity. First large grain nine-cell cavities worldwide have been produced under contract of DESY with ACCEL Instruments Co. All three cavities fulfil the XFEL specification already in first RF test after only BCP (Buffered Chemical Polishing) treatment and 800 degrees C annealing. Accelerating gradient of 27 - 29 MV/m was reached. A fabrication method of single crystal cavity of ILC like shape was proposed. A single cell single crystal cavity was build at the company ACCEL. Accelerating gradient of 37.5 MV/m reached after only 112 microns BCP and in situ baking 120 degrees C for 6 hrs with the quality factor higher as 2x1010. The developed method can be extended on fabrication of multi cell single crystal cavities.
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FROAC04 | Sub-10 Femtosecond Stabilization of a Fiber Link Using a Balanced Optical Cross Correlator | laser, polarization, feedback, electron | 3804 | |||||
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Synchronization of various components with fs stability is needed for the operation of free-electron-lasers such as FLASH or the European XFEL. One possibility to realize a high precision synchronization is to use a mode-locked Er-doped fiber laser as a master clock and to distribute ultra short laser pulses inside the machine using actively stabilized fiber links. In this paper we demonstrate the stabilization of a 300 m long fiber link with a self-aligned balanced cross-correlator using a single type II phase-matched PPKTP crystal. This approach allowed us to reduce the timing jitter added by the link to below 10 fs.
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FRPMN017 | Beam Position Monitor Calibration at the FLASH Linac at DESY | pick-up, undulator, electron, laser | 3937 | |||||
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In the FLASH (Free electron LASer in Hamburg) facility at DESY more than 60 beam position monitors (BPM) with single bunch resolution are currently installed, and more are planned for future installation. Their calibration has been initially made by measuring each electronics board in the RF laboratory. However the ultimate calibration of each monitor is made by measuring its response to beam movement. This is a time-consuming procedure depending on the availability and accuracy of other components of the machine such as corrector magnets. On the other hand it has the advantage of getting in one measurement the answer of the monitor with all its components and of being independent of the monitor type. The calibration procedure and particularities for various types of BPMs in various parts of the linac will be discussed. A procedure based on the response matrices is also now under study. This would significantly speed up the calibration procedure, which is particularly important in larger accelerators such as the European XFEL (X-ray Free Electron Laser), to be built at DESY.
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