13. February 2015

Successful start of the series production of the C-band accelerating structures for SwissFEL

A total of 104 C-band accelerating structures will be needed for SwissFEL. Each of these structures is about 2 m long and consists out of 113 copper cells that are manufactured with micrometer precision using ultra-precision diamond machining, which results in mirror-like surfaces. The main components are the couplers at the input and the output of the structure, and the copper disks. For both, couplers and disks, the series production was successfully launched at the end of 2014. Since then the Dutch company VDL and TEL Mechatronics in Trübbach, Switzerland, delivered already many sets of couplers and accelerating disks, respectively.

The copper parts are then further processed at PSI in a special installation in the AMI-workshop. This involves a cleaning of the parts, a heat treatment, and several brazing steps. The individual parts are then combined to a complete structure using a special stacking robot. After this, a brazing of the structure takes place in a big vacuum brazing furnace. The verification of the proper functioning of a completed structure then includes micrometer-precise surveying, vacuum leak tests, and a number of RF measurements in which the field profile and other RF properties are measured.

In the meanwhile, a total of 15 accelerating structures have been brazed at PSI, currently, every week a new structure is completed.

Facility: SwissFEL
Reference: Florian Löhl; florian.löhl@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

16. January 2015

Terahertz wavefront control for extremely bright THz bullet

M. Shalaby and C.P. Hauri “Demonstration of a low-frequency three-dimensional terahertz bullet with extreme brightness.” Nat. Commun. 6:5976 doi: 10.1038/ncomms6976 (2015).

The brightness of a light source defines its applicability to nonlinear phenomena in science. The SwissFEL laser group has now overcome one of the two principal technological hurdles to produce bright pulses in the Terahertz range (0.1-5 THz). Using a present-technology THz generation scheme based on optical rectification in organic crystal we were able to optimize the THz wavefront such that a spatio-temporal confinement of THz energy at its physical limits has become feasible – the least possible three-dimensional light volume of wavelength cubic. The gain of control on the THz wavefront is a technological breakthrough as it allows to reach the highest ever produced single-cycle Terahertz transients (up to 80 MV/cm, 25 Tesla) in a diffraction-limited spot size. While such field strength is of interest for many applications, the THz spot size might be too small for realistic pump-probe investigations. Therefore further developments are required to overcome the second hurdle being the increase of THz pulse energy. The SwissFEL laser team has proposed a novel approach which shall be explored in near future. The combination of both wavefront control and high THz pulse energy will open a new avenue in nonlinear THz optics and will be a unique tool for controlling properties in condensed matter by impulsive excitation.

Facility: SwissFEL
Reference: Christoph Hauri; christoph.hauri@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Record low emittance for compressed bunches at the SwissFEL Injector Test Facility

The emittance of the electron beam is crucial for Free-Electron Laser (FEL) facilities: it has a strong influence on the lasing performance and on the total length of the accelerator. The emittance of the whole bunch, called projected emittance, is a general indicator of the electron beam quality. However, the key beam parameter for FELs is the slice emittance, i.e. the emittance measured for individual slices along the bunch length. In practice, both slice and projected emittance need to be optimized. A procedure to measure and minimize the projected and slice emittance was developed and implemented at the SwissFEL Injector Test Facility, a 250 MeV accelerator that was in operation between 2010 and 2014 to demonstrate the feasibility of the SwissFEL design. A normalized slice emittance resolution of about 3 nm and a longitudinal resolution of about 13 fs were achieved, with measurement errors estimated to be below 5%. After performing a full optimization, a projected emittance of around 300 nm and a slice emittance below 200 nm were obtained for uncompressed beams with a charge of 200 pC. Moreover, after compressing the bunch from about 4 ps to about 0.5 ps, the emittance of the beam core was preserved. A second bunch compressor available at SwissFEL will compress the electron beam to its final length, e.g. to about 20 fs for a bunch charge of 200 pC. The measured core beam emittances at the SwissFEL Test Facility are consistent with numerical simulations and are well below the tight requirements of SwissFEL. At these bunch charges these slice emittances for both uncompressed and compressed bunches are, to the best of our knowledge, the lowest achieved so far for an electron linear accelerator.

