A sub-50 femtosecond bunch arrival time monitor system for

Abstract A bunch arrival time monitor using the future laser based synchronization system at FLASH has been developed. The signal of a beam pick-up with several GHz bandwidth is sampled by a sub-ps laser pulse using a broadband electro-optical modulator. Bunch arrival time deviations are converted into amplitude modulations of the sampling laser pulses which are then detected by a photo-detector. A resolution of 30 fs could be reached with the capability towards sub-10 fs level. In this paper we describe the design of the optical system and present recent results

STATUS OF THE FIBER LINK STABILIZATION UNITS AT FLASH

Abstract State-of-the-art X-ray photon science with modern freeelectron lasers (FEL) like FLASH (free-electron laser in Hamburg) and the upcoming European X-ray Free-Electron Laser Facility (XFEL) requires timing with femtosecond accuracy. For this purpose a sophisticated pulsed optical synchronization system distributes precise timing via lengthstabilized fiber links throughout the entire FEL. Stations to be synchronized comprise bunch arrival time monitors (BAM's), RF stations and optical cross-correlators (OXC) for external lasers. The different requirements of all those stations have to be met by one optical link stabilization unit (LSU) design, compensating drifts and jitter in the distribution system down to a fs-level. Five years of LSU operation at FLASH have led to numerous enhancements resulting in an elaborate system. This paper presents these enhancements, their impact on synchronization performance and the latest state of the LSUs

DEVELOPMENT OF AN ALTERNATIVE, PHOTODIODE-BASED, FEMTOSECOND STABLE DETECTION PRINCIPLE FOR THE LINK STABILIZATION IN THE OPTICAL SYNCHRONIZATION SYSTEMS AT FLASH AND XFEL

Abstract The fs-stable timing information in the optical synchronization system at FLASH and the upcoming European XFEL is based on the distribution of laser pulses in optical bers. The optical length of the bers is continuously monitored and drifts in signal propagation time are actively compensated in order to provide a phase stable pulse train at the end of the ber link. At present, optical cross-correlation is used to measure the optical length changes. To overcome some of the disadvantages of the current scheme, a different approach for the detection of the optical ber link length variation was developed. This new scheme uses 10 GHz photodiodes to measure the amplitude modulation of harmonics created by overlapping two pulse trains. The long-term stability of the prototype of this detector over 33 h was demonstrated to be below 5 fs (peakto-peak) with a rms jitter of about 0.86 fs. The detection principle itself is practically insensitive to environmental in uences and needs only about 10 % of the optical power, compared to the optical cross-correlator

Collimation system for the VUV free-electron laser at the TESLA test facility

To perform a proof-of-principle experiment for a Free Electron Laser operating at VUV wavelengths an undulator has been installed in the TESLA Test Facility linac phase I. To meet the requirements on the magnetic field quality in the undulator, a hybrid type structure with NdFeB permanent magnets has been chosen. The permanent magnets are sensitive to radiation by high energy particles. In order to perform the various experiments planned at the TESLA Test Facility linac, a collimator section has been installed to protect the undulator from radiation. In this thesis the design, performance and required steps for commissioning the collimator system are presented. To identify potential difficulties for the linac operation, the beam halo and the dark current transport through the entire linac is discussed. Losses of primary electrons caused by technical failures, component misalignments, and operation errors are investigated by tracking simulations, in order to derive a complete understanding of the absorbed dose in the permanent magnets of the undulator. Various topics related to a collimator system such as the removal of secondary particles produced at the collimators, generation and shielding of neutrons, excitation of wake fields, and beam based alignment concepts are important subjects of this thesis. (orig.)Available from TIB Hannover: RA 8919(2001-055) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Real-time sampling and processing hardware for bunch arrival time monitors at

