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  • 1.
    Akram, Nadeem
    et al.
    Stockholm University, Faculty of Science, Department of Physics. COMSATS Institute of Information Technology, Pakistan.
    Zhang, Hongqiang
    Stockholm University, Faculty of Science, Department of Physics.
    Soroka, I. L.
    Stockholm University, Faculty of Science, Department of Physics.
    Trautmann, C.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Transmission of slow highly charged ions through rectangular nanocapillaries2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 132043-Article in journal (Refereed)
    Abstract [en]

    Transmission of slow highly charged ions through rectangular nanocapillaries in phlogopite mica is studied. The transmission profiles have rhombic pattern at tilt angles within the geometrical opening angle of the capillaries. The time evolution of ion transmission reveals certain features contributing to the tailored transmission profiles.

  • 2.
    Ardenfors, Oscar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dasu, Alexandru
    Kopeć, Mariusz
    Gudowska, Irena
    Stockholm University, Faculty of Science, Department of Physics.
    Modelling of a proton spot scanning system using MCNP62017In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 860, article id 012025Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to model the characteristics of a clinical proton spot scanning beam using Monte Carlo simulations with the code MCNP6. The proton beam was defined using parameters obtained from beam commissioning at the Skandion Clinic, Uppsala, Sweden. Simulations were evaluated against measurements for proton energies between 60 and 226 MeV with regard to range in water, lateral spot sizes in air and absorbed dose depth profiles in water. The model was also used to evaluate the experimental impact of lateral signal losses in an ionization chamber through simulations using different detector radii. Simulated and measured distal ranges agreed within 0.1 mm for R90 and R80 , and within 0.2 mm for R50 . The average absolute difference of all spot sizes was 0.1 mm. The average agreement of absorbed dose integrals and Bragg-peak heights was 0.9%. Lateral signal losses increased with incident proton energy with a maximum signal loss of 7% for 226 MeV protons. The good agreement between simulations and measurements supports the assumptions and parameters employed in the presented Monte Carlo model. The characteristics of the proton spot scanning beam were accurately reproduced and the model will prove useful in future studies on secondary neutrons.

  • 3.
    Böhm, Sebastian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Enulescu, Alexandru
    Fritioff, Tomas
    Stockholm University, Faculty of Science, Department of Physics.
    Orban, Istvan
    Stockholm University, Faculty of Science, Department of Physics.
    Tashenov, Stanislav
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    First results from the Stockholm Electron Beam Ion Trap2007In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 58, no 303, p. 303-306Article in journal (Refereed)
    Abstract [en]

    A new laboratory for highly charged ions is being built up at Stockholm university. An electron beam ion trap (EBIT) (3T magnet,≤30 keV electron beam) was installed. It is used for spectroscopic studies, precision mass measurements, electron ion collisions, and highlycharged ion surface studies. Here we report about a fast ion-extraction scheme from ebit and first results using a time-of-flight detection as well as a labview based operational system of ebit.

  • 4.
    Carney, Rebecca
    et al.
    Lawrence Berkeley National Laboratory, USA.
    Bouchard, Kris
    Calafiura, Paolo
    Clark, David
    Donofrio, David
    Garcia-Sciveres, Maurice
    Livezey, Jesse
    Neuromorphic Kalman filter implementation in IBM's TrueNorth2017In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 898, no 4, article id 042021Article in journal (Refereed)
    Abstract [en]

    Following the advent of a post-Moore’s law field of computation, novel architectures continue to emerge. With composite, multi-million connection neuromorphic chips like IBM’s TrueNorth, neural engineering has now become a feasible technology in this novel computing paradigm. High Energy Physics experiments are continuously exploring new methods of computation and data handling, including neuromorphic, to support the growing challenges of the field and be prepared for future commodity computing trends. This work details the first instance of a Kalman filter implementation in IBM’s neuromorphic architecture, TrueNorth, for both parallel and serial spike trains. The implementation is tested on multiple simulated systems and its performance is evaluated with respect to an equivalent non-spiking Kalman filter. The limits of the implementation are explored whilst varying the size of weight and threshold registers, the number of spikes used to encode a state, size of neuron block for spatial encoding, and neuron potential reset schemes.