Facility: SwissFEL
Reference: Eduard Prat; eduard.prat@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

A time-dependent order parameter for ultrafast photoinduced phase transitions

Published 3 August 2014 in Nature Materials DOI: 10.1038/nmat4046
The exploration of the interaction of structural and electronic degrees of freedom in strongly correlated electron systems on the femtosecond time scale is an emerging area of research. One goal of these studies is to advance our understanding of the underlying correlations, another to find ways to control the exciting properties of these materials on an ultrafast time scale. So far a general model is lacking that provides a quantitiative description of the correlations between the structural and electronic degrees of freedom. Here we investigate a perovskite-type manganite, a prototypical example of a strongly correlated electron system which exhibits properties such as colossal magnetoresistance and insulator-to-metal transitions that are intrinsically related to symmetry changes of the atomic lattice and to intriguing ordering patterns of the spins, orbitals and charges. The application of an ultrashort optical pulse melts the electronic order and launches a structural phase transition. The long-range electronic and atomic order during the transition is probed directly with time-resolved resonant x-ray diffraction. Although the actual change in crystal symmetry associated with this transition occurs over different time scales characteristic of the many electronic and vibrational coordinates of the system, we find that the dynamics of the phase transformation can be well described using a single time-dependent order parameter that drives the electronic phase transition as well as the coherent motion of the atomic lattice. The striking analogy of this formalism to Landau phae transition theory points to a possibly universal description of complex phase transitions in the time domain.
Facility: SwissFEL
Reference: Paul Beaud; paul.beaud@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

7 Å resolution in protein two-dimensional-crystal X-ray diffraction at Linac Coherent Light Source

B. Pedrini et al, Phil. Trans. R. Soc. B 2014 369, 20130500, published 9 June 2014, DOI:10.1098/rstb.2013.0500

Membrane proteins arranged as two-dimensional (2D) crystals in the lipid environment provide close-to-physiological structural information, which is essential for understanding the molecular mechanisms of protein function. Previously, X-ray diffraction from individual 2D crystals did not represent a suitable investigation tool because of radiation damage. That the recently available ultrashort pulses from X-ray Free Electron Lasers (X-FELs) provide a mean to outrun the damage is now well established for the 3D crystal case. This is now demonstrated also for the 2D crystal case, within the work of an international collaboration led by Matthias Frank from the Lavrence Livermore National Laboratory (CA, USA), to which scientists from PSI had the opportunity to participate and contribute. We report on the measurements performed in May 2013 at the Coherent Diffraction Imaging station of the Linac Coherent Light Source X-FEL, and using bacteriorhodopsin 2D crystals as samples. By merging data from about a dozen single crystal diffraction images, we unambiguously identified the diffraction peaks to a resolution of 7 Å, thus improving the observable resolution with respect to that achievable from a single pattern alone (see example in the Figure). On the one hand, this indicates that further improvements in resolution should be achievable by acquiring a larger dataset. will allow for reliable quantification of peak intensities, and in turn a corresponding increase of resolution. On the other hand, the presented results pave the way to further X-FEL studies on 2D crystals, which may include pump-probe experiments at subpicosecond time resolution.
Facility: SwissFEL
Reference: Bill Pedrini; bill.pedrini@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Lauch of the SwissFEL in Virtual Reality Model

On the 10.06.2014 the new SwissFEL in Virtual Reality Model was launched. The Model was realized in order to help society understand the importance of PSI's new large scale facility SwissFEL, which currently under construction.In 2016 the Swiss X-ray free electron laser will go into operation. The SwissFEL X-ray laser will generate extremely short, intense X-ray pulses. The unique properties of the SwissFEL will enable experiments to be carried out at a very high resolution in both time and space. This new facility will open the door to discoveries, in many areas of current research, which cannot be achieved using existing methods. The SwissFEL in a virtual reality model was realized with the help of the AGORA SNF funding project. SwissFEL in a virtual reality is a video game like device with whom SwissFEL researchers want to attract the general public, and especially groups usually less interested in research (i.e. people fancying videogames, entire families: parents in their thirties, with children between 8 and 15). The virtual model fosters communication of cutting edge research to the general public by explaining and guiding through the concept of Switzerland’s new cutting edge research facility through the new Virtual Reality Model in a playful way.
Facility: SwissFEL
Reference: Mirjam van Daalen; mirjam.vandaalen@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

