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We present a numerical investigation of energy and charge distributions during electron-beam-induced growth of tungsten nanostructures on SiO2 substrates by using a Monte Carlo simulation of the electron transport. This study gives a quantitative insight into the deposition of energy and charge in the substrate and in the already existing metallic nanostructures in the presence of the electron beam. We analyze electron trajectories, inelastic mean free paths, and the distribution of backscattered electrons in different compositions and at different depths of the deposit. We find that, while in the early stages of the nanostructure growth a significant fraction of electron trajectories still interacts with the substrate, when the nanostructure becomes thicker the transport takes place almost exclusively in the nanostructure. In particular, a larger deposit density leads to enhanced electron backscattering. This work shows how mesoscopic radiation-transport techniques can contribute to a model that addresses the multi-scale nature of the electron-beam-induced deposition (EBID) process. Furthermore, similar simulations can help to understand the role that is played by backscattered electrons and emitted secondary electrons in the change of structural properties of nanostructured materials during post-growth electron-beam treatments.
The elliptic, v2, triangular, v3, and quadrangular, v4, azimuthal anisotropic flow coefficients are measured for unidentified charged particles, pions, and (anti-)protons in Pb–Pb collisions at √sNN=2.76 TeV with the ALICE detector at the Large Hadron Collider. Results obtained with the event plane and four-particle cumulant methods are reported for the pseudo-rapidity range |η|<0.8 at different collision centralities and as a function of transverse momentum, pT, out to pT=20 GeV/c. The observed non-zero elliptic and triangular flow depends only weakly on transverse momentum for pT>8 GeV/c. The small pT dependence of the difference between elliptic flow results obtained from the event plane and four-particle cumulant methods suggests a common origin of flow fluctuations up to pT=8 GeV/c. The magnitude of the (anti-)proton elliptic and triangular flow is larger than that of pions out to at least pT=8 GeV/c indicating that the particle type dependence persists out to high pT.
The gauge principle is fundamental in formulating the Standard Model. Fermion–gauge-boson couplings are the inescapable consequence and the primary determining factor for observable phenomena. Vertices describing such couplings are simple in perturbation theory and yet the existence of strong-interaction bound-states guarantees that many phenomena within the Model are nonperturbative. It is therefore crucial to understand how dynamics dresses the vertices and thereby fundamentally alters the appearance of fermion–gauge-boson interactions. We consider the coupling of a dressed-fermion to an Abelian gauge boson, and describe a unified treatment and solution of the familiar longitudinal Ward–Green–Takahashi identity and its less well known transverse counterparts. Novel consequences for the dressed-fermion–gauge-boson vertex are exposed.
Previous experimental measurements from nuclear collisions have indicated modifications of jets by interaction with the medium created in the collision. Observables from particle correlations in the ALICE detector continue to provide access to key properties of the hot deconfined nuclear matter. New results from two- and three-particle number and transverse momentum correlations are discussed. Specifically, correlation function properties are characterized as a function of transverse momentum and centrality and for different charge combinations. Fourier decompositions are performed, identified particle ratios are studied in the jet-like peak and in the bulk, and the away-side shape is looked at in three-particle correlations.
The ALICE detector is ideally suited to study the production of anti- and hyper-matter due to its excellent particle identification capabilities. The measurement of the He¯4-nucleus in Pb–Pb collisons at sNN=2.76TeV is presented. We further show the performance for the reconstruction of the (anti-)hypertriton in the decay to He3+π− (He¯3+π+). In addition to this, two searches have been performed, one for the H-Dibaryon →Λpπ− and one for the Λn bound state (Λn¯→d¯π+). No signals are observed for these exotic states and upper limits have been determined.
In high-energy nuclear collisions, heavy quark potential at finite temperature controls the quarkonium suppression. Including the relaxation of the medium induced by the relative velocity between quarkonia and the deconfined expanding matter, the Debye screening is reduced and the quarkonium dissociation takes place at a higher temperature. As a consequence of the velocity-dependent dissociation temperature, the quarkonium suppression at high transverse momentum is significantly weakened in high-energy nuclear collisions at RHIC and LHC.