Abstract Bunch arrival time monitors installed in several locations at FLASH measure the arrival time of an electron bunch relative to an optical reference. The optical reference for the monitors is provided by the optical synchronization system based on a laser pulse train with a repetition rate of 216 MHz and a pulse duration of around 200 fs FWHM. This pulse train is distributed to the arrival time monitors by transit-time-stabilized fiber links with a stability better than 10 fs. The monitors encode the electron arrival time into an amplitude modulation of the laser pulse train. These laser pulse amplitudes need to be sampled and processed together with additional input parameters. Because the arrival time information is used in a feedback loop to adjust the accelerator fields, the signal processing, calibration and transmission of the bunch arrival time information via a low-latency, high-speed link to an accelerator RF control station is needed. The most challenging problems related to the signal processing are the synchronization of several clock domains, regeneration and conversion of optical laser pulses, online calibration, and exception handling

COMMISSIONING OF THE LOW-NOISE MTCA.4-BASED LOCAL OSCILLATOR AND CLOCK GENERATION MODULE* 6: Beam Instrumentation, Controls, Feedback, and Operational Aspects T27 -Low Level RF MOPHA030 847

Abstract Within the Helmholtz Validation Fund Project "MicroTCA.4 for Industry", DESY together with collaboration partners from industry and research developed a compact fully MicroTCA chassis-integrated local RF oscillator module. The local oscillator and clock generation module generates a low noise local oscillator out of the global reference that is distributed over the accelerator. The module includes a splitting section which provides 9 local oscillator signals which are distributed over the RF-Backplane to the rear-transition modules. Similarly, the clock signal is also generated out of a single reference input by means of low-noise dividers. The clock is then fan-out to 22 differential lines that are routed over the RF backplane to the rear-transition modules. The functional block is implemented such that it fits in the rear slots 15 and 14 of a standard MTCA.4 crate. In the paper the commissioning results measured on the L3 lowlevel RF stations of the European XFEL will be presented. SYSTEM ARCHITECTURE The basic RF field detection scheme for the XFEL imposes specific requirements on the local oscillator (LO) and clock (CLK) generation circuits. The main design parameters are large number of tap-points and performance in terms of phase and amplitude stability. The decision was taken that each crate will have its own LO and CLK generation module. If one LO/CLK generation circuit would be serving multiple crates, this would cause issues with cable-drifts and reliability. On the other hand, having one LO/CLK generation circuits per one down-converter unit (8 field detectors) would increase the performance that could be achieved by vector-sum processing gain. The last option will be investigated in the future. The LO/CLK module presented in this paper is located in the rear side of a standard MTCA.4 crate in slot 15. It uses a dedicated RF backplane [1] for distributing the LO and CLK signals. This reduces the amount of cables needed. The crate environment provides also the power, hardware management and data communication to the module. One of the main functions of the LO/CLK generation module for the XFEL is to provide the local oscillator (LO) frequency at 1354 MHz. The LO frequency is generated by means of splitters and dividers as shown in Even if other architectures such as PLL-based circuits cover a wider frequency range of possible LO frequencies the method using dividers-only can practically achieve a lower residual phase noise while keeping the circuit simple. Because of the high number of tap-points the RF power before the splitting has to be in the order of 1 W which represents also a challenge in terms of shielding and DC power dissipation. The generation of the CLK signals is implemented via simple clock dividers. The reasons for such architecture are similar to the ones for the LO generation. HARDWARE OVERVIEW The module is composed of several subsystems. The carrier hosts the RF splitting section, the CLK signal generation, the digital management section, the application processing unit and the low-noise linear regulators. Other functionalities such as DC/DC converters, the temperature controllers and the local oscillator generation are moved off the carrier board on daughter cards and connected to the main board through multi-pin connectors. Carrier Board The carrier board's primary function is frequency and clock distribution to the RF back plane (see The carrier also provides DC power generation for the system via a shielded 'DC/DC-Mezzanine' card that hosts two 8 A switch-mode convertors. One convertor provides a 5.9 V output used by the numerous LDO's on both RF and carrier card, the other convertor provides a 5.0 V output used exclusively for temperature control via thermoelectric controllers (TEC's) and Peltier elements