First beam from the SwissFEL electron gun

6.06.2014 The new 3 GHz photocathode gun will provide the electron bunches for SwissFEL and has recently been installed in the SwissFEL injector test facility. There, it replaced the CTF2-gun 5, borrowed from CERN. The new gun is capable now of operation with 100Hz repetition frequency and a higher field on cathode and improved field symmetry. After RF conditioning of about 4 days, the gun reached the nominal acceleration gradient of 100 MV/m at an input power of about 17 MW and pulse-width of 1 microsecond. The gun incorporates the same type of copper cathode plugs, as the CTF2-gun and accelerates the electrons in 3 cells up to a kinetic energy of 6.6 MeV. Each cell has a pick-up for amplitude and phase monitoring. The first measurements of the electron beam on the spectrometer arm confirm the expected kinetic energy. Next weeks of test injector operation will be dedicated to gun commissioning and more detailed beam quality measurements.
Facility: SwissFEL
Reference: Lukas Stingelin; lukas.stingelin@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Investigating ultrafast magnetization dynamics with a table-top femtosecond XUV laser

The study of ultrafast dynamics initiated by a femtosecond laser pulse is a hot topic. Many questions, such as the angular momentum transfer during the laser-matter interaction are yet unanswered which calls for advanced metrology. In order to investigate ultrafast transient dynamics in magnetic materials we have now implemented a new diagnostic scheme at our extreme UV high-harmonic (HHG) beamline which is based on the Transverse Magneto-Optic Kerr effect (T-MOKE). Thanks to its coherent, multi-color emission our table-top XUV scheme allows synchronous tracking of the magnetization dynamics of multiple elements at femtosecond resolution. This opens exciting opportunities for time-resolved studies particularly in alloys (e.g. permalloy (20% Fe/80% Ni) and more complex materials to gain a deeper understanding of the dynamics occurring at the the onset of the laser-matter interaction. Presently, our scheme allows investigations at the M absorption edge of ferromagnetic materials (40-70 eV) and will be extended to higher photon energies in near future. Our scheme complements the experimental opportunities given at Free Electron Lasers, where element-selective investigations have not been demonstrated so far.
Facility: SwissFEL
Reference: Christoph Hauri; christoph.hauri@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Large European R&D project holds its third annual meeting on the epn campus in Grenoble/France

Large research infrastructures are built on making the latest in technology for use in scientific experiments available to scientists. This often requires joint R&D efforts, and the CRISP project is bringing together eleven main players from across Europe to address four key technology areas for the big science of tomorrow. CRISP was launched in October 2011; the third annual meeting was the occasion to review the current status of the project, present some of the major accomplishments, and to coordinate the work for the last months of the project.

CRISP - the Cluster of Research Infrastructures for Synergies in Physics (http://www.crisp-fp7.eu) - is a 3-year project partly funded by the European Commission with 12 million Euros from the 7th Framework Programme. CRISP comes in four flavours of technological R&D: particle accelerators; large-scale physics instruments and experiments; detectors and data acquisition technologies; IT and data management systems.

Progress in accelerator technology is essential to provide research infrastructures with the best possible sources of Xrays, ions and neutrons, and to tackle tomorrow’s challenges in nuclear and high-energy physics. Joint developments for novel types of large-scale physics experiments and their related instrumentation will also create new scientific opportunities, across many other fields of science. New initiatives and approaches are required to cope with the everincreasing flow of data from large experiments, and a joint effort will establish the technological base for adequate platforms for the processing and storage of, and access to these data.

Within the CRISP project, the eleven participating research entities exchange know-how and combine their complementary expertise, ensuring cost-efficient and coherent development of new technologies. Such synergies are crucial to respond to a rapidly evolving and internationally mobile community of scientists using these large-scale research facilities. As major players in cutting-edge science, they also contribute to the technological progress needed for tackling big societal challenges in health, environment, sustainable energy, transport and communication.

The eleven partners of the CRISP Project are listed on the roadmap of the European Strategy Forum on Research Infrastructures (ESFRI). They are under construction (ELI, ESS, EuroFEL, European XFEL, ILC-HiGrade and SKA), or research infrastructures in operation undergoing an important upgrade (ESRF, GSI-FAIR, ILL, SLHC@CERN and GANIL-SPIRAL2).

The third Annual Meeting was jointly hosted from 2 to 4 June 2014 by the ESRF and the ILL. It took place on the epn campus in Grenoble, and attracted more than 100 participants. The meeting started with parallel topic meetings on Monday morning, before the opening of the plenary meeting at 14h, featuring three keynote lectures. John Womersley, the current chair of the European Strategy Forum on Research Infrastructures (ESFRI), explained the role of ESFRI and its priorities within the new framework program Horizon 2020; Alex C. Mueller presented the current status and perspectives for the SPIRAL2 and FAIR facilities; and Lyn Evans, the project leader of the Large Hadron Collider, offered fascinating insights from the design and the construction of the LHC to the discovery of the Higgs boson. Following short status reports from the eleven participating research infrastructures, the meeting continued with a poster session and a buffet dinner in the recently inaugurated Science Building. The Tuesday session started with five highlight talks from the CRISP project, covering subjects from accelerator components diagnostics to federated identity management. These were followed by the status reports from the four topic leaders, and a guided tour to the ESRF and ILL facilities. The meeting left ample time for exchange of ideas, and lively discussions continued during the dinner which took place in the Chateau de la Commanderie in Eybens.
Facility: CRISP 3rd annual Meeting
Reference: Mirjam van Daalen; mirjam.vandaalen@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Coherent femtosecond radiation up to 300 eV