  • 5.
    Chen, Tao
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Forsberg, Björn
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Alf
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Modeling electron and energy transfer processes in collisions between ions and Polycyclic Aromatic Hydrocarbon molecules2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 102015-Article in journal (Refereed)
    Abstract [en]

    In this work we study collisions between ions and Polycyclic Aromatic Hydrocarbons with the aid of a novel over-the-barrier model and well-established models for nuclear and electronic stopping processes.

  • 6.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Andler, Guillermo
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Brännholm, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Bäckström, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Halldén, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Hanstorp, Dag
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Leontein, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Liljeby, Leif
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Paal, Andras
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Rensfelt, Karl-Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    First results from the Double ElectroStatic Ion-Ring ExpEriment, DESIREE2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 092003-Article in journal (Refereed)
    Abstract [en]

    We have stored the first beams in one of the rings of the double electrostatic ion-storage ring, DESIREE at cryogenic and at room temperature conditions. At cryogenic operations the following parameters are found. Temperature; T= 13K, pressure; p <10(-13) mbar, initial number of stored ions; N > 10(7) and storage lifetime of a C-2(-) beam; tau = 450 S.

  • 7.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Rosén, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Reinhed, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Löfgren, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Brännholm, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Blom, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Björkhage, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Bäckström, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Leontein, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Hanstorp, D.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Liljeby, Leif
    Stockholm University, Faculty of Science, Department of Physics.
    Källberg, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Simonsson, Ansgar
    Stockholm University, Faculty of Science, Department of Physics.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Mannervik, Sven
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Rensfelt, Karl-Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Danared, Håkan
    Stockholm University, Faculty of Science, Department of Physics. European Spallation Source, Sweden.
    Paál, Andras
    Stockholm University, Faculty of Science, Department of Physics.
    Masuda, Masaharu
    Stockholm University, Faculty of Science, Department of Physics.
    Halldén, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Andler, Guillermo
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Källersjö, Gunnar
    Stockholm University, Faculty of Science, Department of Physics.
    Weimer, Jan
    Stockholm University, Faculty of Science, Department of Physics.
    Hansen, K.
    Hartman, H.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 012040-Article in journal (Refereed)
    Abstract [en]

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

  • 8.
    Golod, Taras
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Frederiksen, Henrik
    Krasnov, Vladimir M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nb-PtNi-Nb Josephson junctions made by 3D FIB nano-sculpturing2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 150, no 5, p. 052062-Article in journal (Refereed)
    Abstract [en]

    We use Focused Ion Beam (FIB) for fabrication of nano-scale Superconductor-Ferromagnet-Superconductor (SFS) Josephson junctions, aiming to achieve a uniform, mono-domain state in the F-layer within the junction. We employ a Pt1-xNix alloy, characterized by the perfect solubility of the two components, for obtaining a homogeneous diluted ferromagnet. We perform a systematic analysis of both chemical composition, and ferromagnetic properties of Pt1—xNix thin films for different Ni—concentrations. The nano-scale homogeneity of the Pt1—xNix films is confirmed by energy dispersive X-ray spectroscopy. The Curie temperature of Pt1—xNix films decreases in a non-linear manner with Ni concentration. We observe that the critical current density of NbPt1—xNixNb junctions decreases non-monotonously with increasing Ni-concentration: at x 30% it exhibits a minimum, which we attribute to switching into the π state as a function of Ni-concentration.

  • 9.
    Hobein, Matthias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Solders, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Suhonen, Markus
    Stockholm University, Faculty of Science, Department of Physics.
    Liu, Yuwen
    Kamalou, Omar
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Re-trapping and cooling of highly-charged2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 163, p. 012109-Article in journal (Refereed)
    Abstract [en]

    Presently, a trapping system for cooling highly-charged ions (HCI) is being set up at AlbaNova at Stockholm University. The experiment aims at production of low temperature (emittance) HCI at very low energy. HCI are extracted from the new Stockholm EBIT (S-EBIT) before evaporative cooling is applied in a Penning trap. In the future the cooled ions will be injected into the precision trap of the high-precision mass spectrometer SMILETRAP II. In first tests the emittance of trapped ions was measured and it was shown that highly and low-charged ions could be simultaneously stored

  • 10.
    Kastlander, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bargholtz, Christoph
    Stockholm University, Faculty of Science, Department of Physics.
    Batres-Estrada, G
    Stockholm University, Faculty of Science, Department of Physics.
    Behrooz, K
    Stockholm University, Faculty of Science, Department of Physics.
    Development of methods to use CdTe detectors in field measurements2006In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 41, p. 523-526Article in journal (Refereed)
    Abstract [en]

