W.F.J. Müller

GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Hesse, Germany

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Publications (98)152.17 Total impact

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    ABSTRACT: The first three-dimensional simulation study of thin multi-line readout cables using finite element simulation tool RAPHAEL is being reported. The application is the Silicon Tracking System (STS) of the fixed-target heavy-ion experiment Compressed Baryonic Matter (CBM), under design at the forthcoming accelerator center FAIR in Germany. RAPHAEL has been used to design low-mass analog readout cables with minimum possible Equivalent Noise Charge (ENC). Various trace geometries and trace materials have been explored in detail for this optimization study. These cables will bridge the distance between the microstrip detectors and the signal processing electronics placed at the periphery of the silicon tracking stations. SPICE modeling has been implemented in Sentaurus Device to study the transmission loss (dB loss) in cables and simulation has been validated with measurements. An optimized design having minimum possible ENC, material budget and transmission loss for the readout cables has been proposed.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2014; · 1.14 Impact Factor
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    ABSTRACT: The layout of the CBM Silicon Tracking System fore-sees the application of double-sided microstrip sensors in three sizes. All sensors have the same width of 6.2 cm, matching the width of the detector ladders that build up the tracking stations, and are segmented into 1024 strips of 58 µm pitch. The sensor heights, essentially correspond-ing to the strip lengths, are 6.2, 4.2 and 2.2 cm, depending on the position of the sensors within the tracking stations. Sensors close to the beam line, which are exposed to the highest track densities, have the shortest strip length. To-wards the periphery of the STS, sensors with longer strips, even daisy-chained sensors can be used still yielding small enough particle hit occupancies for efficient pattern recog-nition. A first series of silicon microstrip sensors in all three sizes has been designed in 2012. Their profiles are shown in Fig. 1. The projects, conducted in close cooper-ation of GSI (CBM05, CBM05H4) and JINR (CBM05H2s) complement the previous prototyping activities [1] in terms of design optimization towards the emerging silicon detec-tor module structure, and high production yield. They will yield tested pre-series prototypes in 2013.
    Scientific Report 2012 GSI Report 2013-1, (2013). 07/2013;
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    ABSTRACT: A new transition radiation detector (TRD) prototype foreseen to fulfill the requirements of the TRD subdetector of the CBM experiment at FAIR has been designed, constructed and tested with electrons and pions of a few GeV/c. The detector prototype was build with the original TRD architecture which preserves the high conversion efficiency of transition radiation in a single TRD layer. This TRD architecture is based on two multiwire proportional chambers readout by a common double-sided pad read-out electrode. The triangular shape of the readout pads gives access to the position information in both coordinates which defines the readout electrode plane. Pion efficiency as a function of number of TRD layers and position resolution were studied using electron and pion beams delivered by PS at CERN. Dedicated front-end electronics, designed for high counting rate environment was used. An extrapolated pion efficiency of 0.5% for a six layer TRD configuration at 90% electron efficiency using a regular foil radiator was obtained. The position resolution across the pads is of the order of 320μm and along the pads of 5.5 mm.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2013; 714:17–23. · 1.14 Impact Factor
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    ABSTRACT: In January 2012, a prototype setup of the Silicon Track-ing System (STS) for the CBM Experiment has been tested in a 2.4 GeV/c proton beam at the COSY synchrotron of Research Center Jülich, Germany. The experiment aimed at a full-sytem test of prototype detector stations, data ac-quisition system, detector controls and online monitoring. Hit and cluster finding algorithms were applied to evaluate the performance of neutron-irradiated prototype sensors. A simple track reconstruction algorithm was applied to the data acquired to determine the position resolution of the system.
    Scientific Report GSI 2013-1. 05/2013;
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    ABSTRACT: The Compressed Baryonic Matter (CBM) experiment will operate a free streaming data acquisition system. In order to optimize the data bandwidth and to achieve high performance, a data pre-processing is designed in the readout chain for the CBM-TOF detector. In this paper, we present the design of this module, results of its simulations and preliminary in-beam results which obtained with a test setup on the proton beam at the COSY accelerator in Jülich, Germany.