State of the art table-top high-order harmonic (HHG) sources driven by an intense femtosecond are routinely used to produce coherent soft x-ray pulses up to a photon energy of 100 eV. It is clear that many applications would benefit from higher photon energies, such as seeding a free electron laser, imaging of biological tissue in the water window (285 eV-530 eV) or the investigation of ultrafast magnetization dynamics in transition metals and rare earth elements with absorption edges in the range >100 eV. Motivated by such applications, the SwissFEL laser group has now extended the maximum photon energy from a table-top laser-driven source from 100 eV up to 300 eV (4 nm), by altering the driving laser wavelength from 0.8 m to 1.9 m. This significant shift in the cut-off energy becomes possible since the maximum achievable HHG photon energy scales with the square of the driving laser wavelength (see Figure). Even though the present photon flux is still quite low, this development is considered a first important step towards seeding the future soft x-ray branch at SwissFEL. Seeding an FEL helps to improve its temporal coherence and would provide an excellent scheme for x-ray pump and laser probe at intrincially low temporal jitter. Our future developments aim therefore at improving the HHG photon flux by exploring novel phase-matching schemes. Our present HHG source will also provide an excellent test bed for some pre-trigger experiments later on performed at the SwissFEL soft x-ray beamline.
Facility: SwissFEL
Reference: Christoph Hauri; christoph.hauri@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland


The workshop of the PSI engineering department (AMI) recently completed the manufacturing of the high brightness electron source that will drive SwissFEL. The first characterization of the 2.5 cells RF photo cathode is in excellent agreement with the design values without applying a post-manufacturing tuning. This confirms the quality of design [1], engineering and manufacturing process performed at PSI [1]. After completing the fine characterization of the cavity and the calibration of the pick-ups, in April 2014, the RF-gun will be integrated into the SwissFEL Injector Test Facility, where the gun performances will be tested at high power and with electron beam.

[1] J.-Y.- Raguin et al, Proceedings of LINAC2012, Tel-Aviv, Israel
Facility: SwissFEL
Reference: Hans Rudolf Fitze; hansruedi.fitze@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

First lasing in SwissFEL test facility

On the 15th of January 2014, first lasing was achieved in the SwissFEL injector test facility. This is a great success on the way towards SwissFEL, the future hard x-ray free-electron laser that is currently under construction at PSI. It proves the successful functioning of many key components together in a larger system as required for SwissFEL. Furthermore, this is the very first operation of a free-electron laser in Switzerland. Since 2010, PSI has been operating a test facility to study and optimize the electron source for SwissFEL. Over the last years, the test facility was advanced to one of the most brilliant electron sources in the world, and during the last shutdown end of 2013, a first undulator - a highly precise periodic array of magnets - was installed in the facility. This innovative type of undulator is an in-vacuum design with a very small period length of only 15 mm, that was specifically developed for SwissFEL. During the very first beam time after the installation of the undulator, the electron beam could be successfully tuned to pass the undulator with low losses - this is very important to prevent radiation damage to the sensitive 1060 permanent magnets of the undulator. The electrons generate spontaneous radiation when passing the undulator, and this radiation was detected with scintillator screen monitors. In a next step, the electron beam was strongly compressed in a bunch compressor chicane to generate a very large charge density, which is required for the FEL process. This initiated the free-electron lasing process, leading to an exponential increase of the emitted radiation along the undulator. An electron beam with an energy of 220 MeV and a bunch charge of 200 pC was used in that process, and first lasing was detected at a wavelength of around 80 nm. By adjusting the gap of the undulator, the wavelength of the emitted laser light could be tuned over one octave from around 45 to 90 nm
Facility: SwissFEL
Reference: Hans Braun; hans.braun@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Installation of SwissFEL Undulator Prototype in the Injector Test facility