    We are currently investigating the possibility to use CdTe detectors for in situ determinations of radionuclide concentration in soil. Buried activity can be reliably determined by a comparison of the count rate in the photo peak and the region between the photo peak and Compton edge. However, the pulse-height spectrum from CdTe detectors is severely deteriorated, due to poor charge collection, in particular for high gamma-ray energies. Our efforts have, therefore, been concentrated on improving the peak to valley ratio for such detectors. A simple, non-discriminating, algorithm for the analysis of output from two amplifiers with different shaping times is described. By means of this algorithm the peak-tovalley ratio for a small planar CdTe detector is improved by more than a factor of six compared to the uncorrected ratio without loss of efficiency.

  • 11.
    Katterwe, Sven-Olof
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Krasnov, Vladimir M.
    Stockholm University, Faculty of Science, Department of Physics.
    Interaction between flux-flow and phonon resonances in small Bi-2212 mesa structures2010In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 234, no 4, p. 042016-Article in journal (Refereed)
    Abstract [en]

    Resonant phenomena are important for the use of intrinsic Josephson junction as THz-oscillators, due to the decreased linewidth of emitted radiation when biasing the junctions near a resonance. We perform a detailed study of flux-flow characteristics and phonon resonances in small Bi(Pb)2Sr2CaCu2O8+x mesa structures. Magnetic field dependence of flux-flow characteristics up to 17 T and temperature and magnetic field dependence of phonon resonances at temperatures from 2 K to 80 K and in fields up to 15 T are analyzed. A shift of the phonon resonances in the presence of external magnetic fields and an interaction between flux-flow and phonon resonances are observed.

  • 12. Kvashnina, K.
    et al.
    Butorin, S
    Cui, Daging
    Stockholm University, Faculty of Science, Department of Environmental Chemistry.
    Vegelius, J.
    Puranen, A
    Gens, R
    Glatzel, P.
    Electron transfer during selenium reduction by iron surfaces in aqueous solution: high resolution X-ray absorption study2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 190, no 012191, p. 1-4Article in journal (Refereed)
    Abstract [en]

    In several designs proposed by different countries, high-level radioactive waste will be disposed in a canister with a copper outer container and a cast iron or carbon steel insert. If the iron insert comes into contact with anoxic geological water, anaerobic corrosion could take place and release fission products such as 79Se to the biosphere. This paper present studies of  the long-term kinetics of selenate (SeO42-) in the presence of iron surface under anaerobic conditions  by Near Edge X-ray Absorption Spectroscopy (XANES). Substantial changes in the selenium oxidation state is found and discussed in details. We assume that such behaviour corresponds  to the electron transfer from iron to selenium, which couldn't take place on oxidized iron surface. When selenate was in contact with polish steel foil in groundwater solution, reduction of Se and formation of Se(II-)was found.  These findings suggest that depending of corroded or oxidised iron surface, the selenium mobility in nuclear waste disposal systems will be different.

  • 13.
    Larson, Åsa
    et al.
    Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, Stockholm.
    Brinne Roos, Johanna
    Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, Stockholm.
    Stenrup, Michael
    Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, Stockholm.
    Orel, Ann
    Department of Applied Science, University of California, Davis.
    Ion-pair formation in electron recombination with molecular ions2007In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 88, p. 012065-1-012065-8Article in journal (Refereed)
    Abstract [en]

    By studying ion-pair formation in electron recombination with molecular ions,fundamental knowledge on the molecular dynamics can be obtained. In order to study thesetypes of reactions, both the electron recombination as well as the dynamics all the way to theasymptotic limits must be well described. We have used the wave packet technique to studyion-pair formation in electron recombination with HeH+, HD+, H3+ and HF+. We here discusswhat will determine the general shape of the ion-pair cross section, the threshold effects, possibleinterference effects as well as the ratio of the cross sections of ion-pair formation to dissociativerecombination.

