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

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

Inclusive production of charged pions, kaons and protons in #UPSILON#(4S) decays

SIGLEAvailable from TIB Hannover: RA 2999(92-155) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Observation of the decay D_s_1(2536) #-># D"*"0K"+

SIGLEAvailable from TIB Hannover: RA 2999(92-124) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

New results on D"0 decays

SIGLEAvailable from TIB Hannover: RA 2999(92-077) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

A measurement of the tau mass

SIGLEAvailable from TIB Hannover: RA 2999(92-086) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Measurement of the decay #tau#"-#->##rho#"-#nu#_#tau#

SIGLEAvailable from TIB Hannover: RA 2999(92-082) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Production and decay of the charged D* meson in e e annihilation at 10 GeV centre-of-mass energy

Copy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Analysis of the decay #tau#"- #-># #pi#"-#pi#"-#pi#"+#nu#_#tau# and determination of the a_1(1260) resonance parameters

SIGLEAvailable from TIB Hannover: RA 2999(92-125) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman