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  • richardmitnick 8:47 pm on May 26, 2017 Permalink | Reply
    Tags: , , DESY Flash, , Profiling FLASH electron bunches on a femtosecond scale,   

    From DESY: “Profiling FLASH electron bunches on a femtosecond scale” 

    DESY
    DESY

    2017/05/26
    No writer credit found

    Scientists use external seeding to monitor few-femtosecond slices of ultra-relativistic electron bunches.

    The success of FELs, having a transformative impact on science with X-rays, relies on the capability of analysing and controlling ultra-relativistic electron beams on femtosecond timescales. One major challenge is to extract tomographic electron slice parameters for each bunch instead of projected electron beam properties. A team of scientists has developed an elegant method to derive the slice emittance from snapshots of electron bunches with femtosecond resolution. Mapping of electron slice parameters and seeded FEL pulse profiles is an important ingredient for both, today’s large scale facilities and future compact table-top FELs and creates new opportunities for tailored photon beam applications. The project team headed by Jörg Rossbach from the University of Hamburg, DESY photon scientist Tim Laarmann and DESY accelerator physicist Jörn Bödewadt, reports its work in the journal Scientific Reports.

    1
    View into the seeding area of FLASH (photo: Dirk Nölle).

    DESY/FLASH

    Since 2005, DESY´s free-electron laser FLASH in Hamburg delivers ultra-short high-brilliance photon pulses to a wide range of scientific users. The light pulses are generated by electron bunches that are accelerated to a velocity close to the speed of light. These bunches have lengths of less than 100 μm, the diameter of a human hair. After acceleration, they traverse a series of magnets with alternating polarities, the undulator, and emit bright, soft X-ray light. While a synchrotron light source like PETRA III works very similar, a free-electron laser makes use of a further phenomenon: “During the emission process, different parts of the electron bunch organize themselves into thin microbunches with a distance of the wavelength of the emitted light,” explains principal author and PhD student Tim Plath. “Several parts of the bunch undergo this process with slightly different wavelengths and phases leading to a spiky structure of the spectrum. It is in the nature of this spontaneous amplification process that the properties are slightly different from shot to shot. This process is called self-amplified spontaneous emission (SASE) and is routinely used at many FEL facilities”.

    3
    Experimental setup of the seeding experiment at FLASH. From left: The beam comes from the linear accelerator and is overlapped with an external seed laser. In the modulator the laser imprints an energy modulation on the electron bunch that gets transformed to a density modulation by the bunching chicane. The formed microbunches can then coherently emit radiation in the radiator. The experimental setup is followed by a diagnostic for the photons and the rf deflector that can diagnose the electron bunch distribution (picture: Tim Plath, UHH/DESY).

    See the full article here .

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    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
  • richardmitnick 3:32 pm on February 17, 2017 Permalink | Reply
    Tags: A minimal extension to the standard model of particle physics involves six new particles, Astrophysical observations suggest that the mysterious dark matter is more than five times as common, , DESY Flash, Model Tries to Solve Five Physics Problems at Once, Physical Review Letters, , , The particles are three heavy right-handed neutrinos and a color triplet fermion and a particle called rho that both gives mass to the right-handed neutrinos and drives cosmic inflation together with   

    From DESY: “Solving five big questions in particle physics in a SMASH” 

    DESY
    DESY

    2017/02/16
    No writer credit found

    Extension of the standard model provides complete and consistent description of the history of the universe.

    The extremely successful standard model of particle physics has an unfortunate limitation: the current version is only able to explain about 15 percent of the matter found in the universe.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Although it describes and categorises all the known fundamental particles and interactions, it does so only for the type of matter we are familiar with. However, astrophysical observations suggest that the mysterious dark matter is more than five times as common. An international team of theoretical physicists has now come up with an extension to the standard model which could not only explain dark matter but at the same time solve five major problems faced by particle physics at one stroke. Guillermo Ballesteros, from the University of Paris-Saclay, and his colleagues are presenting their SMASH model (“Standard Model Axion Seesaw Higgs portal inflation” model) in the journal Physical Review Letters.

    1
    The history of the universe according to SMASH, denoting the different phases and the dominant energies of the epochs since the Big Bang. Credit: DESY

    3

    Model Tries to Solve Five Physics Problems at Once

    A minimal extension to the standard model of particle physics involves six new particles. http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.118.071802

    The standard model has enjoyed a happy life. Ever since it was proposed four decades ago, it has passed all particle physics tests with flying colors. But it has several sticky problems. For instance, it doesn’t explain why there’s more matter than antimatter in the cosmos. A quartet of theorists from Europe has now taken a stab at solving five of these problems in one go. The solution is a model dubbed SMASH, which extends the standard model in a minimal fashion.