We investigate the modification of the pion self-energy at finite temperature due to its interaction with a low-density, isospin-symmetric nuclear medium embedded in a constant magnetic background. To one loop, for fixed temperature and density, we find that the pion effective mass increases with the magnetic field. For the π−, interestingly, this happens solely due to the trivial Landau quantization shift ∼|eB|, since the real part of the self-energy is negative in this case. In a scenario in which other charged particle species are present and undergo an analogous trivial shift, the relevant behavior of the effective mass might be determined essentially by the real part of the self-energy. In this case, we find that the pion mass decreases by ∼10% for a magnetic field |eB|∼mπ2, which favors pion condensation at high density and low temperatures.
The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y|<0.8) in the transverse momentum range 1<pT<8 GeV/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy √s=7 TeV using an integrated luminosity of 2.2 nb−1. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark–antiquark pairs.
The inclusive transverse momentum (pT) distributions of primary charged particles are measured in the pseudo-rapidity range |η|<0.8 as a function of event centrality in Pb–Pb collisions at √sNN=2.76 TeV with ALICE at the LHC. The data are presented in the pT range 0.15<pT<50 GeV/c for nine centrality intervals from 70–80% to 0–5%. The results in Pb–Pb are presented in terms of the nuclear modification factor RAA using a pp reference spectrum measured at the same collision energy. We observe that the suppression of high-pT particles strongly depends on event centrality. The yield is most suppressed in central collisions (0–5%) with RAA≈0.13 at pT=6–7 GeV/c. Above pT=7 GeV/c, there is a significant rise in the nuclear modification factor, which reaches RAA≈0.4 for pT>30 GeV/c. In peripheral collisions (70–80%), only moderate suppression (RAA=0.6–0.7) and a weak pT dependence is observed. The measured nuclear modification factors are compared to other measurements and model calculations.
Long-range angular correlations on the near and away side in p–Pb collisions at √sNN=5.02 TeV
(2013)
Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5<pT,assoc<pT,trig<4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and pT bins, and the widths show no significant evolution with event multiplicity or pT. These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge.
We investigate the phase structure of strongly interacting matter at non-vanishing isospin before the onset of pion condensation in the framework of the unquenched Polyakov–Quark-Meson model with 2+1 quark flavors. We show results for the order parameters and all relevant thermodynamic quantities. In particular, we obtain a moderate change of the pressure with isospin at vanishing baryon chemical potential, whereas the chiral condensate decreases more appreciably. We compare the effective model to recent lattice data for the decrease of the pseudo-critical temperature with the isospin chemical potential. We also demonstrate the major role played by the value of the pion mass in the curvature of the transition line, and the need for lattice results with a physical pion mass. Limitations of the model at nonzero chemical potential are also discussed.
The width of the ω meson in cold nuclear matter is computed in a hadronic many-body approach, focusing on a detailed treatment of the medium modifications of intermediate πρ states. The π and ρ propagators are dressed by their self-energies in nuclear matter taken from previously constrained many-body calculations. The pion self-energy includes Nh and Δh excitations with short-range correlations, while the ρ self-energy incorporates the same dressing of its 2π cloud with a full 3-momentum dependence and vertex corrections, as well as direct resonance-hole excitations; both contributions were quantitatively fit to total photo-absorption spectra and πN→ρN scattering. Our calculations account for in-medium decays of type ωN→πN(⁎),ππN(Δ), and 2-body absorptions ωNN→NN(⁎),πNN. This causes deviations of the in-medium ω width from a linear behavior in density, with important contributions from spacelike ρ propagators. The ω width from the ρπ cloud may reach up to 200 MeV at normal nuclear matter density, with a moderate 3-momentum dependence. This largely resolves the discrepancy of linear T–ϱ approximations with the values deduced from nuclear photoproduction measurements.