  • 14.
    Lidén, Göran
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Surakka, Jouni
    A mini-sampler for welding aerosol mounted in close vicinity of the mouth/nose2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 151, no 1, p. 012041-Article in journal (Refereed)
    Abstract [en]

    A small personal aerosol mini-sampler to be used inside modern welding visors has been developed. The main object of the mini-sampler has been to sample manganese. The sampler is based on commercially available 13 mm filter holders but modified to incorporate an inlet nozzle made of aluminium. The nominal flow rate of the mini-sampler is 0,75 l/min. The sampler is to be worn mounted on a headset, modified from professional microphone headsets. The headset mounting arrangement was accepted by the welders. The sampling bias of the mini sampler versus the IOM sampler depends on the coarseness of the sampled aerosol. At the lowest concentration ratio of the open-face 25 mm filter holder to the IOM sampler equal to 0,65, the bias of the mini sampler is approximately -26% versus the IOM. The RMS sampling bias of the mini sampler versus the IOM sampler for manganese is -4,6%. The inhalable fraction of welding aerosol mass consists only of 25-55% of welding fume. The rest of the mass is made up of spatter particles and grinding particles. For manganese generally more than 65% is found in the fume.

  • 15.
    Lindroth, Eva
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Argenti, Luca
    Stockholm University, Faculty of Science, Department of Physics.
    Bengtsson, Jakob
    Stockholm University, Faculty of Science, Department of Physics.
    Ferro, Fabrizio
    Stockholm University, Faculty of Science, Department of Physics.
    Genkin, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Selstø, Sølve
    Stockholm University, Faculty of Science, Department of Physics.
    The Structure Behind it All2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 194, p. 012001-Article in journal (Refereed)
    Abstract [en]

    The talk discussed collisions where the structure of the systems involved plays a decisive role for the outcome of the event. For many types of charge changing processes the presence of resonant states can change the probability for a certain reaction by orders of magnitude. One example of this is electron-ion recombination where the resonant states are doubly or even multiply excited states lying above the ionization threshold of the recombined ion. The concept of a resonant state is discussed with the help of a simple model. The influence of such states is then illustrated through a few examples where some different calculational methods are compared with experiments. Finally, the possibility to also obtain accurate spectroscopical information from a collisional process is discussed

  • 16.
    Motzkau, Holger
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Katterwe, Sven-Olof
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Krasnov, Vladimir M.
    Stockholm University, Faculty of Science, Department of Physics.
    Size-dependent transformation from triangular to rectangular fluxon lattice in Bi-2212 mesa structures2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 400, article id 052022Article in journal (Refereed)
    Abstract [en]

    We present a systematic study of the field and size dependencies of the static fluxon lattice configuration in Bi-2212 intrinsic Josephson junctions and investigate conditions needed for the formation of a rectangular fluxon lattice required for a high power flux-flow oscillator. We fabricate junctions of different sizes from Bi2Sr2CaCu2O8+x and Bi1.75Pb0.25Sr2CaCu2O8+xsingle crystals using the mesa technique and study the Fraunhofer-like modulation of the critical current with magnetic field. The modulation can be divided into three regions depending on the formed fluxon lattice. At low field, no periodic modulation and no ordered fluxon lattice is found. At intermediate fields, modulation with half-flux quantum periodicity due to a triangular lattice is seen. At high fields, the rectangular lattice gives integer flux quantum periodicity. We present these fields in dependence on the sample size and conclude that the transitions between the regions depend only on λJ(Jc) and occur at about 0.4 and 1.3 fluxons per λJ, respectively. These numbers are universal for the measured samples and are consistent with performed numerical simulations.

  • 17.
    Nagy, Sz
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Fritioff, T
    Stockholm University, Faculty of Science, Department of Physics.
    Bergström, I
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Blaum, K
    Stockholm University, Faculty of Science, Department of Physics.
    Suhonen, M
    Stockholm University, Faculty of Science, Department of Physics.
    Schuch, R
    Stockholm University, Faculty of Science, Department of Physics.
    High-precision mass measurements for fundamental applications using highly-charged ions with SMILETRAP2007In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 58, p. 109-112Article in journal (Refereed)
    Abstract [en]

    The Penning trap mass spectrometer SMILETRAP takes advantage of highly-charged ions for high-accuracy mass measurements. In this paper recent mass measurements on Li and Ca ions are presented and their impact on fundamental applications discussed, especially the need for accurate mass values of hydrogen-like and lithium-like ions in the evaluation of the electron g-factor measurements in highly-charged ions is emphasized. Such experiments aim to test bound state quantum electrodynamics. Here the ionic mass is a key ingredient, which can be the limiting factor for the final precision.