On December 5th, the 17 tons SwissFEL undulator prototype (In-vacuum Undulator U15) has been successfully moved from the Undulator lab (SLS) to the SwissFEL Injector Test Facility (SITF). The commissioning of the U15 prototype with electron beam is an important step to validate the U15 design and also to detect possible improvements before full series production. At first, the alignment procedure of the U15 segment with the electron beam will be tested. Later, twelve such U15 segments will have to be precisely aligned on a straight line in SwissFEL. Another important step at SITF, will be the detection of free electron laser amplification at 70 nm. Indeed, simulations have shown that with the electron beam parameters within reach at SITF, it should be possible to see the beginning of the SASE (self-amplified spontaneous emission) amplification.
Facility: SwissFEL
Reference: Romain Ganter; romain.ganter@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

New device tested for SwissFEL: Photon Arrival and Length Monitor (PALM).

The accurate measurement of the time between a pump laser pulse and a FEL probe pulse is vital to the success of the future SwissFEL facility, which plans to use pump-probe science as a cornerstone of its activities. This measurement, along with the measurement of the time-profile of the FEL pulse, is the goal of the new device designed and tested by the Photonics group at SwissFEL called the Photon Arrival and Length Monitor (PALM). Using a technique called THz-streaking, the device looks at electrons photoionized by FEL radiation and accelerated by an oscillating THz field generated by a laser to determine when during the field’s oscillation the electron was generated from a gas. The accuracy of this type of experiment in laboratory environments has been measured to several femtoseconds, and the group at SwissFEL photonics intends to replicate this feat. The first experiments have been conducted at the Aramis laser hutch in WLHA, using an high-harmonic generation (HHG) laser source to simulate the FEL beam, and have shown the viability of the design, measuring an arrival time accuracy between a HHG laser and THz beam to 8 fs RMS. The preliminary experiments looked at electrons with kinetic energies between 22 and 45 eV, and noted a maximum streak, or gain in their energy as a function of the delay between the HHG and THz beams, of about 2 eV.
The future developments for the PALM lay in optimizing the device to be able to cope with large jitters between the FEL pulse and the pump laser pulse, as well as the integration of the PALM with other methods that may, eventually, yield sub-femtosecond accuracy in both arrival time and pulse length measurements.
Facility: SwissFEL
Reference: Pavle Juranic; pavle.juranic@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

52 MV/m in C-band structure

This summer, the first 2 m long C-band accelerating structure for SwissFEL was installed in the high power test stand at PSI. The goal was to verify that the accelerating structure can handle the high accelerating fields of around 28 MV/m that are needed for SwissFEL. At such high accelerating fields, sporadic break-downs are unavoidable, and a second goal was to confirm that the number of break downs is at a level that is acceptable for SwissFEL. For this first accelerating structure, both of these investigations led to excellent results. An accelerating gradient of up to 52 MV/m - almost twice the nominal field - was reached, and this gradient was not limited by the structure itself but by the available radiation shielding. At the nominal accelerating field, the measured break-down rate was significantly lower than what is required for SwissFEL. Currently, a second accelerating structure is installed in the test stand, and preparations are ongoing to setup a complete accelerating module consisting out of four structures.
Facility: SwissFEL
Reference: Florian Löhl; florian.loehl@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

First beam: XUV laser meets Terahertz laser

Two new coherent photon sources, combined on a single laser table, have been built by the SwissFEL laser group and are operated successfully since several weeks by now. While the first type of laser delivers intense radiation in the Terahertz region at around 0.3 THz (i.e. 1 mm wavelength), the second laser source is a table-top, laser-driven XUV source based on high-order harmonic generation. It delivers photon energies up to 120 eV (i.e. 10 nm wavelength) in fully coherent XUV bursts of a few tens of femtosecond or even attosecond duration. The availability of these two complementary laser sources in one common lab opens up new opportunities. Scientifically, it allows for THz pump/XUV probe experiments at extremely short time-scales, such as element-specific investigations of ultrafast magnetization processes in compounds, or to drive coherent Zeeman spin precessions initiated by a strong THz stimulus. On the other hand, the XUV-THz laser assembly offers a realistic test bed for future SwissFEL temporal diagnostic equipment. Even though the photon flux will be orders of magnitude larger at SwissFEL, the lab-scale laser facility is a cheap and efficient way to explore the feasibility of advanced time-arrival schemes, such as the Terahertz streak camera currently developed by Dr. Juranic. Indeed, this timing tool has recently been successfully commissioned and debugged at our HHG/THz beamline and will next be tested on the hard x-ray FEL in Japan. Ongoing developments are aiming to extend the HHG photon energy towards the keV range with the vision to explore ultrafast magnetization dynamics by the T-MOKE technique at the L-absorption edge of magnetic materials like Cobalt. Such experiments could be pre-cursers for investigations at the future SwissFEL soft x-ray beamline where higher photon flux will be available.
Facility: SwissFEL
Reference: Christoph Hauri; christoph.hauri@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