    Journal of Instrumentation 02/2013; 8(02):P02002. · 1.66 Impact Factor
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    Nuclear Physics A 01/2013; 904-905:1059. · 1.53 Impact Factor
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    S. Chatterji, M. Singla, W. F. J. Mueller, J. M. Heuser
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    ABSTRACT: This paper reports on the design optimization done for Double Sided silicon microStrip Detectors(DSSDs) to reduce the Equivalent Noise Charge (ENC) and to maximize the breakdown voltage and Charge Collection Efficiency. Various isolation techniques have been explored and a detailed comparison has been studied to optimize the detector performance. For the evaluation of the performance of the silicon detectors, a radiation damage model has been included. The neutron fluence is expected to be 2x10^{13}n_{eq} cm$^{-2}$ per year for five years of expected CBM run with intermediate periods of warm maintenance, cold maintenance and shutdown. Transient simulations have been performed to estimate the charge collection performance of the irradiated detectors and simulations have been verified with experimental data.
    IEEE Transactions on Nuclear Science 11/2012; 60(3). · 1.22 Impact Factor
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    T Balog, W F J Mueller, C J Schmidt
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    ABSTRACT: For detectors of the CBM experiment, high-rate, low-power and low-noise readout ASICs are needed. Since the Poisson distributed collisions between the nuclei are not correlated to a global trigger signal, the readout ASICs for both detectors as well as the data acquisition system itself must be self-triggered. The n-XYTER chip was developed for neutron exper-iments and nowadays it is also used for early prototyp-ing of the CBM detectors [1]. The performance of such a self-triggered front-end electronics has been studied last year [2]. The SPADIC chip [3] has been designed for the readout of the CBM transition radiation detectors. n-XYTER and SPADIC chips Their main difference is in the data storing and order-ing mechanism. The n-XYTER chip applies a Token Ring while the SPADIC chip uses an ordering FIFO to aggregate data from all channels into a single output. The Token Ring loops over all channels and if there is any data in a chan-nel FIFO the it reads it in and continues in the next period from next channel. Data do not come out time ordered and time re-sorting is needed at a later stage. This disadvantage is supposed to be eliminated by an ordering FIFO in the SPADIC chip. When a channel carries a signal it is (if pos-sible) stored in the channel FIFO and at the same moment there is an input information sent to the ordering FIFO. The FIFO is checked at each time period and the channels are read-out according to the information from this particular FIFO. Such a reading can lead to unexpected higher losses in the SPADIC chip and its performance has to be simu-lated therefore.
    Scientific Report 2011 GSI Report 2012-1. 05/2012;
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    ABSTRACT: The performance of the LAND neutron detector is studied. Using an event-mixing technique based on one-neutron data obtained in the S107 experiment at the GSI laboratory, we test the efficiency of various analytic tools used to determine the multiplicity and kinematic properties of detected neutrons. A new algorithm developed recently for recognizing neutron showers from spectator decays in the ALADIN experiment S254 is described in detail. Its performance is assessed in comparison with other methods. The properties of the observed neutron events are used to estimate the detection efficiency of LAND in this experiment.
    Nuclear Instruments and Methods in Physics Research A. 03/2012; 694:47.
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    ABSTRACT: The performance of Double Sided silicon Strip Detectors (DSSDs) and Kapton cables for the Silicon Tracking System (STS) of the upcoming Compressed Baryonic Matter (CBM) experiment at FAIR is being reported. The CBM STS will consist of 8 stations of DSSDs at a distance between 25–100 cm downstream of the target. These DSSDs have a pitch of around 58 µm, stereo angle of ± 7.50 with double metallization on either side. Total integrated fluence is expected to reach 1×1015 neq cm−2 for some of the STS stations. We present the first 3-D TCAD simulated results on DSSDs using tools from SYNOPSYS. To determine the radiation hardness of these sensors, we have irradiated some of the prototypes at KRI Cyclotron facility. Our radiation damage model implemented in TCAD simulations is able to reproduce the irradiated data. Besides the static characteristics, we have also extracted interstrip parameters relevant to understand strip