  • 18.
    Ohm, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Pauly, Thilo
    CERN.
    The software of the ATLAS beam pick-up based LHC monitoring system2010In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 219, no 1Article in journal (Refereed)
    Abstract [en]

    The ATLAS BPTX stations are comprised of electrostatic button pick-up detectors, located 175 m away along the beam pipe on both sides of ATLAS. The pick-ups are installed as a part of the LHC beam instrumentation and used by ATLAS for timing purposes. The signals from the ATLAS BPTX detectors are used both in the trigger system and for a stand-alone monitoring system for the LHC beams and timing signals. The monitoring software measures the phase between collisions and clock with high accuracy in order to guarantee a stable phase relationship for optimal signal sampling in the sub-detector front-end electronics. It also measures the properties of the individual bunches and the structure of the beams. In this paper, the BPTX monitoring software is described, its algorithms explained and a few example monitoring displays shown. In addition, results from the monitoring system during the first period of single beam running in September 2008 are presented.

  • 19.
    Orbán, Istvan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Böhm, Sebastian
    Stockholm University, Faculty of Science, Department of Physics.
    Fogle, Mickhael
    Paál, Andras
    Stockholm University, Faculty of Science, Department of Physics, The Manne Siegbahn Laboratory.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    A new method for detecting the contribution of high Rydberg states to electron-ion recombination2007In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 58, no 299, p. 299-302Article in journal (Refereed)
    Abstract [en]

    A position sensitive detector for measuring field ionized electrons in the fringe field of a dipole magnet is presented. The detector provides a means to study, in a state selective fashion, recombination into high Rydberg states and offers a new method to investigate recombination enhancement effects. Several experimental considerations and possibilities are discussed in the text.

  • 20.
    Rydh, Andreas
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Golod, Taras
    Stockholm University, Faculty of Science, Department of Physics.
    Krasnov, Vladimir M.
    Stockholm University, Faculty of Science, Department of Physics.
    Field- and current controlled switching between vortex states in a mesoscopic superconductor2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 153, no 1, p. 012027-Article in journal (Refereed)
    Abstract [en]

    We study the controllable manipulation of vortices in a mesoscopic, superconducting "island" of Nb, using an integrated Josephson junction as a field-sensitive vortex detector. The island, divided by a single Josephson junction and suspended by Nb microbridges, was fabricated from a Nb/P11-xNix/Nb tri-layer using a focused ion beam. We find that the system at select magnetic fields behaves as a vortex memory cell, where current pulses can be used to switch the vortex configuration between metastable states of distinctly different junction critical currents. Non-destructive read-out of a state is then easily done with an intermediate current. Furthermore, we show that the Josephson junction displays a strong magnetoresistive effect at current bias well above the junction critical current but below the onset of flux flow. This enables the junction to be used as a quantitative probe of magnetic field with better than single flux quantum resolution.

  • 21.
    Sandqvist, Aa
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bergman, P.
    Bernath, P.
    Frisk, U.
    Hjalmarson, Å.
    Larsson, B.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lindqvist, M.
    Olberg, M.
    Olofsson, A. O. H.
    Pagani, L.
    Odin spectral line observations of Sgr A and Sgr B2 at submm wavelengths and in the 118-GHz band2006In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 54, p. 72-76Article in journal (Refereed)
    Abstract [en]

    Since its launch in 2001, the Odin satellite has been observing the Galactic Centre Sgr A Complex (CND, +20 and +50 km s-1 Clouds) as well as the nearby star formation region, Sgr B2, a number of times. Observations have been made in the 118-119 GHz and 486-581 GHz bands. A limited mapping of the Sgr A Complex in the H162O line has been performed and new observations of the H182O line took place in 2006. In the 118-119 GHz band, a strong line of HC3N (J = 13 - 12) has been detected at a number of positions - sensitive upper limits have been obtained for the O2 (11 - 10) and the SiC (3Π2, J = 3 - 2) lines. Towards Sgr B2, submm observations have yielded absorption profles of H162O, H182O, H172O, NH3, and 15NH3.

