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XFEL Operation OP Structure Accelerator Systems  · 

OPs-3xx: Accelerator Systems

OP-310: RF Gun

The RF-Gun system consists of a 1.3GHz 1.5 cell normal conducting copper cavity with a replaceable CsTe coated cathode plug. The RF is feed in through an RF window and an input coupler which does the transformation from a rectangular waveguide to the coaxial waveguide needed for the gun cavity.

  • Operation, maintenance and repair of the complete gun system.
  • The operating parameters have to be surveyed and adopted if needed
  • The cathode plugs have to be prepared and exchanged regularly
  • In case of damages parts of the system ( RF-window, cathode holder, coupler ) have to be exchanged
  • If necessary, the complete gun system has to be exchanged
  • Coordination of the support groups OP-210, OP-215, OP-315, OP-330 and OP-341

OP-315: Laser

The electron bunches of the XFEL are produced via photoemission from a Caesium-Telluride cathode inside the RF gun. The photons are generated by a UV laser which is able to produce the needed 2700 bunches in 10Hz repetition rate. The laser starts with an infrared wavelength which is then quadrupled to reach the necessary UV regime. A fraction of the IR laser power is separated and further amplified to produce IR laser pulses for the laser heater system.

  • Operation, maintenance and repair of the main- and the spare laser system.
  • In particular the frequency conversion crystals and the diagnostic cameras have to be replaced regularly
  • All optical components in the beamlines have to be surveyed and readjusted if necessary
  • 24 hours on-call service

OP-320: Laser Heater

The laser heater system is installed to avoid a breakup of the electron bunches in case that the energy distribution of the electrons is too narrow for the actual beam parameters. The heater system is able to broaden the distribution in a well-defined manner. By this procedure the SASE process can be stabilized and fluctuations in intensity can be reduced.
The system consists of an IR-laser amplifier, a 60m long vacuum beamline with 5 movable mirrors, two bread boards in the injector with laser diagnostics and moveable mirrors to tailor the beam. A feedback system is installed to stabilize the beam trajectory over the 60m length of the beamline. For the interaction with the electron beam an undulator magnet with moveable gap is placed in the injector beamline.

  • Operation, maintenance and repair of the complete laser heater system
  • All optical components in the beamlines have to be surveyed and readjusted if necessary
  • 24 hours on call duty

OP-325: Laser Based Synchronization

In the operation phase, the tasks of the OP-325 will be the operation, maintenance and repair of the optical synchronisation system that allows synchronising events along the complete facility to the 10 fs level. This includes 2 electronic hutches (XHIN, XHEXP) with 10 crates with specialised digital boards and monitor electronics, 4 master laser oscillators, 32 links, 8 laser to RF links for stabilizing the LLRF system, 5 laser to laser links to stabilize the injector and pump-probe lasers.

OP-330: Controls

  • Operation, maintenance and support of the accelerator control system (DOOCS) and its infrastructure
  • Operation, maintenance and support of the accelerator timing/event system and its infrastructure
  • Support, operation, maintenance of device servers for the various accelerator hardware in cooperation with other operation packages
  • Operation, maintenance and development of application software to improve operational stability and flexibility and answer to evolving needs

OP-335: Machine Protection

In the operation phase, OP-335 will be responsible for the operation of the machine protection system (MPS) of the European XFEL. In contrast to the personnel interlock system taking care that no access to the accelerator installation is possible during operation, so protecting the environment from the impact of accelerator, the MPS protects the accelerator hardware in case of component failures or operating errors. The system provides a distributed network of IO channels with fast, reliable, real time communication and minimum latency. All critical components are connected to the MPS, so that machine operation in case of failure is stopped immediately. Based on status information, beam in certain sections of the machine is allowed or inhibited, or restrictions on the number of bunches are applied. In addition to hardware failure signals, also beam based signals, like interlock signals from the about 500 beam loss monitors and about 40 charge monitors, interlocking on poor transmission are connected. The drive laser of the gun is, as well as shutters or RF systems are connected as fast actuators to stop beam operation. In this way the MPS takes care on the integrity of the machine status and enables operation with large average beam power. Without such a system operation would get unsafe and a high risk of self-destruction of the accelerator would arise.

OP-341: Vacuum

The European XFEL accelerator complex includes approximately 3.4 km of warm electron beam line vacuum system and about 1.2 km of superconducting linac with an isolation vacuum and RF power coupler vacuum system. All vacuum sections next to the linac are prepared and operated quasi particle-free. Special infrastructure was developed and is kept in operation in order to guarantee long time maintenance.

