February 2010

Are we alone?

January 2010

How many atoms does one need to form a metal?

Abstract
Elementary courses of physics and chemistry teach us, on one side, about separate metal atoms with a certain amount of bound electrons, and on the other side – about ”infinitely”-large bulk metals with freely-moving electrons capable of conducting electric current. If one now starts building an “infinite” solid-metal atom by atom – what properties does the intermediate agglomerate of a finite amount of atoms have? Will it be metallic – meaning, first of all, will it conduct electricity? These questions are not just of “pure-science” interest. In view of modern electronics’ development towards the ultimate miniaturization, a practical question arises – will the metal connections in our computers conduct the electricity at any dimension? It appears that the electricity-conducting properties emerge in the agglomerate of atoms somewhere on the way from separate atoms to the “infinite” conventional metals. It often happens that conductivity properties set on when such agglomerates, also known as clusters, contain just a few tens of atoms, like for tin, or a few hundreds – like for copper. During the last two decades it has become possible to monitor the transition to metallic properties with the size of metal clusters at well-controlled laboratory conditions. State-of-the-art-experiments in this field brought a Noble prize in 1996 as a side-development of one of the projects. Electron spectroscopy has been a decisive probing technique in disclosing the details of the transition to metallic properties. The presentation will briefly dwell on the theoretical expectations for the properties’ transformation, as well as – in more details – on the experimental methods and results demonstrating this transformation.

Perspectives for Neutron detector prospects at ESS

More information...

Seminars 2009

December 2009

Construction and initial testing of a neutron detector prototype

Abstract
This project involved the construction and testing of a neutron-detector
prototype. The main work was carried out at the Tagged-Photon Facility at MAX-lab in Lund, Sweden. The detector was constructed using NE213 liquid scintillator and an aluminum container box. An initial test of the detectors performance was commissioned using the tagged-photon beam. Results are presented and discussed.

Ground Motion Measurements at various sites and Mechanical Stability of Structures

Charles Darwin - his life and research

November 2009

Variation in moth pheromones: From chemical to genomic analysis in 25 years...

How to create an academic poster

Abstract
Creating a poster for the first time is a lot of fun, but also a lot of hard work, for everyone involved
(and for those close by...).

October 2009

The use of ionizing radiation in cancer diagnostics and treatment

The European Theoretical Spectroscopy Facility:
Towards a new model for the interaction between theorists and experimentalists

Abstract
The field of first-principles simulation of materials and nanosytems has seen an amazing development in the past twenty years. Moreover, current frontier-of-knowledge research often stems from fruitful collaborations between theorists and experimentalists. Still, until several years ago, there was no easy way for an experimentalist to know which theorist would be best able to help him/her, e.g. to understand his/her experimental results.

I will present the European Theoretical Spectroscopy Facility (ETSF), a new virtual infrastructure (http://www.etsf.eu), knowledge center for theoretical spectroscopy.The ETSF gathers the experience and know-how of more than 200 researchers in Europe and the United States, facilitating collaborations and rapid knowledge transfer. The ETSF offers its expertise to researchers, industry, and students in the form of collaborative projects, free scientific software and training. Proposals to benefit from these services can be submitted at any moment, and are evaluated twice a year by an external scientific panel.

I will also present ABINIT, one of the software application that is delivered by the ETSF. In order to cope with the increasing software complexity, it became apparent, about a decade ago, that software engineering techniques and a group collaborative effort would be major ingredients of a successful first-principles project. Following the model of the Linux operating system development, the open source ABINIT project was launched in 1997.

As of know, there are more than 1000 mailing addresses in the main mailing list, and about 40 active contributors.

Lithosphere and Biosphere Science: Fossil plants - a tool to reconstruct extinction events and climate in Earth's history

September 2009

Beam loss mechanisms in relativistic heavy-ion colliders

Abstract
The Large Hadron Collider (LHC), the largest particle accelerator ever built, is presently under comissioning at the European Organization for Nuclear Re- search (CERN). It will collide beams of protons, and later Pb ions, at ultrarelativistic energies. Because of its unprecedented energy, the operation of the LHC with heavy ions will present beam physics challenges not en- countered in previous colliders. Beam loss processes that are harmless in the presently largest operational heavy-ion collider, the Relativistic Heavy Ion Col- lider (RHIC) at Brookhaven National Laboratory, risk to cause quenches of superconducting magnets in the LHC.

