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.

The European XFEL GmbH (EuXFEL) is a FEL user facility based on a superconducting accelerator with high duty cycle. Three movable gap SASE Undulator Systems using hybrid NdFeB permanent magnet segments are in operation. We observed in a dedicated diagnostic undulator for radiation damage doses up to 4 kGy and 3% demagnetization effect during the commissioning phase. In this work we present characteristics of the absorbed radiation doses in undulators during photon beam delivery for users. Lower absorbed doses are measured since the start of user operation. While ramping up electron beam parameters and repetition rates, individual segments located at the downstream end of the SASE systems show persistent absorbed doses which are proportional to the transmitted charge. In addition, the dose per charge ratio shows photon energy dependence. Portable magnetic flux measurement systems allow in-situ tunnel assessment of undulator magnetic properties in order to estimate radiation dose limits for future user operation.

The European XFEL GmbH is a new X-ray FEL user facility and started lasing in 2017. Three movable gap SASE Undulator Systems based on hybrid NdFeB permanent magnet technology were built. Radiation damage due to machine operation affects the magnetic properties of the segments and the quality of the SASE process. Dosimeters monitor the absorbed doses in every undulator segment and each SASE system is equipped with a diagnostic undulator (DU). We report on the profile of the absorbed doses seen in the first year of the Undulator Systems operation. Magnetic field degradation higher than 3.5% in the DU is found and associated to absorbed doses up to 4.4 kGy. An initial limit of 55 Gy for the 5-m undulator segments is recommended based on the precise K-parameter determination for beam operation.

We report results from high-resolution studies of D5+ cluster ion collisions with low-energy electrons performed in a heavy ion storage ring. Absolute dissociative recombination (DR) and dissociative excitation (DE) cross sections were determined for the energy range from 0.0005 to 20 eV. The DR cross sections were exceedingly large at low energies, and DR resulted in efficient internal energy redistribution and pronounced fragmentation with two main product channels: D2+3D (0.62 ± 0.03) and 2D2+D (0.35 ± 0.01). The DR and DE cross sections were comparable in the energy range from 0.2 to 20 eV, which suggest that the two processes follow similar dynamics and are competing outcomes of the ion–electron interaction. A simple picture of the recombination process of D5+ which captures the essential physics is suggested.

Here we will briefly describe the commissioning of the Double ElectroStatic Ion Ring ExpEriment (DESIREE) facility at Stockholm University, Sweden. This device uses purely electrostatic focussing and deflection elements and allows ion beams of opposite charge to be confined under extreme high vacuum and cryogenic conditions in separate "rings" and then merged over a common straight section. This apparatus allows for studies of interactions between cations and anions at very low and well-defined centre-of-mass energies (down to a few meV) and at very low internal temperatures (down to a few K).

In this paper, we report results regarding how LiH2+ fragments as a result of a low-energy collision with an electron (dissociative recombination), a reaction that contains only elements and particles created during the very first phase of the universe. The collision-energy-dependent reaction rate and cross sections show detailed structures, more so than predicted by theory, suggesting significant rovibrational coupling in the ion and a complex reaction surface. From the structure of the molecule, the reaction predominantly results in the formation of Li + H-2. However, 23% of the reaction flux leads to more interesting products, with 17% producing Li + 2H and 6% producing LiH + H. These last two channels break the strongest molecular bond in the system and, in the case of the latter channel, form a significantly weaker ionic bond. Possible reasons behind this interesting behavior are discussed, together with the interaction between the available reaction channels.

We report on the ongoing commissioning of the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. Beams of atomic carbon anions (C-) and smaller carbon anion molecules (C-2(-), C-3(-), C-4(-) etc.) have been produced in a sputter ion source, accelerated to 10 keV or 20 keV, and stored successfully in the two electrostatic rings. The rings are enclosed in a common vacuum chamber cooled to below 13 Kelvin. The DESIREE facility allows for studies of internally relaxed single isolated atomic, molecular and cluster ions and for collision experiments between cat-and anions down to very low center-of-mass collision energies (meV scale). The total thermal load of the vacuum chamber at this temperature is measured to be 32 W. The decay rates of stored ion beams have two components: a non-exponential component caused by the space charge of the beam itself which dominates at early times and an exponential term from the neutralization of the beam in collisions with residual gas at later times. The residual gas limited storage lifetime of carbon anions in the symmetric ring is over seven minutes while the 1/e lifetime in the asymmetric ring is measured to be about 30 seconds. Although we aim to improve the storage in the second ring, the number of stored ions are now sufficient for many merged beams experiments with positive and negative ions requiring milliseconds to seconds ion storage.

We present product state distributions and quantum yields from the dissociative recombination reaction of O2 + in its electronic and vibrational ground states as a function of electron collision energy between 0 and 300 meV. The experiments have been performed in the heavy-ion storage ring, CRYRING, and use a cold hollow-cathode discharge source for the production of cold molecular oxygen ions. The branching fractions over the different dissociation limits show distinct oscillations while the resulting product quantum yields are largely independent of electron collision energy above 40 meV. The branching results are well reproduced assuming an isotropic dissociation process, in contrast with recent theoretical predictions. © 2005 American Institute of Physics . fDOI: 10.1063/1.1937388 g

In this proceedings I will describe the design of a new storage device currently under construction at Stockholm University, Sweden. This device uses purely electrostatic focussing and deflection elements and allows ion beams of opposite charge to be confined under extreme high vacuum and cryogenic conditions in separate "rings" and then merged over a common straight section. This Double ElectroStatic Ion Ring ExpEriment (DESIREE) apparatus allows for studies of interactions between cations and anions at low and well-defined centre-of-mass energies. I discuss the design of the DESIREE facility, highlighting some of the technical advantages of using purely electrostatic over magnetic elements, as well as the issues that have arisen during its development and construction. Finally, the advantages of this design are a boon to fundamental experimental studies and I finish by discussing an example of such potential research.