  • With the end of the XFEL construction about 800 ion getter pumps are used to keep the beam pipe vacuum at UHV level (10-9 to 10-7 mbar depending on the vacuum section). In addition more than 50 vacuum pump stations for the isolation vacuum consisting of turbo-molecular and rotary vane pumps are in operation.
  • All pump stations require preventive maintenance; approx. 3 - 5% of the pumps need to be replaced every year. Also ion getter pumps are not completely maintenance-free; a yearly failure rate of some very few percent is assumed.
  • The facility includes about 60 UHV vacuum valves for the beamline. According to experience with similar and partly identical units (FLASH, PETRA III) only a small fraction will need to be replaced during operation. Nevertheless, in case of exchange challenging installation work (local clean room, limited access) would have to be carried out. Thus experienced and well-trained personnel will be required.
  • The operation of the warm beam line vacuum system is expected to be relatively low-maintenance. Most challenging will be the exchange of broken components like beam diagnostics or even collimators. Supervision of the vacuum system is organized in on-call duty fashion.
  • A total of 1000 sensors are used to monitor the vacuum system (pressure, leak rate, residual gas analysis). All sensors are included in the vacuum control system and accessible to the vacuum experts; some fraction is displayed in the accelerator control room. Based on experience with other vacuum systems supervision is done with the help of on-call personnel.
  • Due to the size of the overall vacuum system further improvement but also development if expected during operation phase. Control of vacuum valves requires well-thought and redundant logic.
  • Preparation but also the summary of maintenance periods requires documentation which helps to successfully supervise the vacuum system.
  • Cleaning and assembly infrastructure set-up during the XFEL construction phase needs to be maintained in operation. Otherwise maintenance and repair during shutdown will be endangered

OP-345: Magnet Systems

In the operation phase, OP-345 is responsible for the operation of the magnet system, which consists of the magnets themselves plus their power supplies and magnet cables.
Magnets and power supplies need regular maintenance and repair. Some spare have to be on stock in order to continue operation immediately in case of a fatal error of a magnet or power supply.
The XFEL magnet system is a large system consists of 715 normal conducting magnets of 23 different types. The superconducting magnets built into the accelerator modules are part of OP-215: Modules. Of the 715 magnets, 275 magnets are corrector magnets which come in 5 different types, the remaining 440 magnets (of 18 types) are beam line magnets.

OP-350: Kicker Systems

In the XFEL 5 types of kicker systems are being used. The first type are the feedback kickers for the intra-bunch-train feedback (IBFB), the second are flat-top kickers for beam distribution, the third fast kickers for bunch pattern generation, the fourth are fast kickers for on-line beam diagnostics and the fifth is one dark current kicker in the gun section of the injector.

  • Operation, maintenance and repair of the kicker magnets and pulsers.
  • The feedback electronics and amplifiers for the IBFB are contained in OP-430 feedbacks. However OP-350 will support OP-430 in the operation, maintenance and repair of the IBFB kicker magnets.

OP-355: Beam Dumps

  • Supervision of the reliable operation of all XFEL beam dump systems; operating parameters are monitored continuously.
  • Permanent monitoring of the interface to the machine protection system.
  • Measurement of beam dump activation (together with radiation protection experts). Regular in-situ dump inspection during maintenance days.
  • Maintenance/repair of dump exchange and handling vehicles. Update of procedures for the dump exchange (based on experience gained).
  • Documentation and update of dump design drawings. Experience gained during operation will be used to prepare for the construction of replacement dumps, if needed.

OP-360: Standard Diagnostic

In the operation phase, the OP-360 will cover operation, maintenance of all systems of the standard electron beam dynamics, as well as optimization and R&D for the improvement of these systems. In the following the main systems counted as standard electron beam diagnostics will be named.

  • Beam Position Monitoring: About 500 devices deliver precise data on the electron beam orbit, and allow to optimize the beam transport with high precision and to readjust the orbit to well-prepared pre-sets for effective change of machine settings.
  • Charge Monitor System: About 40 installations deliver information about the transported charge along the accelerator. Measurements with high precision allow to control, optimize and stabilize charge levels to the stability required by the lasing process. High sensitivity allows for operation with extremely low charge, and to keep track on the transmission along the beamline. In addition specially developed dark current monitors look for parasitic currents emitted by thermal or field emission independently from the drive laser of the gun. These currents usually don´t match to the optics of the laser driven beam and can result in increased beam halo and losses along the accelerator. The dark current monitors allow to optimize the collimation scheme to minimize the effects of the dark current.
  • Beam Size Measurements, either screens or wire scanners. At about 75 stations, the beam size is measured, and provides the required data to keep track of the optics of the accelerator. They allow checking the machine model with the reality of the magnet settings and allowing optimization of the beam dynamics, as well as for measurements of projected or slice parameters.
  • About 500 beam loss monitors keep track of the beam loss inside the accelerator, and stop the beam transport within a bunch train in case losses exceed certain limits. This system protects the machine from mechanical damage by the beam. Furthermore it sets the limits such that activation of components close to the beamline can be kept within acceptable limits.
  • In addition to the systems mentioned before, the online dosimetry system does not take direct data from the beam, but keeps track of the accumulated radiation dose at certain positions in the accelerator installation. The measurement network is concentrated on the sensitive permanent magnets of the undulators and to measure inside the electronic racks, in order to ensure that unexpected high dose rates do not harm the sensitive electronics in the shielded cabinets. The system will indicate online, were additional shielding measures will be required and which operation modes will harm the undulator magnets.
  • In addition some more, smaller systems with low number of installations are provided, that are not further mentioned here.

OP-365: Special Diagnostic

OP-365 deals with the so called special diagnostics. The scope of this OP can be easily explained putting it in contrast to standard diagnostics. It deals with few specialized systems but with high complexity, while standard diagnostics provides the instruments required in bigger number of installation in the machine. OP-365 concentrates more on the longitudinal phase-space that requires very specialized installations to cope with fs electron pulse.
OP-365 specializes on the measurements and stabilization of arrival time and bunch shape or peak current respectively, and is therefore essential for stabilisation of photon intensity and pulse length within the given limits of the SASE process.


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