Interactions between colliding beams of ultrarelativistic heavy ions, or between beam ions and collimators, give rise to nuclear fragmentation. The resulting isotopes could have a charge-to-mass ratio different from the main beam and therefore follow dispersive orbits until they are lost. Depending on the machine conditions and the ion species, these losses could occur in localized spots, where the induced heating risks to the quench the superconducting magnets.

Apart from detailed studies of these beam losses, simulations of the ion luminosity time evolution at RHIC and LHC are presented and compared with a large amount of data from RHIC.

Synchrotron light and the MAX-lab accelerators

Network performance - Evaluation of High-Performance Network Technologies

Abstract
Any large physics facility, such as a light or a neutron source, needs a mechanism for hard real-time communication between its distributed nodes to provide a fast feedback system, video and large data transfers.

I will discuss some combinations of common off-the-shelf (COTS) technologies that allow the above systems to be implemented, such as RT-linux, PXI, GB Ethernet, CISCO switches, Micro Research Finland's timing and event solution, and GigE audio-video streaming. Also, I present the performances achieved in a practical (though small scale) technology demonstrator, which we have done for ITER.

In particular, three types of high-performance communication will be adressed.

• A high throughput data network to distribute measurements (estimated to about 5000 double-valued signals) across the system to allow for 1kHz control loops;
• an Event Distribution and Timing Network to allow synchronization of node I/O operations to 10ns;
• an Audio Video Network to provide sufficient bandwidth for streaming of surveillance and diagnostics video at a high resolution (1024x1024) and frame rate (30Hz).

X-ray scattering investigations of the nanoscale structure and dynamics of soft matter

Abstract
In this talk, I shall give an overview of different possibilities offered by synchrotron X-ray scattering techniques in the investigation of soft matter systems. The present trend is sequel to a combination of factors, most notably the developments in X-ray instrumentation and parallel advancements of data analysis methods. This will be illustrated by several examples starting from model colloids to highly self-assembled soft matter systems. I shall then outline some challenges and most notable improvements expected within the ESRF Upgrade Programme. In order to exploit these instrument developments, we are in the process of establishing a Partnership for Soft Condensed Matter together with the Institute Laue-Langevin and the joint user community.

New Frontiers for High-Resolution Soft X-Ray RIXS at the SLS

Abstract
Resonant inelastic X-ray scattering (RIXS) is a powerful bulk-sensitive photon-in / photon-out spectroscopic probe of the electronic structure of condensed matter with atomic and orbital sensitivity. It is a unique tool for studying excitations from the electronic ground state in transition-metal oxides, being directly sensitive to charge-, orbital- and spin-degrees of freedom. Dedicated instrumentation for soft X-ray RIXS with ultra-high resolution has become available for users at the ADvanced RESonant Spectroscopies (ADRESS) beamline [1] at the Swiss Light Source (SLS).

We report on construction and capabilities of the ADRESS beamline at the SLS. Its optical scheme is based on a Plane Grating Monochromator operated in collimated light. The beamline is calculated to deliver soft X-rays with variable polarization (circular and linear) between 0.4 and 1.8 keV at high resolving power up to 33000 near 1 keV. The flux of 1 keV photons on the sample ranges from 3x10¹¹ to 1x10¹³ photons/s/0.01%BW for a resolving power of 33’000 and 10’000, respectively. The undulator for this beamline adopts an Apple-type scheme with 4 arrays of permanent magnets with a fixed magnetic gap. In this design horizontal movements of the magnetic arrays are used to adjust polarization (opposite arrays) and photon energy (two adjacent arrays). Ellipsoidal refocusing optics in front of the experimental station for the RIXS investigations reduces the vertical beam dimension on the sample to below 6 um as required for high detection efficiency of the inelastically scattered X-rays.