isolation and cross-talk issues. Transient simulations have been performed to estimate the charge collection of irradiated sensors and the collected charge has been found to exactly mimic the variation of interstrip resistance with bias voltage. Also parameters relevant for noise calculations like metal trace resistance have been measured. For ENC calculations, it is also important to determine the contribution of analog kapton cables since the length of cables could reach up to 50 cm for inner modules. We present the first finite element simulations to extract the capacitive and series resistive noise contribution from kapton cables using RAPHAEL. In order to validate RAPHAEL, we have reproduced the D0 kapton simulations which were done using ANSYS. Present prototype kapton cables have been produced at Kharkov using Aluminum traces. This paper presents a detailed comparison between Aluminum and Copper traces in terms of noise and material budget. Copper seems to be better candidate for metal traces in cables.
    01/2011;
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    Nuclear Physics A 10/2009; 830:942-944. · 1.53 Impact Factor
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    ABSTRACT: Recently, is has been observed that events with the {\it same} total transverse energy of light charged particles (LCP) in the quasi target region, $E_{\perp 12}^{QT}$, show two quite distinct reaction scenarios in the projectile domain: multifragmentation and residue production. This phenomenon has been dubbed "bimodality". Using Quantum Molecular Dynamics calculations we demonstrate that this observation is very general. It appears in collisions of all symmetric systems larger than Ca and at beam energies between 50 A.MeV and 600 A.MeV and is due to large fluctuations of the impact parameter for a given $E_{\perp 12}^{QT}$. Investigating in detail the $E_{\perp 12}^{QT}$ bin in which both scenarios are present, we find that neither the average fragment momenta nor the average transverse and longitudinal energies of fragments show the behavior expected from a system in statistical equilibrium, in experiment as well as in QMD simulations. On the contrary, the experimental as well as the theoretical results point towards a fast process. This observation questions the conjecture that the observed bimodality is due to the coexistence of 2 phases at a given temperature in finite systems. Comment: accepted PRC
    Physical Review C 09/2009; · 3.72 Impact Factor
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    ABSTRACT: Isotopic effects in projectile fragmentation at relativistic energies have been studied with the ALADIN forward spectrometer at SIS. Stable and radioactive Sn and La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z ratio of the produced spectator sources, consistent with predictions for expanded systems. Consequences for the proposed interpretation of chemical breakup temperatures as representing the limiting temperatures predicted by microscopic models are discussed. Comment: 7 pages, 4 figures, contribution to proceedings of International School of Nuclear Physics, 30th Course, Heavy-Ion Collisions from the Coulomb Barrier to the Quark-Gluon Plasma, Erice-Sicily: 16 - 24 September 2008
    07/2009;
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    ABSTRACT: The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of (124)Sn and radioactive beams of (124)La and (107)Sn at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects (DeltaT approximately 0.6 MeV) appear for residue production near the onset of multifragmentation.
    Physical Review Letters 05/2009; 102(15):152701. · 7.73 Impact Factor
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    ABSTRACT: The discriminant-analysis method has been applied to optimize the exotic-beam charge recognition in a projectile fragmentation experiment. The experiment was carried out at the GSI using the fragment separator (FRS) to produce and select the relativistic secondary beams, and the ALADIN setup to measure their fragmentation products following collisions with Sn target nuclei. The beams of neutron poor isotopes around 124La and 107Sn were selected to study the isospin dependence of the limiting temperature of heavy nuclei by comparing with results for stable 124Sn projectiles. A dedicated detector to measure the projectile charge upstream of the reaction target was not used, and alternative methods had to be developed. The presented method, based on the multivariate discriminant analysis, allowed to increase the efficacy of charge recognition up to about 90%, which was about 20% more than achieved with the simple scalar methods. Comment: 6 pages, 7 eps figures, elsart, submitted to Nucl. Instr. and Meth. A
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 03/2008; · 1.14 Impact Factor
