First electrons in European XFEL

Succesful acceleration of first electrons in XFEL electron injector is a major milestone in development of the European Free-Electron X-ray Laser. Eu-XFEL Accelerator Consortium has assigned NCBJ the task to produce and deliver some 1.2 million Euro worth components of control circuitry to-be-deployed at XFEL research stands. The assignment is a sure sign of recognition of capabilities of Polish science/industry.

Electron injector is the first accelerating module of the European XFEL laser under development in DESY Hamburg since 2013. It’s first successive run was announced on December 21, 2015. Along its 45 metre long beamline electrons are accelerated to nearly the speed of light. Electron energy will be gradually increased up to 20 GeV across a 2-kilometre long superconducting linear accelerator still under construction. A beam of high energy electrons passing through a series of highly precise magnets of cyclically opposite polarities (the so-called undulators) will be producing highly brilliant flashes of X-ray laser light. Unique properties of such flashes open a perspective of rapid progress in research on structure of matter at the nano scale. European XFEL is expected to substantially impact medicine, energy production and storage, materials research, and many other R&D fields.

The design of the injector is strongly based on the one found in FLASH, DESY’s UV/soft X-ray free-electron laser, the prototype facility for the European XFEL (FLASH has been operated as an user facility since 2005). Several billion electrons are released from an electrode of caesium telluride when it is struck by an intense laser flash of ultraviolet light. The electrons form a bunch which is accelerated by RF electromagnetic waves and kept together by intense magnetic fields. The bunch is accelerated, first through a normal conducting cavity made of copper, then through a pair of superconducting accelerator cryomodules. The two latter devices are cooled down to ‑271°C by liquid helium to allow for highly efficient beam acceleration. These modules give the electron beam the required characteristics needed for producing X-ray flashes subsequently used to study matter at the atomic scale.

DESY, which is European XFEL’s main shareholder and close partner, is responsible for the construction and operation of the electron injector as well as the rest of the linear accelerator. Components for the injector are produced across Europe by 17 institutions participating in Eu-XFEL Accelerator Consortium. This includes work done by DESY, as well as in-kind contributions from other institutes located in France, Italy, Poland, Russia, Spain, Sweden, and Switzerland.

The injector will continue to go through rigorous testing while the rest of the linear accelerator is installed. The next major milestone will be to pass electrons through the entire accelerator to the European XFEL’s Osdorfer Born site approximately 2.1 km away from the starting point of the injector. This is expected in late 2016. It is also expected that the entire facility will reach fully operational status in 2017.

“The first electrons in the injector mark a major milestone for this ambitious discovery machine – my congratulations go to the physicists and engineers who have constructed and installed the components with great dedication” said Professor Helmut Dosch, chairman of the DESY Board of Directors. “And with more than half of the superconducting modules of the main accelerator tested and installed, I am sure that European XFEL accelerator commissioning procedures will start soon.”

Polish institutions have already delivered majority of the 28.8 million Euro worth Poland’s in-kind contribution to the European XFEL project. PAN Institute of Nu­clear Physics in Cracow has developed some dedicated software and procedures for testing superconducting microwave resonators to be used as components of li­near electron accelerator, as well as some complete modules of the accelerator. The tested subassemblies include: the complete modules (more than 60% of these tests have been concluded), sub-contracted resonators, 103 superconducting mag­nets (that are to focus and control electron beam within the accelerator). Faculty of Power and Mechanical Engineering at Wrocław University of Technology, the Krio­sys­tem company (Wrocław), and the KATES company (Olsztyn) have jointly design­ed and constructed a cryogenic line to transport liquid helium and two vertical cryostats for testing resonators at the liquid helium temperature. NCBJ has deve­loped and thoroughly tested 1,328 antennas whose task is to get rid harmful har­monics off electromagnetic field inside the resonators (the so-called HOM couplers), 664 diagnostic antennas to be deployed inside superconducting resonators (the so-called pick-up antennas) and 88 absorbers whose task is to eliminate propagation of higher harmonics. The HOM couplers have already been delivered to sub-contractors engaged in development of the Eu-XFEL laser (DESY, CEA Saclay). NCBJ’s contribution is worth about 3 million Euro.

Photon beams routed to experimental stands of the facility need shaping into some required time structure. Therefore some dedicated, automatically controlled equipment must be deployed within optical lines and on the stands itself. NCBJ is one of the sub-contractors hired to accomplish that task. 741,000 Euro worth contract for delivery of 100 modules that will couple control circuitry at experimental stands was reached between XFEL and NCBJ earlier this month. This will be the first in-kind contribution of Poland to another part of the project than its accelerator.

„Involvement into development of the facility means that Poland will be co-owner of the unique research infrastructure as well as of all discoveries and R&D results obtained with its help. Polish scientists will be given an opportunity to conduct structural studies using research equipment of an unprecedented resolution” – said Dr. Krzysztof Kurek, NCBJ Director General.

European XFEL has been classified by European Strategy Forum on Research Infrastructure as a major research facility in Europe. Once the facility becomes operational, European scientists will be among leading users of intense X-ray sources. The laser will help scientists to acquire 3D images of various nano-scale objects, in particular to visualize virus structural details (which should help to develop new medicines), to reveal molecular mechanisms at work inside living cells, to take video clips capable to reveal how chemical reactions proceed (e.g. forming/breaking chemical bonds), and to study processes running inside planets and/or stars. The facility will also make possible to modify properties of known materials and to develop quite new ones.

FEL lasers are a new generation of much brighter X-ray sources than those available just a few years ago. They are fed by linear electron accelerators. Radiation pulses generated by FEL lasers feature three very valuable properties:

• They are extremely bright, from 100 million up to 1 billion times brighter than synchrotron-generated radiation. Huge amount of light is emitted as a very narrow beam.
• They are extremely short, on the order of a few femtoseconds. 1 femtosecond (1 fs) is 1 billionth part of 1 microsecond (i.e. of 1 millionth part of a second). During such short time light can travel a distance shorter than 1/100 of a hair thickness.  
• The generated light is coherent (as in any laser), which means that waves propagating in various points of the beam are phase-correlated and mutually enhance themselves. Due to that latter property FEL-generated pulses are a much more useful tool for scientists than conventional (non-coherent) X-rays.