We describe the design of a novel type of storage device currently under construction at Stockholm University, Sweden, using purely electrostatic focussing and deflection elements, in which ion beams of opposite charges are confined under extreme high vacuum cryogenic conditions in separate "rings" and merged over a common straight section. The construction of this double electrostatic ion ring experiment uniquely allows for studies of interactions between cations and anions at low and well-defined internal temperatures and centre-of-mass collision energies down to about 10 K and 10 meV, respectively. Position sensitive multi-hit detector systems have been extensively tested and proven to work in cryogenic environments and these will be used to measure correlations between reaction products in, for example, electron-transfer processes. The technical advantages of using purely electrostatic ion storage devices over magnetic ones are many, but the most relevant are: electrostatic elements which are more compact and easier to construct; remanent fields, hysteresis, and eddy-currents, which are of concern in magnetic devices, are no longer relevant; and electrical fields required to control the orbit of the ions are not only much easier to create and control than the corresponding magnetic fields, they also set no upper mass limit on the ions that can be stored. These technical differences are a boon to new areas of fundamental experimental research, not only in atomic and molecular physics but also in the boundaries of these fields with chemistry and biology. For examples, studies of interactions with internally cold molecular ions will be particular useful for applications in astrophysics, while studies of solvated ionic clusters will be of relevance to aeronomy and biology.

Fundamental wavelength and phase-matching conditions in the XFEL undulator can be maintained during temperature changes with undulator gap adjustment in a temperature compensation scheme. Evaluation of a highprecision temperature measurement system suitable for the compensation scheme is presented together with a brief overview of an upgraded rotating coil system for fiducialization and characterization of the XFEL quadrupole magnets.

Dissociative recombination of the Zundel cation D(5)O(2)(+) almost exclusively produces D + 2 D(2)O with a maximum kinetic energy release of 5.1 eV. An imaging technique is used to investigate the distribution of the available reaction energy among these products. Analysis shows that as much as 4 eV can be stored internally by the molecular fragments, with a preference for producing highly excited molecular fragments, and that the deuteron shows a nonrandom distribution of kinetic energies. A possible mechanism and the implications for these observations are addressed.

A measurement system has been set up at the Manne Siegbahn Laboratory to measure the magnetic center of the European XFEL undulator quadrupoles. A rotating coil setup measures the center of the quadrupole magnetic field with respect to the rotational axis. The distance from the rotational axis to fiducials on the magnet is then measured with a coordinate measuring machine. The experimental setup and results from measurements on a test magnet are presented. The results show that the goal of measuring the quadrupole magnetic center better than 50 μm is feasible with this setup.

A rotating coil system together with a coordinate measuring machine have been set up at the Manne Siegbahn Laboratory in order to fiducialize the European XFEL undulator quadrupoles. The experimental setup is presented together with results from measurements on a test magnet which show that the goal to measure the quadrupole magnetic center better than 50 µm is achievable with this setup. The rotating coil was also used to measure the magnetic center stability of a prototype magnet made of Russian relay iron. The magnetic center stability is similar to previous results on prototype magnets made from different soft magnetic materials. The Russian relay iron is less expensive than the other materials and therefore preferred.

A rotating coil setup for magnetic field characterization and fiducialization of XFEL quadrupole magnets is presented. The instrument allows measurement of the relative position of the magnetic axis with accuracy better than 1 μm and measurement of weak magnetic error field components. Tests and evaluation based on a FLASH quadrupole magnet are presented together with a discussion for fiducialization of XFEL quadrupole magnets with accuracy better than 50 μm.

In this paper we report the results of a study on the dissociative recombination (DR) of the diacetylene cation, C4D2+, which has been carried out at the ion storage ring CRYRING in Stockholm, Sweden. The energy-dependent absolute DR cross-section as well as the branching fractions at ∼0eV collision energy were measured. The DR cross-section was best fitted using the expression σ(E)=(7.5±1.5)×10−16×E−(1.29±0.03)cm2 over the collision energy range 1–100meV. The thermal rate coefficient was deduced from the cross-section to be α(T)=(1.10±0.15)×10−6×(T/300)−(0.79±0.03)cm3/s. The reported branching fractions for C4D2+ agree with previous experiments on the DR of C4H2+ performed at the ASTRID storage ring in Aarhus, Denmark, and furthermore, indicate that the DR of C4D2+ possesses only two channels leading to the following products: C4D+D (75%) and C2D+C2D (25%).

A rotating coil setup for magnetic field characterization and fiducialization of XFEL quadrupole magnets is pre- sented. The instrument allows measurement of the rel- ative position of the magnetic axis with accuracy better than 1 μm and measurement of weak magnetic error field components. Tests and evaluation based on a FLASH quadrupole magnet are presented together with a discus- sion for fiducialization of XFEL quadrupole magnets with accuracy better than 50 μm.

At the end of the European XFEL the electron beam is separated from the photon beam and directed towards the beam dump with a bending magnet. This dipole magnet is designed to bend 10-25 GeV electrons by 1 ◦ /m and is 10 meter longin total. By integratingpermanentmagnetmaterial into a conventionalelectromagnet,this so-called hybrid magnet with a 1 T bias magnetic field consumes no power at the nominal energy of the XFEL, 17.5 GeV. The magnetic field can be increased or decreased by magnet coils to obtain 1 ◦ /m deflection for all energies between 10 and 25 GeV. Here a proposal for such a hybrid configuration is presented together with its characteristics.