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.
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.
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.
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.
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.
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.
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.
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.
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.
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.