The SAXES (Super Advanced X-ray Emission Spectrograph) RIXS spectrometer [2] of the ADRESS beamline is based on a variable line spacing spherical grating and has a resolving power of ca. 12000 for 1 keV. It is installed on a rotating platform in order to study low-energy excitations as a function of momentum transfer, thereby enabling characterization of localized vs. delocalized character of electronic excitations. We demonstrate the unique opportunities of this set-up in exemplifying RIXS studies on Sr₁₄Cu₂₄O₄₁ [3] and VO₂.

References:
[1] V. N. Strocov, T. Schmitt et al., http://sls.web.psi.ch/view.php/beamlines/adress/index.html
[2] G. Ghiringhelli et al., Rev. Sci. Instrum. 77, 113108 (2006).
[3] J. Schlappa, T. Schmitt, F. Vernay, V. Strocov et al., Phys. Rev. Lett. 103, 047401 (2009)

August 2009

Design of a 100K-resolving-power beamline in Shanghai and a 5-GeV synchrotron in Beijing

Coherent Soft X-ray beamline (CSX): A High coherent flux and full polarization control beamline at NSLS-II project

Abstract
We are currently in the design phase of the NSLS-II coherent soft x-ray project beamline. In this phase we are optimizing the optical layout and improving the choice of insertion device for a beamline capable of providing in one branch, fast (>20 Hz) polarization switching that enable sensitive polarization-dependent soft x-ray (260-1600 eV) absorption and scattering measurements of polarization sensitive systems and a second branch optimized to provide with high coherent flux for typical photon hungry experiments such as coherent scattering or imaging.

Because this is the only beamline dedicated to soft x-rays among the project beamlines, we are planning to have an operation mode where both branches can operate simultaneously. One candidate source configuration (and the present baseline configuration) consists of two canted 2 m-long APPLE II elliptically-polarized undulator (EPU) insertion devices. Each EPU would be set to provide a different beam polarization (e.g. right or left circular, linear horizontal or vertical). And for the coherent branch the EPUs are going to operate inline. Each branch has a different goal that has been careful considered in the optical layout, i.e. the optical configuration preserves the beam polarizations in the full polarization control branch, and intend to preserve the "natural" coherence of the source in the high coherent flux branch.

June 2009

The CLIC damping rings and the next generation of accelerators at CERN

Abstract
Yannis Papaphilippoiu will give a presentation about the CLIC damping rings and the next generation of accelerators at CERN. (more text will be added)

Accelerator physics studies of the MAX-lab storage rings

Abstract
Within research, synchrotron radiation is a highly useful probe for the study of materials, their properties and structures. Currently, no other radiation source allows the combination of high intensity and short wavelengths.

The 3rd generation light sources currently in use for the production of synchrotron radiation are however considerable investments: for already existing facilities this makes it important to ensure high operational reliability as well as good performance. For facilities in planning, such as the MAX IV light source, extensive design studies are of essence to meet target performance.

The main subject of this thesis is the performance, characterisation and tuning of the existing MAX II and MAX III light sources at the MAX-laboratory, one of two national research facilities in Sweden.

The MAX II storage ring, in operation since 1995, was characterised using response matrix analysis, bunch spectrum analysis and transverse beam profile measurement. In particular, some at the time of building unconventional technology solutions were evaluated: combined quadrupole-sextupole magnets, non-zero dispersion in straight sections and common girders for all magnets in one cell.

The MAX III storage ring, commissioned in 2007 and starting synchrotron radiation production in late 2008, was characterised using response matrix and bunch spectrum analysis. Further, measurements were carried out of the betatron tunes, chromaticities, beam lifetime, magnets, pole-face strips as well as the RF parameters. Accurate characterisation of MAX III served dual purposes: improvement of MAX III performance and evaluation of new accelerator technology intended also for the MAX IV project.

Initial MAX III operational experience showed that the dipole magnets used for orbit correction frequently saturated. To remedy this problem, the ring was realigned using the beam as a reference. The data required was the corrector magnet strengths.

The thesis also encompasses some intra beam scattering studies for two versions of a prototype multi-bend achromat lattice: a 12 cell and a 20 cell version. The lattice was designed for low-emittance light sources and is used as the basis of the MAX IV storage ring.