First measurement campaign of the U15

The first measurement campaign of the U15 (the undulator prototype for the SwissFEL project) shows that electron trajectory straightness (measured with a dedicated Hall Probe bench) can be optimized beyond the micrometer level over the full operational range. Such trajectory straightness (about 10 times better than requirements) is attained thanks to an automatized shimming procedure based on individual pole height adjustment. The stability over the operational gap range is achieved thanks to the novel undulator support structure designed at PSI and to the status of the art manufacturing services of the Swiss industrial partner, Max Daetwyler AG.
Facility: SwissFEL
Reference: Romain Ganter; romain.ganter@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Magnetisation controlled at picosecond intervals

A terahertz laser developed at the Paul Scherrer Institute makes it possible to control a material’s magnetisation at a timescale of picoseconds (0.000 000 000 001 seconds). In their experiment, the researchers shone extremely short light pulses from the laser onto a magnetic material, where the magnetic moments – “elementary magnets” – were all aligned in parallel. The light pulse’s magnetic field was able to deflect the magnetic moments from their idle state in such a way that they exactly followed the change of the laser’s magnetic field with only a minor delay. The terahertz laser used in the experiment is one of the strongest of its kind in the world. One special feature is the fact that it is phase-stable, which enables the exact change in the electrical and magnetic field within the individual pulses to be defined reliably for each laser pulse. As the majority of data is stored magnetically these days, the possibility to quickly change a material’s magnetisation is crucial for new, rapid storage systems. The researchers report on their results in the journal Nature Photonics. Read more
Facility: SwissFEL
Reference: Christoph Hauri; christoph.hauri@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Last high power RF plant of the SwissFEL Injector Test Facility

End of May 2013 the last high power RF plant of the SwissFEL Injector Test facility became operational. The plant consist in a X-band (12 GHz) high power amplifier capable of producing RF pulses up to 50 MW power, feeding a 70 cm long accelerating cavity. This cavity operates at the fourth harmonic of the basic RF system used for accelerating the beam up to 250 MeV. Operated in decelerating mode, the X-band system allows removing the correlated non-linearity of the energy distribution induced by the RF curvature in the acceleration stages. This feature is essential to achieve an efficient compression of the electron bunches without degrading the beam properties. The figure illustrates the effect of the cavity. In the first picture, with X-band system off, the curvature induced by the RF with on crest acceleration is wisible, while in the second the curvature is completely removed by the harmonic system.
Facility: SwissFEL Injector Test Facility
Reference: Marco Pedrozzi; marco.pedrozzi@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

First C-band accelerating structure

In May 2013, the first 2 m long accelerating structure for the linear accelerator of SwissFEL was finalized at PSI. In total, 104 of these accelerating structures will be needed to accelerate the ultra-bright electron beam of SwissFEL to an energy of 5.8 billion electron-volt. By coupling a high-power 5.7 GHz RF pulse into the structure, an accelerating field of around 30 million volts per meter is generated inside of the structure. While the concept is based on a similar technology used at the x-ray free-electron laser SACLA in Japan, an entirely new design was developed at PSI, which will allow SwissFEL to operate with a significantly better power efficiency. Later this month, the structure will be installed in the C-band test stand to evaluate its performance under high power operation.
Facility: SwissFEL
Reference: Florian Löhl; florian.loehl@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

X-ray Laser: A novel tool for structural studies of nano-particles

Development of analysis method for X-ray laser scattering data.