Problems of production and study of new neutron-enriched heavy nuclei are discussed. Low-energy multinucleon transfer reactions are shown to be quite appropriate for this purpose. Reactions with actinide beams and targets are of special interest for synthesis of new neutron-enriched transfermium nuclei and not-yet-known nuclei with closed neutron shell N = 126 having the largest impact on the astrophysical r-process. The estimated cross sections for the production of these nuclei look very promising for planning such experiments at currently available accelerators. These experiments, however, are rather expensive and difficult to perform because of low intensities of the massive projectile beams and problems of separating and detecting the heavy reaction products. Thus, realistic predictions of the corresponding cross sections for different projectile-target combinations are definitely required. Some uncertainty still remains in the values of several parameters used for describing the low-energy nuclear dynamics. This uncertainty does not allow one to perform very accurate predictions for the productions of new heavier-than-target (trans-target) nuclei in multinucle on transfer reactions. Nevertheless these predictions are rather promising (large cross sections) to start such experiments at available accelerators if the problem of separation of heavy transfer reaction products would be solved.
Above 1 MeV of incident neutron energy the fission fragment angular distribution (FFAD) has generally a strong anisotropic behavior due to the combination of the incident orbital momentum and the intrinsic spin of the fissioning nucleus. This effect has to be taken into account for the efficiency estimation of devices used for fission cross section measurements. In addition it bears information on the spin deposition mechanism and on the structure of transitional states. We designed and constructed a detection device, based on Parallel Plate Avalanche Counters (PPAC), for measuring the fission fragment angular distributions of several isotopes, in particular 232Th. The measurement has been performed at n_TOF at CERN taking advantage of the very broad energy spectrum of the neutron beam. Fission events were recognized by back to back detection in coincidence in two position-sensitive detectors surrounding the targets. The detection efficiency, depending mostly on the stopping of fission fragments in backings and electrodes, has been computed with a Geant4 simulation and validated by the comparison to the measured case of 235U below 3 keV where the emission is isotropic. In the case of 232Th, the result is in good agreement with previous data below 10 MeV, with a good reproduction of the structures associated to vibrational states and the opening of second chance fission. In the 14 MeV region our data are much more accurate than previous ones which are broadly scattered.
[Nachruf] Heinrich Rohrer
(2013)
We present the application of an evolutionary genetic algorithm for the in situ optimization of nanostructures that are prepared by focused electron-beam-induced deposition (FEBID). It allows us to tune the properties of the deposits towards the highest conductivity by using the time gradient of the measured in situ rate of change of conductance as the fitness parameter for the algorithm. The effectiveness of the procedure is presented for the precursor W(CO)6 as well as for post-treatment of Pt–C deposits, which were obtained by the dissociation of MeCpPt(Me)3. For W(CO)6-based structures an increase of conductivity by one order of magnitude can be achieved, whereas the effect for MeCpPt(Me)3 is largely suppressed. The presented technique can be applied to all beam-induced deposition processes and has great potential for a further optimization or tuning of parameters for nanostructures that are prepared by FEBID or related techniques.
This doctoral thesis is concerned with the development of a method that allows to measure in vivo and non-invasively the mid-infrared absorption spectra of human epidermis, using photoacoustic spectroscopy. The main focus is the monitoring of the glucose level in epidermal interstitial fluid and its correlation with the blood glucose level; which is the most important parameter for the diagnosis and treatment of diabetes mellitus. Most publications in this field have only reported measurements in vitro for the absorption spectra of epidermis in the mid-infrared range. Using the approach presented in this work, it was possible to record in vivo and in situ the absorption spectra of skin of volunteers; and with these spectra, the changing glucose concentration could be monitored. The novelty of the photoacoustic method introduced here is that it operates in acoustic resonance in the ultrasound range. This considerably reduces the signal noise due to the external acoustic background. Although the photoacoustic method reported in this work was used to measure glucose in human epidermis, it can also be applied to other solid samples with relevant absorption bands in the mid-infrared. Furthermore, it can be used in other spectral regions if the laser source covers relevant absorption bands of the sample.