May 2009

Synchrotron-based Tomographic Microscopy: fast, high-sensitive and high-resolution 3D imaging at the micron- and nano scale

Abstract
Synchrotron-based Tomographic Microscopy is a powerful technique for fast non-destructive, high resolution quantitative volumetric investigations on samples of diverse nature. At the Swiss Light Source of the Paul Scherrer Institut, a beamline for Tomographic Microscopy and Coherent radiology experiments (TOMCAT) has been recently put into operation. This beamline gets synchrotron light from a 2.9 T superbend and the main optical component, a Double Crystal Multilayer Monochromator, covers an energy range between 8 and 45 keV. The standard TOMCAT detector offers field of views ranging from 0.75x0.75 mm² up to 15x15 mm² with a theoretical pixel size of 0.37 um and 7.4 um, respectively.

The beamline design and flexible endstation setup make a large range of investigations possible. In addition to routine measurements which exploit the absorption contrast, the high coherence of the source also enables phase contrast tomography, implemented with two complementary techniques based on a modification of the Transport of Intensity method and grating interferometry. In-situ experiments are also routinely conducted.

Typical acquisition times for a tomogram are in the order of few minutes, ensuring high throughput and allowing for semi-dynamical investigations. Raw data are automatically post-processed online and full reconstructed volumes are available shortly after a scan with minimal user intervention.

This talk gives an overview of the TOMCAT beamline introducing different microtomographic approaches (in-line imaging, full-field microscopy, phase contrast and dark-field imaging) and discusses a selection of applications of this versatile technique in life and materials science. Examples range from the visualization of cellular structures in bone samples to the quantification of vascular micro-architecture in the brain. Other applications go from the high-resolution, non-destructive investigations of the internal structure of invaluable and unique fossilized specimens to the quantitative analysis of pore networks in diverse rock types, for instance for improving oil recovery, understanding element mobilization by hydrothermal fluids, studying dynamics of volcanic eruptions or refining current contaminant diffusion models. In-situ (e.g. cryotomography) and semi-dynamical (e.g. compression, crack) experiments will also be discussed.

Studies on high brightness electron beams for short pulses and free electron laser

Collective effects in a high brightness electron pulse driver

Universums tidigaste historia

April 2009

ISA and the Astrid-2 project

The Optical Replica Synthesizer for FLASH, DESY

March 2009

Optics corrections at the SLS storage ring

How animals see the world

Recent polarization experiments on the nucleon at the Laser Electron Gamma Source

Abstract
The Laser Electron Gamma Source (LEGS) facility operated at Brookhaven National Laboratory from 1990 through 2006, producing polarized gamma ray beams by backscattering laser light from 2.8 GeV electrons stored in a ring of the National Synchrotron Light Source. The high degree of easily changeable polarizations allowed the simultaneous measurement of several different spin matrix elements in pion photoproduction from the proton and deuteron. Implications for the convergence of the Gerasimov-Drell-Hearn sum rule will be discussed.

January 2009

Fossil plants - a tool to reconstruct extinction events and climate in Earth's history

Seminars 2008

November 2008

Operation of the LHC with Pb82⁺ ions

The Large Hadron Collider at CERN will collide high energy protons, but later also heavy ions, starting with Pb82⁺ at an energy of 0.57 PeV. This opens up a new regime not only in the experimental study of nuclear matter, but also in the beam physics of hadron colliders.

In this presentation, an overview of the LHC Pb82⁺ ion runs will be given, with emphasis on the collider operation and performance limits.

October 2008

The Stucture of Multi-layer Epitaxial Graphene on Silicon Carbide

Graphene, a single sheet of carbon atoms sp2-bonded in a honeycomb lattice, is a possible all-carbon successor to silicon electronics. Ballistic conduction at room temperature and a linear dispersion relation that causes carriers to behave as massless Dirac fermions are features that make graphene promising for high-speed, low-power devices. The critical advantage of epitaxial graphene (EG) grown on SiC is its compatibility with standard lithographic procedures.