    SMASH adds six new particles to the seventeen fundamental particles of the standard model. The particles are three heavy right-handed neutrinos, a color triplet fermion, a particle called rho that both gives mass to the right-handed neutrinos and drives cosmic inflation together with the Higgs boson, and an axion, which is a promising dark matter candidate. With these six particles, SMASH does five things: produces the matter–antimatter imbalance in the Universe; creates the mysterious tiny masses of the known left-handed neutrinos; explains an unusual symmetry of the strong interaction that binds quarks in nuclei; accounts for the origin of dark matter; and explains inflation.

    The jury is out on whether the model will fly. For one thing, it doesn’t tackle the so-called hierarchy problem and the cosmological constant problem. On the plus side, it makes clear predictions, which the authors say can be tested with future data from observations of the cosmic microwave background and from experiments searching for axions. One prediction is that axions should have a mass between 50 and 200 μeV. Over to the experimentalists, then.

    This research is published in Physical Review Letters.

    “SMASH was actually developed from the bottom up,” explains DESY’s Andreas Ringwald, who co-authored the study. “We started off with the standard model and only added as few new concepts as were necessary in order to answer the unresolved issues.” To do this, the scientists combined various different existing theoretical approaches and came up with a simple, uniform model. SMASH adds a total of six new particles to the standard model: three heavy, right-handed neutrinos and an additional quark, as well as a so-called axion and the heavy rho (ρ) particle. The latter two form a new field which extends throughout the entire universe.

    Using these extensions, the scientists were able to solve five problems: the axion is a candidate for dark matter, which astrophysical observations suggest is five times more ubiquitous than the matter we are familiar with, which is described by the standard model. The heavy neutrinos explain the mass of the already known, very light neutrinos; and the rho interacts with the Higgs boson to produce so-called cosmic inflation, a period during which the entire young universe suddenly expanded by a factor of at least one hundred septillion for hitherto unknown reasons. In addition, SMASH provides explanations as to why our universe contains so much more matter than antimatter, even though equal amounts must have been created during the big bang, and it reveals why no violation of so-called CP symmetry is observed in the strong force, one of the fundamental interactions.

    3
    The particles of the standard model (SM, left) and of the extension SMASH (right). Credit: Carlos Tamarit, University of Durham

    “Overall, the resulting description of the history of the universe is complete and consistent, from the period of inflation to the present day. And unlike many older models, the individual important values can be calculated to a high level of precision, for example the time at which the universe starts heating up again after inflation,” emphasises Ringwald.

    Being able to calculate these values with such precision means that SMASH could potentially be tested experimentally within the next ten years. “The good thing about SMASH is that the theory is falsifiable. For example, it contains very precise predictions of certain features of the so-called cosmic microwave background. Future experiments that measure this radiation with even greater precision could therefore soon rule out SMASH – or else confirm its predictions,” explains Ringwald. A further test of the model is the search for axions. Here too, the model is able to make accurate predictions, and if axions do indeed account for the bulk of dark matter in the universe, then SMASH requires them to have a mass of 50 to 200 micro-electronvolts, in the units conventionally used in particle physics. Experiments that examine dark matter more precisely could soon test this prediction too.

    Javier Redondo from the University of Saragossa in Spain and Carlos Tamarit from the University of Durham in England were also involved in the study.

    Read the APS synopsis: http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.118.071802

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
  • richardmitnick 9:16 am on April 14, 2016 Permalink | Reply
    Tags: , DESY Flash,   

    From DESY: “First user operation at FLASH2” 

    DESY
    DESY

    1
    FLASH is the first X-ray laser worldwide which can serve experiments at two beamlines at the same time

    DESY/FLASH
    DESY/FLASH

    Since Friday, 8 April at 12:14 h FLASH is running in parallel operation for two user experiments, one in the experimental hall “Albert Einstein” (FLASH1) and one in the new hall “Kai Siegbahn” (FLASH2). First official FLASH2 users are the researchers around Sven Toleikis and Andreas Przystawik at beamline FL24 who focus the FLASH2 pulses with the help of a multilayer mirror onto rare gas clusters and study the fluorescence of the resulting nanoplasma as a function of cluster size.