  • 22.
    Tagliati, Stella
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Pipping, Jonathan
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Time-dependent simulations of a membrane-based nanocalorimeter2010In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 234, no 4, p. 042036-Article in journal (Refereed)
    Abstract [en]

    We present time-dependent numerical simulations of the thermal and electrical response of a membrane-based nanocalorimeter designed for general studies of heat capacity and latent heat of milligram to sub-microgram samples. The investigated device is based on freestanding, 150 nm thick silicon nitride membranes onto which thin film heaters and temperature sensors are fabricated. This design makes the thermal link small enough to allow both relaxation and ac steady-state methods to be used interchangeably. We compare simulations of the two-dimensional thermal behavior of the nanocalorimeter with the results of experiments. The simulations take current distribution, heat generation and heat flow into consideration, and shed light on the frequency dependent contribution of the membrane heat capacity in ac steady-state experiments. The simulations also illustrate where energy is stored, thus assisting further improvement of the device design.

  • 23.
    Tagliati, Stella
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Absolute specific heat measurements of a microgram Pb crystal using ac nanocalorimetry2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 400, no 022120Article in journal (Refereed)
    Abstract [en]

    Heat capacity measurements using the ac steady state method are often considered difficult to provide absolute accuracy. By adjusting the working frequency to maintain a constant phase and using the phase information to obtain the heat capacity, we have found that it is possible to achieve good absolute accuracy. Here we present a thermodynamic study of a ~2.6 μg Pb superconducting crystal to demonstrate the newly opened capabilities. The sample is measured using a differential membrane-based calorimeter. The custom-made calorimetric cell is a pile of thin film Ti heater, insulation layer and Ge1-xAux thermometer fabricated in the center of two Si3N4 membranes. It has a background heat capacity < 100 nJ/K at 300 K, decreasing to 9 pJ/K at 1 K. The sample is characterized at temperatures down to 0.5 K. The zero field transition at Tc = 7.21 K has a width ≈20 mK and displays no upturn in C. From the heat capacity jump at Tc and the extrapolated Sommerfeld term we find ΔC/γTc = 2.68. The latent heat curve obtained from the zero field heat capacity measurement, and the deviations of the thermodynamic critical field from the empirical expression Hc = Hc(0)[1-(T/Tc)2] are discussed. Both analyses give results in good agreement with literature.

  • 24.
    Tagliati, Stella
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Xie, R.
    Argonne National Laboratory, USA.
    Welp, U.
    Argonne National Laboratory, USA.
    Kwok, W. K.
    Argonne National Laboratory, USA.
    Membrane-based calorimetry for studies of sub-microgram samples2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 150, p. 052256-Article in journal (Refereed)
    Abstract [en]

    We have developed a membrane-based microcalorimeter for general measurements of heat capacity and latent heat using a combination of ac steady-state and relaxation methods. The differential calorimeter is designed for sub-microgram samples studied over a wide range of temperatures and magnetic fields. The device is based on free-standing silicon nitride membranes of 150 nm thickness onto which thin film heaters and temperature sensors are fabricated. While production-line fabrication may benefit from back-etching as a final step, it is often easier to start with pre-etched membranes in a research laboratory. With selected nano-fabrication methods this is possible. Due to a robust heater and very low thermal conductance of the final calorimeter, the sample can be heated to more than 100 K above base temperature. This enables instantaneous calibration, and makes the device capable of being used for ultra-fast temperature control, relaxation studies, and measurements that combine good absolute accuracy, high resolution, and information on latent heat.

  • 25.
    Valdes Santurio, Eduardo
    Stockholm University, Faculty of Science, Department of Physics.
    Upgrade of Tile Calorimeter of the ATLAS Detector for the High Luminosity LHC.2017In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 928, article id 012024Article in journal (Refereed)
    Abstract [en]

    The Tile Calorimeter (TileCal) is the hadronic calorimeter of ATLAS covering the central region of the ATLAS experiment. TileCal is a sampling calorimeter with steel as absorber and scintillators as active medium. The scintillators are read out by wavelength shifting fibers coupled to photomultiplier tubes (PMT). The analogue signals from the PMTs are amplified, shaped and digitized by sampling the signal every 25 ns. The High Luminosity Large Hadron Collider (HL-LHC) will have a peak luminosity of 5 × 1034 cm −2 s −1, five times higher than the design luminosity of the LHC. TileCal will undergo a major replacement of its on- and off-detector electronics for the high luminosity programme of the LHC in 2026. The calorimeter signals will be digitized and sent directly to the off-detector electronics, where the signals are reconstructed and shipped to the first level of trigger at a rate of 40 MHz. This will provide a better precision of the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. Three different options are presently being investigated for the front-end electronic upgrade. Extensive test beam studies will determine which option will be selected. Field Programmable Gate Arrays (FPGAs) are extensively used for the logic functions of the off- and on-detector electronics. One hybrid demonstrator prototype module with the new calorimeter module electronics, but still compatible with the present system, may be inserted in ATLAS at the end of 2016.