Surface X-ray Diffraction (SXRD) and Scanning Tunneling Microscopy (STM) results will be presented on the domain structure, interface composition and stacking character of graphene grown on both polar faces of semi-insulating 4H-SiC. Specular X-ray reflectivity measurements show that both faces have a carbon rich, extended interface that is tightly bound to the first graphene layer, leading to a "buffering effect" that shields the first graphene layer from the bulk SiC. In-plane X-ray crystal truncation rod analysis indicates that rotated graphene layers are interleaved in C-face graphene films and corresponding superstructures are observed in STM topographs. These rotational stacking faults in multilayer C-face graphene preserve the linear dispersion found in single layer graphene, making EG electronics possible even for a multilayer material.

August 2008

Some Thoughts Regarding a Design of Optical Systems Using Reflective Optics

Including the description about development of the optical system for measuring electron bunch length and longitudinal phase space at PITZ-DESY.

Some Thoughts Regarding Image Processing Techniques

Containing a description about applications of image processing algorithms in medical and industrial applications.

June 2008

fs-ESCA at the FLASH:
Towards Time-Resolved Core Level Photoelectron Spectroscopy on Solids at Free Electron Lasers

Abstract
Electron transfer in matter governs many basic processes in technology and nature due to its responsibility for chemical reactions and bonding. To access information on these dynamic processes, it is essential to directly observe the temporal evolution of the electronic structure at a defined atomic center -- a task which can only be performed with time resolved spectroscopical methods where spectroscopy with soft X-rays ensures the element specificity and chemical selectivity of the measurements.

The optical laser driven VUV sources typically used for time resolved spectroscopy only provide comparatively low intensities. This limitation can be overcome with the Free Electron Laser in Hamburg (FLASH) and brilliant X-ray pulses up to 200~eV photon energy with less than 30~fs pulse duration can be produced.

We have have worked to establish electron spectroscopy at FLASH as a tool to investigate ultrafast dynamics at solids and their surfaces. This is the foundation for femtosecond time-resolved electron spectroscopy for chemical analysis (fs-ESCA) on a solid surface using FLASH in combination with a synchronized optical Laser. To this end, it is necessary to determine the applicability range of electron spectroscopy using ultrashort x-ray pulses which is limited by space charge effects. By experimental and theoretical studies, a working range below the space charge limit is defined and estimations for future experiments can be made. In the next experimental step, an optical laser is synchronized with FLASH. Sideband generation on a metal surface is applied as a tool for cross correlation between the fs X-ray and optical pulses to obtain the additional temporal information needed for fs-ESCA. With both spatial and temporal overlap adjusted, first pump-probe experiments on solids are performed and solid state dynamics are studied. The surface photovoltage dynamics at the Ge surface is presented as a model for fs-ESCA.

March 2008

Seeded harmonic generation at Elettra storage ring Free Electron Laser

Abstract
Nowadays there is a strong need of coherent and intense radiation in many research disciplines. Free Electron Lasers (FELs) can provide ultra-short pulses in a wide spectral range with brightness orders of magnitude bigger than synchrotron light sources.

In this talk we present the experimental results obtained at the Elettra storage ring where a "single- pass" coherent harmonic generation has been implemented using the existing optical klystron. After reviewing the experimental setup, we present here the temporal and spectral characterization of the harmonic pulse. Measured peak power in the working wavelength range (i.e., 260-130 nm for the reported experiments) is several orders of magnitude above spontaneous synchrotron radiation.

Presently, the Elettra SRFEL is the unique facility simultaneously able to provide coherent optical pulses with different durations (100 fs - 1 ps), significant power (~1 MW) and variable polarization in a wide VUV spectral range (down to 100 nm). The Elettra SRFEL is an ideal test bed for the next generation of single-pass FELs.

Synchrotron SAXS experiments in polymer materials.
Instrumentation and morphological studies.

Abstract
In the design of new nanostructured material, the possibility of tailoring the final physical properties of polymer blends, block copolymers and clay/polymer nanocomposites choosing the appropriate mixture of chemical components is well known. The resulting structure and morphology define the principal physico-chemical properties of the material and its potential applications.