    Right after the successful start last Friday the first record for this doubled user operation was set: On Saturday, FLASH delivered 4000 pulses per second with up to 140 micro joule (µJ) per pulse to an experiment of Mark Dean et al. (Brookhaven National Laboratory, New York) at FLASH1 beamline PG1 and in parallel 110 pulses per second with about 100 micro joule each for FLASH2 making it a successful start at both ends.

    The second free-electron laser line, FLASH2, has been realized from 2011 to 2015. Soon after the first successful generation of extremely intense FEL radiation on FLASH2 in August 2014, parallel operation of the two soft X-ray free-electron lasers, FLASH1 and FLASH2, has been established. Now, the first FEL beamline in the new hall “Kai Siegbahn” is operational making it possible to run two experiments simultaneously on FLASH1 and FLASH2, both delivering intense, ultra-short laser pulses with user-specific parameters.

    2
    Click me! First user experiment at FLASH2: fluorescence of Xe clusters excited by the FLASH2 pulses. Left: Nozzle where the clusters exit. Middle: fluorescence in the focus of the multilayer mirror (higher intensity left and right of the centre, since there are more clusters which fluoresce). Right (weaker ‘circles’): fluorescence of the clusters in the incoming unfocused FEL beam.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
  • richardmitnick 8:58 am on April 9, 2015 Permalink | Reply
    Tags: , , DESY Flash, ,   

    From XFEL: “European XFEL scientists look deep into the atom” 

    XFEL bloc

    European XFEL

    09 April 2015
    No Writer Credit

    Digging into the “Giant Resonance”, scientists find hints of new quantum physics

    A cooperation between theoretical and experimental physicists has uncovered previously unknown quantum states inside atoms. The results, described in a paper published today in the journal Nature Communications, allow a better understanding of some aspects of electron behaviour in atoms, which in turn could lead to better insights into technologically relevant materials.

    In this study, scientists from European XFEL and the Center for Free Electron Laser Science (CFEL) at DESY examined the unknown quantum states in atoms of the noble gas xenon using DESY’s X-ray laser FLASH.

    XFEL Campus
    XFEL

    DESY FLASH
    DESY FLASH

    The bright X-ray light of free-electron lasers such as FLASH and the European XFEL allowed the scientists to observe these states for the first time. (CFEL is a joint venture between DESY, the University of Hamburg, and the Max Planck Society.)

    Atoms can develop an electrical charge by losing or gaining one or more electrons. This process, called ionization, was thought to be fairly simple. As an electron departs, it can briefly “hang” between the different locations of electrons in the atom, also called “shells”. In the world of quantum mechanics, this brief pause—lasting less than a femtosecond, or a quadrillionth of a second—is enough to be measured as what is called a “resonance”.

    “In a resonance, the electrons are ‘talking’ to each other”, says Michael Meyer, a leading scientist at European XFEL. This conversation of sorts can be picked up on a spectrograph, and, in most atoms, it shows up in a very narrow energy range.

    Yet for the past half century, scientists also have noted a strange resonance in atoms of the noble gas xenon and some rare earth elements. In contrast to other resonances, it covers a very broad energy range. This became known as the “giant dipole resonance”. “There were no good tools to investigate the giant dipole resonance more deeply”, says Meyer. “But extreme-ultraviolet and X-ray FELs present an opportunity to re-examine xenon’s strange property.” Such facilities have the possibility of studying nonlinear processes, or phenomena that are not a direct result of a single interaction—in the case of photoionization the disappearance of one photon, with its energy being transferred to the electron that can thus escape the atom. The extraordinary intensity of FELs makes non-linear processes observable—in this case, a process whereby two photons disappear, simultaneously transferring their energy to the escaping electron.

    1
    Graphical representation of a 4d electron orbital in atomic xenon. Antonia Karamatskou / DESY

    This has become evident when Tommaso Mazza, a scientist in Meyer’s group at European XFEL, and others investigated the ionization of xenon atoms under intense FEL radiation at DESY’s FLASH. In parallel, DESY scientist Robin Santra, the leader of the CFEL theory group, and a student in his group, Antonia Karamatskou, thought there was something more to the giant dipole resonance. They worked off of a forty-year old suggestion that had been largely ignored: that xenon actually had not one but two resonances, and that earlier spectrographic techniques could not distinguish between them. In contrast, X-ray FELs can target very specific energies in the electronic structure of the atom using just two individual particles of light, enabling scientists to see both resonances more clearly.

    Santra and Karamatskou made calculations describing the energies of the resonances. The data from the experiments performed at FLASH by Tommaso Mazza and others match Santra’s and Karamatskou’s predictions. This is the first evidence of the giant dipole resonance being composed of two other resonances.