In Chinese medicine acupuncture points are treated by physical stimuli to counteract various diseases. These stimuli include mechanical stress as applied during the needle manipulation or tuina, high temperatures as applied during moxibustion, and red laser light applied during laser acupuncture. This study aimed to investigate cellular responses to stimuli that might occur in the tissue of acupuncture points. Since they have a characteristically high density of mast cells that degranulate in response to acupuncture, we asked whether these processes lead to ATP release. We tested in in vitro experiments on mast cells of the human mast-cell line HMC-1 the effects of the physical stimuli; mechanical stress was applied by superfusion of the cells with hypotonic solution, heat was applied by incubation of the cells at 52°C, and red laser light of 657 nm was used for irradiation. We demonstrate that all the stimuli induce ATP release from model human mast HMC-1 cells, and this release is associated with an intracellular free Ca2+ rise. We hypothesize that ATP released from mast cells supplements the already known release of ATP from keratinocytes and, by acting on P2X receptors, it may serve as initial mediator of acupuncture-induced analgesia.
The conducting properties in the basal ab plane of pure and Al-doped YBa2Cu3O7-γ single crystals before and after long-time exposure in air atmosphere are investigated. It is shown that prolonged aging leads to an increase of the density of effective scattering centers for the normal carriers. The aluminum doping has been revealed to partially slowdown the degradation of the conducting properties in process of aging. The excess conductivity, Δδ(T), has been found to obey exponential dependence in the broad temperature range Tc<T<T*. In the pseudogap regime, the mean-field transition temperature and the 3D-2D crossover point in the excess conductivity have been quantified. Near the critical temperature, is described well within the Aslamazov-Larkin theoretical model. Herewith, both aluminum doping and prolonged aging have been found to essentially expand the temperature interval of implementation of the pseudogap state, thus narrowing the linear section in the dependence ρab(T).
The physics of EPOS
(2013)
Die Druckmessung in Tieftemperatur-Vakuumsystemen stellt ein großes messtechnisches Problem dar. Für die in solchen Systemen auftretenden Drücke im UHV und XHV-Bereich werden meist Ionisationsmanometer vom Glühkathodentyp zur Druckmessung verwendet. Diese haben jedoch den entscheidenden Nachteil, dass durch die Verwendung einer Glühkathode zur Erzeugung freier Elektronen eine große Wärmelast in das System eingekoppelt wird. Dies führt zu einer Störung des thermischen Gleichgewichts und damit zu einer Verfälschung der Druckmessung. Weiterhin muss diese zusätzliche Wärmelast abgeführt werden, was vor allem bei kryogenen Vakuumsystemen einen erheblichen Mehraufwand darstellt.
Um dieses Problem zu umgehen, wurde ein Ionisationsmanometer entwickelt, dessen Glühkathode durch eine kalte Elektronenquelle ersetzt wurde. Der verwendete Feldemitter, eine kommerziell erhältliche CNT-Kathode, wurde gegenüber dem Anodengitter einer Extraktormessröhre positioniert. Mit diesem Aufbau wurden die Charakteristika von Kathode und Messröhre sowohl bei Raumtemperatur als auch unter kryogenen Vakuumbedingungen untersucht.
Dabei konnte gezeigt werden, dass die modifizierte Messröhre auch bei einer Umgebungstemperatur von 6 K ohne funktionale Einbußen betrieben werden kann und der gemessene Ionenstrom über mehrere Dekaden linear mit dem von einer Extraktormessröhre mit Glühkathode gemessenen Referenzdruck ansteigt. Des Weiteren konnte gezeigt werden, dass der Extraktor mit CNT-Kathode unter diesen kryogenen Bedingungen deutlich sensitiver auf geringe Druckschwankungen reagiert als sein Äquivalent mit Glühkathode.