  • 26.
    Zettergren, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rousseau, P.
    Wang, Y.
    Seitz, Fabian
    Stockholm University, Faculty of Science, Department of Physics.
    Chen, Tao
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Alexander, John D.
    Stockholm University, Faculty of Science, Department of Physics.
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Rangama, J.
    Chesnel, J. Y.
    Capron, M.
    Poully, J. C.
    Domaracka, A.
    Mery, A.
    Maclot, S.
    Vizcaino, V.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Adoui, L.
    Alcami, M.
    Tielens, A. G. G. M.
    Martin, F.
    Huber, B. A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Bond formation in C-59(+)-C-60 collisions2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 012028-Article in journal (Refereed)
    Abstract [en]

    In this work, we show that keV-ions are able to remove single carbon atoms from individual fullerenes in clusters of C-60 molecules. This very efficiently leads to the formation of exotic q dumbbell molecules through secondary C-59(+) - C-60 collisions within the fragmenting cluster. Such molecular fusion processes are inherently different from those induced by photons where only products with even numbers of carbon atoms are observed. Thus, ion collisions ignite unique and hitherto overlooked secondary reactions in small aggregates of matter. This relates to the question on how complex molecules may form in e.g. space.

  • 27.
    Zhang, H. Q.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Lanzhou University, China.
    Akram, N.
    Stockholm University, Faculty of Science, Department of Physics.
    Soroka, I. L.
    Stockholm University, Faculty of Science, Department of Physics.
    Trautmann, C.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Transmission of highly charged ions through nanocapillaries of noncircular cross sections2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 488, p. 012035-Article in journal (Refereed)
    Abstract [en]

    We report on effects from the geometrical shape of the guiding channels on the ion transmission profile. We find that capillaries of rhombic cross section produce rectangular shaped ion transmission profiles and, vice versa, capillaries of rectangular geometry give a rhombic beam shape. Our trajectory simulations for the incidence of 14-keV Ne7+ ions give clear evidence that the observed effect is due to the image forces experienced by the transmitting ions. They gain transverse energy due the image charge attraction towards the inner surfaces of the capillary. This leads to a defocusing of the ions leaving the capillaries. Due to the blocking of large deflection angles at the exit of the capillary, the transmitted ion beam is tailored into certain geometrical patterns.

  • 28.
    Zhang, Hongqiang
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Skog, Patrik
    Stockholm University, Faculty of Science, Department of Physics.
    Schuch, Reinhold
    Stockholm University, Faculty of Science, Department of Physics.
    Guiding of slow highly charged ions through insulating nano-capillaries2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 163, no 1Article in journal (Refereed)
    Abstract [en]

    The guiding of highly charged ions through SiO2 nano-capillaries has been investigated by our group, using 7 keV Ne7+-ions. We studied in particular the transmission of ions incident at angles greater than the angle given by the capillary aspect ratio as a function of charge incident on the capillary membrane. In this report we show the re-arrangement of charge patches inside the capillary by observing the evolution of the two-dimensional angular distributions of the transmitted ions.

  • 29.
    Åman, Jan E.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Bedford, James
    Grumiller, Daniel
    Pidokrajt, Narit
    Stockholm University, Faculty of Science, Department of Physics.
    Ward, John
    Ruppeiner theory of black hole thermodynamics2007In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 66, p. 012007-Article in journal (Refereed)
    Abstract [en]

    The Ruppeiner metric as determined by the Hessian of the Gibbs surface provides a geometric description of thermodynamic systems in equilibrium. An interesting example is a black hole in equilibrium with its own Hawking radiation. In this article, we present results from the Ruppeiner study of various black hole families from different gravity theories e.g. 2D dilaton gravity, BTZ, general relativity and higher-dimensional Einstein-Maxwell gravity.

1 - 29 of 29
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