    Both Santra and Meyer think that there is far more to the behaviour of electrons within atoms in general than has been previously understood. The result point to not yet fully understood aspects of how atoms function.

    “We don’t even yet understand why there might be a second resonance”, Santra says. “Many people think simple atomic physics is figured out, but as this collaboration has shown, there is a lot of hidden stuff out there!”

    Also, the experiment has shown that FELs can be highly sophisticated tools for studying quantum physics. Santra says he expects the European XFEL, which is due to open to users in 2017, to expand these possibilities even further.

    The research collaboration between Meyer and Santra was initiated and supported by the Collaborative Research Center at the University of Hamburg, SFB 925.

    “Sensitivity of nonlinear photoionization to resonance substructure in collective excitation”; T. Mazza, A. Karamatskou, M. Ilchen, S. Bakhtiarzadeh, A.J. Rafipoor, P. O’Keeffe, T.J. Kelly, N. Walsh, J.T. Costello, M. Meyer & R. Santra; Nature Communications, 2015; DOI: 10.1038/ncomms7799

    See the full article here.

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    XFEL Campus

    The Hamburg area will soon boast a research facility of superlatives: The European XFEL will generate ultrashort X-ray flashes—27 000 times per second and with a brilliance that is a billion times higher than that of the best conventional X-ray radiation sources.

    The outstanding characteristics of the facility are unique worldwide. Starting in 2017, it will open up completely new research opportunities for scientists and industrial users.

     
  • richardmitnick 9:20 am on March 13, 2015 Permalink | Reply
    Tags: , , DESY Flash,   

    From DESY: “Molecules perform endless cartwheels” 

    DESY
    DESY

    2015/03/13
    No Writer Credit

    1
    An near-infrared laser (red) makes the originally disordered molecules perform synchronized cartwheels so that all the molecules at a particular position along the beam are oriented in the same direction. Picture: Jens S. Kienitz/CFEL, DESY and CUI

    Scientists in Hamburg have resorted to a physical trick to persuade entire groups of molecules to perform synchronized cartwheels, virtually endlessly. This technique opens up new opportunities for imaging molecules and their chemical dynamics. Prof. Jochen Küpper and his team at the Center for Free-Electron Laser Science (CFEL) are presenting their findings in the journal Physical Review Letters.

    2
    The FLASH experimental hall with beamlines which guide the laser-like light of the free-electron laser FLASH to the experimental stations. (Source: DESY)

    Intense flashes of x-rays emitted by so-called free electron lasers offer detailed insights into the world of molecules. Researchers use them, for example, to explore the atomic structure of biomolecules and to better understand their function, or they try to film dynamic processes taking place in the nanocosm – such as the excitation cycle in photosynthesis. Until now, however, such molecules have generally had to be available in a crystalline form for such examinations to be carried out, because the individual molecules alone do not produce a strong enough signal. In a crystal, the molecules are arranged in regular patterns so that the signals from each add up, allowing an analysis on an atomic level.

    “Crystals represent a very special state, however – often imposed and unnatural”, explains Sebastian Trippel, the first author of the paper. Scientists would therefore often prefer to examine free molecules directly. But how can such free molecules be moved, in a controlled fashion, into the x-ray beam of a free electron laser? Scientists have been experimenting with different methods of guiding the molecules, using electromagnetic fields and laser light, and aligning them in a particular direction at the same time.

    They have already succeeded in strongly orienting entire ensembles of molecules in the same direction for such examinations, “however when you do this, the molecular ballet is influenced by an electromagnetic field, which can in turn have an unwanted effect on the measurements,” explains Jochen Küpper, a scientist at DESY, who is also a member of the Hamburger Center for Ultrafast Imaging (CUI) and a professor at the University of Hamburg. The molecular tamers working with Küpper have now found a way of preserving the alignment of molecular ensembles even after the laser field has been switched off.

    For their test, the researchers used carbonyl sulfide (OCS) as a simple model system. The three atoms that make up this molecule (carbon, oxygen and sulfur) lie in a straight line, and this simple structure makes it particularly suitable for demonstrating the method. The scientists released high-pressure carbonyl sulfide molecules into a vacuum chamber through a fine nozzle, as a result of which the gas expanded and thereby cooled down rapidly. They then used a so-called deflector, a kind of prism for molecules, to fish out those molecules that were in the lowest-energy state.

