The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created. The first operation of the European X-ray free-electron laser facility accelerator based on superconducting technology is reported. The maximum electron energy is 17.5 GeV. A laser average power of 6 W is achieved at a photon energy of 9.3 keV.

By end of 2016, the main accelerator of the European XFEL was completed. To build this complex machine in a minimum of time, certain management methods were introduced in mid 2015, which accelerated the installation process substantially. In the following 64 weeks additional 84 % of the main accelerator were set up. This was possible due to an improved planning, the reinforcement of two teams as well as a permanent controlling and optimizing of the installation process. In this paper, the installation process from July 2015 to end 2016 and the measures, which speeded up the workflow, are described.

The FLASH RF system consists of several RF stations, which provide RF power up to 10MW at 1.3GHz, 1.3ms and 10Hz repetition rate, each, for the superconducting cavities and the RF gun of the FLASH linear accelerator. During the last upgrade of the FLASH facility several modifications were made to the RF system. The oldest RF stations, constructed and manufactured by FNAL more than 15 years ago, were replaced. Since one additional superconducting accelerator module was added and one superconducting module and the RF gun were replaced, modification and rearrangement of the RF waveguide distributions were required. An XFEL type waveguide distribution for the new accelerator module ACC7 and a distribution without individual phase shifters for the exchanged module ACC1 were installed. A new waveguide distribution for the RF gun allows phase tuning by changing the gas pressure in the waveguides. It will also allow supplying the RF gun by a 10MW multi beam klystron instead of the currently used 5MW single beam klystron at a later point of time. This paper describes the exchanged and recently installed RF stations and the layout of the waveguide distribution system.

The FLASH RF system consists of several RF stations, which provide RF power up to 10MW at 1.3GHz, 1.3ms and 10Hz repetition rate, each, for the superconducting cavities and the RF gun of the FLASH linear accelerator. During the last upgrade of the FLASH facility several modifications were made to the RF system. The oldest RF stations, constructed and manufactured by FNAL more than 15 years ago, were replaced. Since one additional superconducting accelerator module was added and one superconducting module and the RF gun were replaced, modification and rearrangement of the RF waveguide distributions were required. An XFEL type waveguide distribution for the new accelerator module ACC7 and a distribution without individual phase shifters for the exchanged module ACC1 were installed. A new waveguide distribution for the RF gun allows phase tuning by changing the gas pressure in the waveguides. It will also allow supplying the RF gun by a 10MW multi beam klystron instead of the currently used 5MW single beam klystron at a later point of time. This paper describes the exchanged and recently installed RF stations and the layout of the waveguide distribution system.

The RF stations for the FLASH linear accelerator at DESY provide RF up to 10MW for 1.3ms and 10Hz at 1.3GHz for forty-eight superconducting cavities grouped into six cryogenic modules and for one normal conducting RF gun. A WR650 waveguide distribution system distributes the power generated by five RF stations using 5MW single beam and a 10MW multibeam klystron to the cavities and the gun. Since FLASH is based on the Tesla Test Facility, TTF, a number of different distribution layouts for the different modules and the gun have been developed and used over the years in terms of type of components and distribution scheme. This paper presents the layout and summarizes the experience with the existing waveguide distribution system.

A longitudinal broadband damper system to control coupled bunch instabilities (LMBF) has been installed in the 920 GeV proton accelereator HERA-p at the Deutsches Elektronen-Synchrotron DESY in Q4/2005. This was one of the attempts to increase the specific luminosity at HERA by reducing the bunch length.The feedback system is based on a single board FPGA (field programmable gate array) with two ADCs and 2 DACs (each 14 bits resolution) at 52 MHz sampling rate. It was fully automated, in order to relief the operator from manual control during system operation.During comissioning in Q1/2006 it turned out that the performance goals were reached and the noise introduced due to the feedback corrections and the 1 kW power amplifier was not as much a problem as expected. The proton bunch length is significantly reduced as well as the lengthening of the bunches over runtime since all formaly occuring coupled bunch instabilities could sufficiently be suppressed during the enegergy ramp and the following luminosity run.System optimization points were found in automatic gain adjustment during acceleration ramp, oscillation level triggering and timing of kicker pulse to bunch.