Prominent among the planned applications of X-ray free electron laser facilities, such as the future SwissFEL at the Paul Scherrer Institute, PSI, are structural studies of complex nano-particles, down to the scale of individual bio-molecules. A major challenge for such investigations is the mathematical reconstruction of the particle form from the measured scattering data. The experiment consists of exposing the nano-particles to the X-ray laser pulses and of registering the resulting scattered rays. To guarantee sufficient statistical accuracy, many repeated exposures are required – each one on a different collection of identical, but randomly-oriented particles. Researchers at PSI have now demonstrated an optimized mathematical procedure for treating such data, which yields a dramatically improved single-particle structural resolution. The procedure was successfully tested at the Swiss Light Source synchrotron at PSI, with custom-fabricated, two-dimensional nano-structures. With the inclusion of some additional information, such as the particle symmetry, the method can be extended to real three-dimensional objects. The researchers report their results on-line in the current issue of Nature Communications. Read more
Facility: SwissFEL
Reference: Bill Pedrini; bill.pedrini@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

An intense Terahertz source for SwissFEL

Terahertz radiation (0.1-10 THz), located between the optical and radio frequency range, is suited to explore fundamental physical phenomena and to drive novel applications in condensed matter physics, biology, surface chemistry and others. Ultrashort and intense Terahertz pulses are of particular interest in view of the future hard x-ray free electron laser at PSI, since a series of resonant modes (magnons, phonons, electromagnons) can be coherently excited by THz and tracked by the femtosecond x-ray pulses. A high-field Terahertz transient provide a novel tool to control and investigate collective motions since it can be understood as "cold" stimulus: indeed the photon energy in the THz range is not more than a few meV, and therefore orders of magnitudes lower than the equivalent photon of a conventional laser (e.g. Ti:sapphire laser h=1.6 eV). While the latter heats electronic system significantly, the terahertz driving field excites only the THz sensitive port while leaving other degrees of freedom unexcited. Read more
Facility: SwissFEL
Reference: Christoph Hauri; christoph.hauri@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Record low emittance at the SwissFEL Injector Test Facility

The SwissFEL injector test facility at PSI is the principal test bed and demonstration plant for the SwissFEL project. Significant progress has been achieved in the past few months, during which the injector settings were systematically optimized for maximum brightness of the electron beam (low emittance at high beam current).

The result of this optimization is a stable working point for uncompressed electron bunches, which ensures beam transport with minimal emittance dilution. Once the influence of the accelerator itself on the beam emittance is kept at a minimum, subtle effects of the laser generating the electrons at the cathode (via the photo-electric effect) become accessible to beam optics measurements. In this way it was possible, for instance, to demonstrate the effect of the laser photon energy (or wavelength) on the beam emittance. During these studies extremely small emittances were measured, in particular for low bunch charges, where the adverse effects of Coulomb repulsion (space charge) are also smallest. But even at the nominal SwissFEL working point of 200 pC charge and with the standard laser wavelength of 260 nm, which ensures high electron yield, record low emittances well below the SwissFEL requirements have been achieved. At these conditions, global (projected) emittances below 0.35 mm mrad are now obtained routinely, with best values around 0.30 mm mrad. The more relevant slice emittance, i.e. the emittance measured for individual slices along the bunch length, which represents a key beam parameter for free-electron lasers, is typically below 0.20 mm mrad, with a record value of 0.18 mm mrad (see image).

These promising results were obtained with still uncompressed electron bunches. To reach the high peak currents necessary to drive a free-electron laser, longitudinal bunch compression is essential. The study of compressed electron bunches at the SwissFEL injector test facility is planned for 2013, when a linearizing harmonic cavity will be installed. The new cavity will allow for a more uniform compression of the bunch in the magnetic chicane (the so-called bunch compressor).
Facility: SwissFEL Injector Test Facility
Reference: Thomas Schietinger; thomas.schietinger@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

New opportunities for coherently exciting magnetic materials

The ability to manipulate matter on ultra-short time scales offers potential breakthroughs in future device technologies as well as a better understanding of fundamental material properties. For this purpose, it is of immense importance to be able to selectively drive excitations of interest. This has recently been demonstrated by team of researchers from PSI, the ETH, Stanford (SLAC) and Berkley with an experiment (performed in July 2012) at the x-ray free electron laser LCLS. They showed that a coherent electromagnon can be excited with a short THz pulse in multiferroic TbMnO3. Electromagnons are hybrid excitations of a magnon and a phonon that couple polarization with magnetism in multiferroic materials. The material was studied by time dependent resonant magnetic soft x-ray diffraction (see figure 1). A detailed analysis of the immense amount of data acquired in the experiment will verify if the excitation is indeed an electromagnon and give a quantitative estimate of the motion of spins involved. This experiment demonstrates that it is now feasible to coherently control magnetic moments. This is due to newly available methods of creating short, intense THz pulses, and to the availability of x-ray free electron lasers that allow us to study such responses of the material in real time.
Facility: LCLS at SLAC in Stanford
Reference: U. Staub; urs.staub@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
S. Johnson; johnsons@ethz.ch; ETH Zürich Institute for Quantum Electronics