    A tailored pulse of infrared laser light mixed this state with the first excited quantum state. As a result, the molecules started to perform, synchronously, a so-called inversion, whereby the individual molecules fell in step with each other, so that the sulphur atom (S) of the molecules all simultaneously pointed up or down. This inversion continued undiminished even after the molecules had passed the infrared laser and were moving through space without being affected by an alternating electromagnetic field. “In a sense, the laser forces the molecules to perform synchronous cartwheels, which would continue forever if they didn’t eventually reach the walls of the experimental apparatus”, Trippel explains.

    The molecules travel an almost infinite distance compared with the period of their inversion – they have enough time to perform hundreds of thousands of cycles of this motion before they collide with the wall of the vacuum chamber. For experimenters, this offers some very tangible advantages: all they have to do in order to select a specific orientation of the molecular ensemble under scrutiny – in which the two orientations alternate regularly – is to select the appropriate moment in time behind the laser beam.

    This method not only works for the two lowest energy states, but in principle for all states of a linear molecule, as the researchers point out in their paper. “This targeted molecular choreography opens up new possibilities for holding ensembles of free molecules in the x-ray beam of a free electron laser in a controlled fashion, so that they can be investigated there,” says Küpper.

    Reference:
    Two-state wave packet for strong field-free molecular orientation; Sebastian Trippel, Terry Mullins, Nele L. M. Müller, Jens S. Kienitz, Rosario González-Férez and Jochen Küpper; Physical Review Letters, 2015; DOI: 10.1103/PhysRevLett.114.103003

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
  • richardmitnick 10:09 am on January 30, 2015 Permalink | Reply
    Tags: , DESY Flash   

    From DESY: “Free-electron laser FLASH” 

    DESY
    DESY

    10 years of SASE at FLASH

    Back in 2005, early in the morning of January 14th, first SASE has been observed at DESY’s newly installed VUV free-electron laser. The electron beam has been accelerated to 445 MeV corresponding to a wavelength of 32 nm. In summer 2005, the VUV-FEL turned into a user facility named FLASH.

    1
    Spectrum of the first SASE signal measured in the early morning of January 14th, 2005.

    FLASH2 generates first laser light

    The FLASH II project – the extension of the free-electron laser FLASH – has reached an important milestone: On 20 August 2014, at 20:37 h, the accelerator team of the late shift was able to detect the first laser light at the new undulator line named FLASH2. Simultaneously, FLASH´s first undulator line FLASH1, which is provided with electron bunches from the same accelerator, could continue to operate without restrictions. The undulators are periodic structures of magnets with alternating North-South polarity in which the X-ray laser light is generated. “This makes FLASH the world’s first free-electron laser that serves two laser lines simultaneously and independently from each other,” says project leader Bart Faatz

    2
    SASE FEL radiation observed on a Ce:YAG screen of the FLASH2 photon beamline.

    Fifth user period started 24-Feb-2014 with its first beam time block

    Coming out of a long shutdown to finish up the construction of the new beamline FLASH2, the fifth user period for beamline FLASH1 has started end of February with its first user block. Until April 2015, more than 5000 hours of user experiments are scheduled. Beam time will also be available for accelerator and photon beam line studies as well as for FLASH2 commissioning. FLASH2 saw first beam in March 2014 pushing the beam to the dump for the first time May, 23. Since then, FLASH2 is operated in parallel to FLASH1 whenever possible to finish up the commissioning of beam diagnostics and to refine beam optics. First SASE radiation at 40 nm has been seen on Aug 20, 2014. The next goal is to characterize the SASE radiation, to measure gain length for example for as many other wavelength.

    4
    Schematic layout of FLASH. Not to scale. The second beamline, FLASH2, is being commissioned and has seen first lasing at 40 nm on Aug, 20 2014 while FLASH1 was at the same time providing 250 pulses long bunch trains for experiments.

    FLASH is a soft X-ray free-electron laser

    FLASH, the world’s first soft X-ray free-electron laser (FEL), is available to the photon science user community for experiments since 2005. Ultra-short X-ray pulses as short as 50 femtoseconds are produced using the SASE process. SASE is an abbreviation for Self-Amplified Spontaneous Emission. The SASE or FEL radiation has similar properties than optical laser beams: it is transversely coherent and can be focused to tiny spots with an irradiance exceeding 1016 W/cm2.

    The SASE process is driven by a high brightness electron beam. The wavelength of the X-rays is tuned by choosing the right electron energy. The FLASH accelerator provides a range of electron energies between 0.37 and 1.25 GeV covering the wavelength range between 45 and 4 nanometers (nm). See the table below for details.