In this talk we discuss morphological aspects and phase transitions in dense polymeric systems using small angle x-ray scattering (SAXS). Structural, thermodynamic and kinetical parameters of polymer materials were determined in specifically defined experimental procedures. The use of synchrotron radiation and faster position sensitive X-ray detectors permitted time resolved data collection with some seconds of resolution. Special remarks concerning to in situ thermal and magnetic field treatments are discussed for two polymeric systems.

February 2008

Crystallographic studies on LlPR10 proteins from yellow lupine

Abstract
Pathogenesis-related (PR) proteins belong to a group of defense-related plant proteins, which are induced by different stress factors. These proteins play an important, yet not fully understood role in the pathogenesis and symbiosis processes in the plant kingdom. The function of the PR10 proteins in plant organisms is still not established.

The main objects of this investigations are proteins from two groups of LlPR10 proteins from yellow lupine (Lupinus luteus). In this work two aspects were discussed:
- methodological aspect which contains researches on the influence of different cryoprotection methods usage on the quality of the LlPR10.1B high resolution structures,
- research aspect which includes studies on binding properties of LlPR10.1A and 1B proteins and structure determination of two proteins from LlPR10.2 group - 2A and 2F.

Results of conducted researches gave some interesting informations about properties of LlPR10 proteins and they approach the answer about their possible function in plant organisms.

Boosting Molecular Replacement by adding anomalous scattering data

Abstract
Previous use of anomalous data in Molecular Replacement generally concerns excluding false hits in Molecular Replacement or calculating a unbiased electron density map when a solution has been found. In a proof of principle study we analyze the combined use of real and anomalous data in the rotation function. Diffraction data sets of 18 examples where collected at a wavelength of 2.0 Å and subsequently carefully scaled. Results show that in more difficult cases, where the correct solution of a rotation search is not obviously found, the correct rotation function peak may be substantially improved when information from anomalous scattering is included. This approach potentially allows Molecular Replacement to solve more structures where the anomalous substructure is known.

January 2008

Determination of large protein structures with SAD

Abstract
The complement system is a system of proteins present in blood and is a part of the innate immune system. The structures of two paralogous ~200 kDa proteins that are central to complement function were solved with SAD data. Using SAD phasing proved essential in both cases because of various difficulties with crystal systems and non-isomorphism.

Thin films at interfaces investigated by X-ray scattering

Kristian Kjær
Niels Bohr Institute, University of Copenhagen, Denmark
and
Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.

Abstract
The structures of thin films of organic molecules at interfaces have been studied by means of Synchrotron X-ray scattering. The films can be so-called Langmuir monolayers investigated in situ at the air-liquid interface; or bilayers or multilayers transferred onto solid support by the Langmuir-Blodgett technique. By suitable choice of the constituent amphiphilic molecules we may construct systems that serve as models for various types of biological membranes; or the molecules may have electrical/optical properties that are of interest for devices; or we may choose the simplest amphiphilic molecules and explore the basic physics of the resulting quasi-two-dimensional flatland. The experimental methods will be described along with results for a number of systems.

Seminars 2007

December 2007

Beam Losses from Bound Free Pair Production in Heavy Ion Colliders

Roderik is a part of the group of Accelerator Physics at MAX-lab, but his experimental work is carried out at CERN. His work on Accelerator Physics at CERN is focused on the LHC project. The LHC is to be used to accelerate and collide heave ions.

Abstract
The performance of the LHC as a heavy ion collider may be limited by a number of electromagnetic interactions at the interaction points, where Bound Free Pair Production (BFPP) is the most serious one. This process creates wrongly charged ions which can be lost in superconducting magnets, risking to quench them. First, measurements of this effect from Cu-operation at RHIC is presented, where losses were detected by an array of photodiodes downstream of the interaction point. After that, predictions are made for the LHC. Impact positions of BFPP particles are found using tracking from all interaction points that might collide ions, and positions of beam loss monitors are proposed to survey the losses caused by BFPP.

FLUKA

Abstract
FLUKA is a powerful multi-purpose Monte-Carlo code for particle transport and interactions with a broad range of applications. An overview of some program features will be given, as well as references for further information, followed by a practical exampel, which demonstrates how to construct a simple input.

Measurements on the MAX Injector System in Preparation for FEL Operation