Progress at the SwissFEL Injector

From 2011 to 2012 major progress was made at the SwissFEL Injector test facility. The installation of the magnetic bunch compression chicane was completed in July 2011. The following months were dedicated to the consolidation of the S-band RF system, the integration of the longitudinal diagnostics at the bunch compressor and the amelioration of the stability of the photo-cathode laser system.
In early April 2012 beam development studies started again, for the first time with all RF accelerating cavities in operation at the same time. The nominal beam energy of 250 MeV was reached for the first time on April 11. Within a couple of weeks of operation at the SwissFEL nominal charge of 200 pC it was possible to demonstrate transverse beam quality fulfilling the FEL requirements for uncompressed beam thus reaching an important milestone. The smallest measured values for projected and slice emittance at the beam core are 0.37 and 0.25 mm mrad, respectively.
The first compression experiments using the bunch compression chicane resulted in a compression factor of 18 corresponding to a reduction of the rms bunch length from 3.6 to 0.2 ps. To achieve the nominal bunch parameters after compression a harmonic (X-band) RF cavity is foreseen to be installed upstream of the bunch compressor later in 2012. This additional cavity will compensate the electron bunch curvature in longitudinal phase space introduced by the RF non-linearity in the preceding accelerating cavities. This system will be the last key component required to complete the SwissFEL Injector test facility.
Facility: SwissFEL Injector Test Facility
Reference: M. Pedrozzi; marco.pedrozzi@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

PSI scientists perform the worlds first hard X-FEL user experiment at SLAC

In October 2010, the commissioning phase of the X-Ray Pump-Probe experimental station at the Stanford LCLS source was finished. The very first user experiment in the hard x-ray range was carried out by a group of scientists from SLAC, the European XFEL and PSI under the lead of Christian David (PSI) more information
Facility: LCLS at SLAC in Stanford
Reference: Christian David; christian.david@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

FEL Prize Winners of 2009 and 2010 work together at the SwissFEL Injector

Last years FEL Prize winners Paul Emma and David Dowell, work together with this years FEL prize winner, Sven Reiche at the SwissFEL injector test facility. The FEL Committee awards one prize each year to a person or people whose work has advanced the field of free-electron laser science. Our colleagues from LCLS received the first FEL prize that was given to an operating machine, i.e. LCLS (world's first operating XFEL). Sven Reiche received his prize for more theoretical work on FEL simulation codes. These joint forces of outstanding scientists, with expertise's in different fields, working on the SwissFEL injector, shows once again the high international importance of the SwissFEL project as well as the strong global network SwissFEL is part of.
Facility: SwissFEL Injector Test Facility
Reference: Hans Braun; hans.braun@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

A prestigious FEL award for an outstanding scientist at the Paul Scherrer Institute

At the 32nd International Free Electron Laser Conference in Malmö, Sweden, the Prize Committee decided to award the prestigious 2010 FEL prize to Dr. Sven Reiche for “his outstanding contributions to the advancement of the field of Free-Electron Laser science and technology”.

The FEL simulation code, GENESIS 1.3 developed by Dr. Sven Reiche, is used as design tool world wide, and the anticipated performances of new projects have been very successfully benchmarked with experimental results in the most advanced FEL facilities. He contributed to all major FEL projects, influencing the machine layouts according to user’s expectances, as well as anticipating possible operational modes that in the near future could enlarge the experimental perspectives of the X-ray FELs. Today at the Paul Scherrer Institute, Dr. Reiche plays an essential role in the SwissFEL project, leading the FEL line design and coordinating the accelerator beam dynamic activities. Remarkable as well are his contributions to the SwissFEL science case and to the implementation of new schemes for the experimental lines. We congratulate Sven for the prestigious award as recognition of his outstanding career.

The SwissFEL Project Management Team
Reference: S.Reiche; sven.reiche@psi.ch
Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

First beam at the SwissFEL Injector Test Facility

The technical development of the project has reached another milestone: In the SwissFEL injector test facility the first electron beam from the gun has been extracted and accelerated to 5 MeV on the 12th of March 2010. The characterization of the beam, improvements on their quality and the implementation of the diagnostic are the short term goals. We express our thanks all to the groups that worked hard for these achievements, as well as for the installation of the whole facility.
Facility: SwissFEL Injector Test Facility
Reference: M. Pedrozzi; marco.pedrozzi@psi.ch; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

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Dr. Mirjam van Daalen
Science Officer SwissFEL

+41 56 310 56 74

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