Accelerators 2017

Dear Colleagues and Friends of DESY, The year 2017 was a year of truly outstanding achievements at DESY as one of the world’s leading accelerator centres, especially regarding the European XFEL X-ray laser project. The beam commissioning of the European XFEL accelerator complex, the demonstration of first hard X-ray free-electron laser (FEL) radiation and the provision of first photon beams to users are the most prominent highlights of this remarkably successful period. In 2016, the completion of the European XFEL accelerator construction, the beginning of its technical commissioning and the successful beam commissioning of the injector had laid the foundation for the progress that was to follow in 2017. The sections of the superconducting linear accelerator were successively put into operation, and by April 2017, most of the radio frequency (RF) sections were active and the electron beam had reached the beam dump after the accelerator tunnel. Transport of the beam through the first undulator line (SASE1) was then quickly established, and after steering optimisation, a clear FEL radiation signal was observed for the first time on 2 May. The first lasing was an unplanned, but most welcome timely match with the concluding meeting of the DESY-led Accelerator Consortium on 4 May at DESY. At that event, the 17 institutes involved in the construction of the accelerator complex reviewed their joint work of the past seven years and celebrated the completion of their mission. All involved DESY staff members together with their colleagues from the collaborating institutes could look with pride and satisfaction on the achievements in one of the largest and most challenging projects in the history of DESY. During the following months, the beam parameters were further improved, and a photon beam wavelength of 0.13 nm and a pulse energy of up to about 1 mJ were reached, both already close to the European XFEL specification. An electron beam energy of 14.9 GeV was achieved with two RF stations still inactive, which are to be commissioned in 2018. Ramping up the beam intensity has to be done with care to minimise radiation damage risk, and in this initial phase, FEL operation was limited to 30 bunches per accelerator pulse. In machine studies, however, operation with 300 bunches (3 kHz average bunch rate) was already successfully demonstrated. The rapid progress of the beam commissioning was achieved thanks to reliable and well-performing subsystems, including diagnostics and controls, and thanks to the strongly committed and competent operations team. Last but not least, the very open and constructive cooperation between the DESY XFEL team and the colleagues from European XFEL has been – and will continue to be – a crucial component for the achievements at this new world-leading facility. Much of the success story of the European XFEL accelerator is based on past developments for and experience with the FLASH soft X-ray FEL facility at DESY. FLASH itself had again an excellent year of user operation with high availability and performance. By now, the parallel operation of the two undulator beamlines FLASH1 and FLASH2 has become routine. A refurbishment and improvement programme, supported by additional investment funding, started in 2017, and a few items on the to-do list were already completed. Operation with short bunches (down to single-spike photon pulses) has been further developed and is now being made available to users. The sFLASH seeding experiment produced several new results, including the extraction of detailed and otherwise hardly accessible properties of the electrons using time-resolved measurements with the LOLA deflecting structure, which enables a precise characterisation of the seeded FEL pulse properties. In the course of the DESY strategy process, the mid- and longer-term perspectives for improvements and upgrades at FLASH are being developed and willbe further sharpened, taking into account the scientific priorities and boundary conditions regarding available resources. The PETRA III synchrotron radiation source had a very good operation year, with the highest figure for the availability (98%) since the facility served its first users in 2010. The achievement demonstrates that previous improvements in component and subsystem reliability have paid off. Further efforts are under way to systematically address the reliability challenge and stabilise the availability at such an internationally competitive high level. Further progress was obtained in the design studies for an upgrade of PETRA towards an ultralow-emittance storage ring (PETRA IV). The challenging task of conceiving a layout with an emittance of <20 pm rad at 6 GeV beam energy and still sufficient dynamic aperture is being addressed using different lattice design approaches. A final design decision on which the further detailed technical layout will be based will be taken after careful investigation and comparison of the different options and is foreseen for the end of 2018 or early 2019. Studies of an improved version of the DESY II synchrotron (DESY IV) have also started, and first preliminary results indicate that the emittance could be reduced by at least one order of magnitude with respect to the present machine, an improvement required for efficient electron injection into the new PETRA IV ring. In parallel to the lattice design and beam dynamics studies, first investigations of magnet, girder, vacuum and RF system concepts were also launched in the technical groups of the Accelerator Division. Novel accelerator concepts have become a rapidly growing field at DESY. The LUX experiment led by the University of Hamburg demonstrated undulator radiation from an electron beam with an energy of several hundred MeV produced in alaser-driven plasma wakefield. Moreover, a continuous 24 h run showed that the accelerated beam had 98% uptime and was reproducible in energy to a few percent, an important step towards usable beams from plasma accelerators. Much progress was obtained with the installation of the electronbeam- driven plasma wakefield experiment FLASHforward, and a first electron beam was injected into the FLASHforward beamline in the FLASH2 tunnel. At the PITZ photoinjector test facility at DESY in Zeuthen, self-modulation experiments of the electron bunch in a plasma cell were continued. The EU-funded multi-GeV laser plasma wakefield acceleration design study EuPRAXIA, coordinated at DESY, picked up momentum. Preparations and necessary refurbishments for the construction of the SINBAD accelerator R&D infrastructure in the former DORIS building at DESY were completed, and the first components for the ARES linear accelerator were ordered. The research perspectives on plasma acceleration will be strongly boosted by the ATHENA project, for which the final funding decision within the Helmholtz Association is expected for the first half of 2018. The SINBAD infrastructure also integrates the EU-funded AXSIS experiment for THzdriven acceleration as well as the activities at DESY and the University of Hamburg within the ACHIP collaboration for laser-driven microstructure acceleration funded by the Gordon and Betty Moore Foundation.