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). The goal of this system is to reduce the bunch length and thus increase specific luminosity at HERA–p. Within the control system a kicker cavity is used as an actuator. The original aspect of this cavity lies in the simple geometry with no need for vacuum inside the cavity and high shunt impedance despite an internal ferrite load. The ferrite load is successfully used to dampen higher order modes down to Q <50 while the fundamental mode is damped by less than 2 dB. While nominal input power is rated at 1 kW the cavity is prepared to handle beam loading. In spite of power requirements and ferrite load the cavity needs no active cooling. It can be tuned in resonance frequency and bandwidth over a range of 96 ...1 05 MHz and 7.8. ..1 2 MHz respectively and in consequence provides an optimal actuator for the particle beam control system.

A longitudinal broadband damper system to control cou- pled bunch instabilities has been developed and installed in the 920 GeV proton accelerator HERA-p at DESY. The control path consists of a FPGA-based digital controller, a vector modulator, a 1 kW power amplifier, a kicker-cavity and the beam itself. The bunch phase signals are sampled by a digital FPGA board with 14 Bit ADCs and 10.4 MHz. Phase calculation for all bunches and offset correction is done by a digital filter realized in FPGA software. The filter has to deal with a slowly changing synchrotron fre- quency. Here we considered a filter design which treats each of maximum 220 bunches as an independent oscilla- tor which has to be damped. With the FPGA-board output signals a 104 MHz sine wave is modulated. The resulting logitudinal correction kick signal is provided by the kicker- cavity to kick the proton bunches each with its correction kick voltage. Besides the technical details we present first operational experience and the actual system performance in a series of 3 papers (see also (1, 2)).

1. ABSTRACT This report describes the design of a phase stable Fiber Optic (FO) link for the TESLA technology based projects. The concept of this long optical link, with a feedback system suppressing long term drifts of the RF signal phase is described. Stability requirements are given and most important design issues affecting the system performance are discussed. The technical design issues of system components like laser transmitter and optical phase shifter are described in detail. Last sections depict the software developed for system control and experimental results obtained after system was assembled.

The UV Free-Electron Laser (UVFEL) and The TeV-Energy Superconducting Linear Accelerator (TESLA) projects will require phase synchronization of 0.1 ps short term (millisecond), 1 ps short term (minutes) and 10 ps long term (days). The stringent synchronization requirement of 10fs was given for the X-Ray Free- Electron Laser (XFEL). To fufill this requirement the XFEL may use a fiber laser as reference generator. But this requirement applies for a special location only, therefore the RF phase reference distribution system developed UVFEL and TESLA will also be used in the XFEL. The RF phase reference distribution system must deliver phase stable signals to hundreds of stations over a length of 33 km. Long, optical fiber based links are planned to be an important part of the entire distribution system. This paper describes the concept of a long optical link, with a feedback system suppressing long term drifts of the RF signal phase. Stability requirements are given and most important design issues affecting system performance are discussed. Finally, an experimental setup and measurement results demonstrating system performance is shown.

A longitudinal broadband damper system to control cou- pled bunch instabilities has recently been constructed and installed in the 920 GeV proton accelereator HERA-p at the Deutsches Elektronen-Synchrotron (DESY). The goal of this system is to reduce the bunch length and thus in- crease specific luminosity at HERA-p. Within the con- trol system a kicker cavity is used as an actuator. The original aspect of this cavity lies in the simple geometry with no need for vacuum inside the cavity and high shunt impedance despite an internal ferrite load. The ferrite load is successfully used to dampen higher order modes down to Q <50 while the fundamental mode is damped by less than 2 dB. While nominal input power is rated at 1 kW the cavity is prepared to handle beam loading. In spite of power re- quirements and ferrite load the cavity needs no active cool- ing. It can be tuned in resonance frequency and bandwidth over a range of 96 ...1 05 MHz and 7.8. ..1 2 MHz respec- tively and in consequence provides an optimal actuator for the particle beam control system.