    An electron gains an energy of 1 electron volt (1 eV) moving across an electric potential difference of one volt (1 V). One gigaelecton volts (GeV) is a thousand million volts. Visible light has a wavelength between 380 and 760 nm. 1 nm is a millionth of 1 mm. The size of molecules is around 1 nm

    Temp
    FLASH accelerating modules. Seven modules are installed, each module has a length of 12 m.

    FLASH reaches the water window

    The FLASH accelerator is equipped with seven TESLA-type 1.3 GHz superconducting accelerator modules. Each 12 m long module contains eight cavities. The 1 m long cavities are made of solid niobium and cooled by liquid helium at 2 K. At this temperature just 2 dgC above the absolute zero, niobium is superconducting so that the acceleration field can be applied with very small losses. This makes a superconducting accelerator very efficient.

    In September 2010, the FLASH team operated the accelerator with an electron energy of 1.25 GeV producing X-rays with a wavelength of 4.12 nm. For the first time FLASH has generated laser light in the so-called water window with the fundamental wavelength. So far this was only possible at FLASH with the by a factor of thousand fainter third and fifth harmonic of the fundamental.

    The water window is a wavelength region between 2.3 and 4.4 nanometers. In the water window, water is transparent for light, i.e. it does not absorb FEL light. This opens up the possibility to investigate samples in an aqueous solution. This plays an important role especially for biological samples, because carbon atoms in these samples are highly opaque to the X-ray radiation, while the surrounding water is transparent and therefore not disturbing.

    FEL Radiation Parameters 2012

    Parameter Value

    WavelengthRange 4.2 – 45 nm

    Average Single Pulse Energy 10 – 500 µJ

    Pulse Duration (FWHM) <50 – 200 fs

    Peak Power (from av.) 1 – 3 GW

    Average Power (example for 5000 pulses/sec) up to 600 mW

    Spectral Width (FWHM) 0.7 – 2 %

    Photons per Pulse 1011 – 1013

    Average Brilliance 1017 – 1021 photons/s/mrad2/mm2/0.1%bw

    Peak Brilliance 1029 – 1031 photons/s/mrad2/mm2/0.1%bw

    FLASH is a science driver

    Many scientific disciplines ranging from physics, chemistry and biology to material sciences, geophysics and medical diagnostics use the powerful soft X-ray source FLASH. The ultra-short X-ray pulses in the femtosecond range allow experiments which are not possible otherwise. For example, time-resolved observation of chemical reactions with atomic resolution, single shot diffraction imaging, and many others.

    More than 200 publications on photon science have been published already, many in high ranked journals.

    First external seeding at 38 nm

    In April 2012, sFLASH, the seeding experiment at FLASH, has obtained first seeding at 38 nm. An external seed source of the same wavelength overlaps with the electron beam to seed the SASE process in a series of undulators installed between the accelerator and the FLASH undulators.

    The FLASH Accelerator

    FLASH is a high-gain free-electron laser (FEL) which achieves laser amplification and saturation within a single pass of the electron
    bunches through a long undulator section. The lasing process is initiated by the spontaneous undulator radiation. The FEL works in the so-called Self-Amplified Spontaneous Emission (SASE) mode without needing an external input signal.The electron bunches are produced in a laser-driven photoinjector and accelerated by a superconducting linear accelerator. The RF-gun based photoinjector allows the generation of electron bunches with tiny emittances – mandatory for an efficient SASE process.The superconducting techniques allows to accelerate thousands of bunches per second, which is not easily possible with other technologies. At intermediate energies of 150 and 450 MeV the electron bunches are longitudinally compressed, thereby increasing the peak current from initially 50-80 A to 1-2 kA – as required for the lasing process in the undulator.

    A special superconducting 3.9-GHz module built at Fermilab has been installed in 2010 to improve the quality of the accelerated electron beam. The four cavities in this module operate at the third harmonic of the acceleration field frequency. They shape the electron bunches in a way that the intensity of the laser light is higher than ever before.

    Temp
    The FLASH undulators

    The 27 m long undulator consists of permanent NdFeB magnets with a fixed gap of 12 mm, a period length of 27.3 mm and peak magnetic field of 0.47 T. The electrons interact with the undulator field in such a way, that so called micro bunches are developed. These micro bunches radiate coherently and produce intense X-ray pulses. Finally, a dipole magnet deflects the electron beam safely into a dump, while the FEL radiation propagates to the experimental hall.

    7

    See the full article here.

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    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

     
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