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    ABSTRACT: The spallation of 56Fe in collisions with hydrogen at 1A GeV has been studied in inverse kinematics with the large-aperture setup SPALADIN at GSI. Coincidences of residues with low-center-of-mass kinetic energy light particles and fragments have been measured allowing the decomposition of the total reaction cross section into the different possible deexcitation channels. Detailed information on the evolution of these deexcitation channels with excitation energy has also been obtained. The comparison of the data with predictions of several deexcitation models coupled to the INCL4 intranuclear cascade model shows that only GEMINI can reasonably account for the bulk of collected results, indicating that in a light system with no compression and little angular momentum, multifragmentation might not be necessary to explain the data.
    Physical Review Letters 02/2008; 100(2):022701. · 7.73 Impact Factor
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    ABSTRACT: Correlation functions, constructed from directional projections of the relative velocities of fragments, are used to determine the shape of the breakup volume in coordinate space. For central collisions of 129Xe + natSn at 50 MeV per nucleon incident energy, measured with the 4pi multi-detector INDRA at GSI, a prolate shape aligned along the beam direction with an axis ratio of 1:0.7 is deduced. The sensitivity of the method is discussed in comparison with conventional fragment-fragment velocity correlations.
    Physics Letters B 01/2008; 659(4):807. · 4.57 Impact Factor
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    ABSTRACT: Modern high energy physics experiments have to process terabytes of input data produced in particle collisions. The core of many data reconstruction algorithms in high energy physics is the Kalman filter. Therefore, the speed of Kalman filter based algorithms is of crucial importance in on-line data processing. This is especially true for the combinatorial track finding stage where the Kalman filter based track fit is used very intensively. Therefore, developing fast reconstruction algorithms, which use maximum available power of processors, is important, in particular for the initial selection of events which carry signals of interesting physics.One of such powerful feature supported by almost all up-to-date PC processors is a SIMD instruction set, which allows packing several data items in one register and to operate on all of them, thus achieving more operations per clock cycle. The novel Cell processor extends the parallelization further by combining a general-purpose PowerPC processor core with eight streamlined coprocessing elements which greatly accelerate vector processing applications.In the investigation described here, after a significant memory optimization and a comprehensive numerical analysis, the Kalman filter based track fitting algorithm of the CBM experiment has been vectorized using inline operator overloading. Thus the algorithm continues to be flexible with respect to any CPU family used for data reconstruction.Because of all these changes the SIMDized Kalman filter based track fitting algorithm takes 1 μs per track that is 10000 times faster than the initial version. Porting the algorithm to a Cell Blade computer gives another factor of 10 of the speedup.Finally, we compare performance of the tracking algorithm running on three different CPU architectures: Intel Xeon, AMD Opteron and Cell Broadband Engine.
    Computer Physics Communications 01/2008; · 2.41 Impact Factor
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    ABSTRACT: The N/Z dependence of projectile fragmentation at relativistic energies has been studied in a recent experiment at the GSI laboratory with the ALADiN forward spectrometer coupled to the LAND neutron detector. Besides a primary beam of 124Sn, also secondary beams of 124La and 107Sn delivered by the FRS fragment separator have been used in order to extend the range of isotopic compositions of the produced spectator sources. With the achieved mass resolution of \Delta A/A \approx 1.5%, lighter isotopes with atomic numbers Z \le 10 are individually resolved. The presently ongoing analyses of the measured isotope yields focus on isoscaling and its relation to the properties of hot fragments at freeze-out and on the derivation of chemical freeze-out temperatures which are found to be independent of the isotopic composition of the studied systems. The latter result is at variance with the predictions for limiting temperatures as obtained with finite-temperature Hartree-Fock calculations.
    12/2007;

Publication Stats

2k Citations
152.17 Total Impact Points

Institutions

  • 1984–2009
    • GSI Helmholtzzentrum für Schwerionenforschung
      Darmstadt, Hesse, Germany
  • 2008
    • Joint Institute for Nuclear Research
      Dubno, Moskovskaya, Russia
  • 2006
    • Max Planck Institute for Nuclear Physics
      Heidelburg, Baden-Württemberg, Germany
  • 1992
    • Lawrence Berkeley National Laboratory
      • Nuclear Science Division
      Berkeley, CA, United States