In this work the main emphasis is put on the investigation of relativistic shock waves and Mach cones in hot and dense matter using the microscopic transport model BAMPS, based on the relativistic Boltzmann equation. Using this kinetic approach we study the complete transition from ideal-fluid behavior to free streaming. This includes shock-wave formation in a simplified (1+1)-dimensional setup as well as the investigation of Mach-cone formation induced by supersonic projectiles and/or jets in (2+1)- and (3+1)-dimensional static and expanding systems. We further address the question whether jet-medium interactions inducing Mach cones can contribute to a double-peak structure observed in two-particle correlations in heavy-ion collision experiments. Furthermore, BAMPS is used as a benchmark to compare kinetic theory to several relativistic hydrodynamic theories in order to verify their accuracy and to find their limitations.
Using a partonic transport model we investigate the evolution of conical structures in ultrarelativistic matter. Using two different source terms and varying the transport properties of the matter we study the formation of Mach Cones. Furthermore, in an additional study we extract the two-particle correlations from the numerical calculations and compare them to an analytical approximation. The influence of the viscosity to the shape of Mach Cones and the corresponding two-particle correlations is studied by adjusting the cross section of the medium.
Bei der Ionenstrahltherapie bestimmt die Energie der Ionen die Eindringtiefe in das Gewebe und damit die Lage des Braggpeaks, in dem der größte Teil der Ionisationsenergie deponiert wird.
Um die gewünschte Dosis möglichst genau im Tumor zu lokalisieren, müssen in den aufeinanderfolgenden Extraktionen die gewünschten unterschiedlichen Energien möglichst genau sein.
In der Beschleunigungsphase werden die Magnetfelder der Magnete im Synchrotron bis zum vorgegebenen Exktraktionswert hochgefahren. Dieser bestimmt zusammen mit der Synchrotronfrequenz die Strahlenergie. Während und insbesondere am Ende dieser Phase, Rampe genannt, sollte das Magnetfeld daher sehr genau dem berechneten Sollwert folgen, um Strahlverluste zu minimieren und die geforderte Strahlqualität zu erreichen.
In der zeitlichen Steuerung der Magnetströme müssen magnetische Effekte, die hauptsächlich im Eisen der Magnete auftreten, wie Wirbelströme und die Hysterese berücksichtigt werden, da sie das Feld verfälschen und damit den Strahl in unerwünschter Weise beeinflussen. Die während der Rampe entstehenden Wirbelströme stören das Magnetfeld, so dass bisher vor der Extraktion des Strahls eine Wartezeit eingeführt wurde, bis die Wirbelströme abgeklungen waren.
Bei beliebig wählbaren Abfolgen der vordefinierten Zyklen kommt es durch die Hysterese des Eisens zu unterschiedlichen Remanenzfeldern, die das Magnetfeld verändern. Um dem vorzubeugen, durchliefen die Magnete eine vordefinierte Hystereseschleife. Ist die geforderte Energie des Strahls erreicht, wird das Magnetfeld konstant gehalten und die Teilchen aus dem Synchrotron extrahiert. Der Rest der Hystereseschleife wurde am Ende des Zyklus durchlaufen.
Die im Rahmen dieser Dissertation entwickelte dynamische Magnetfeldregelung misst das integrale Magnetfeld sehr genau und korrigiert die Feldfehler. Das integrale Magnetfeld folgt damit jederzeit seiner Vorgabe, unabhängig von den dynamischen Störeffekten. Die Wirbelströme und die Hysterese sind zwar immer noch vorhanden, die dadurch verursachten Feldfehler können aber durch eine Rückkopplung auf den Strom des Magneten korrigiert werden.
Es werden verschiedene Verfahren zur Messung der Magnetfelder untersucht. Am besten eignet sich für die dynamische Magnetfeldregelung die Kombination aus einer Hallsonden- und einer Induktionsspulenmessung. Die Messung muss das integrale Magnetfeld des Magneten BL, also das gesamte Feld entlang des Strahlwegs, bestimmen. Die Induktionsspule, oder Pickupspule, liegt deshalb entlang des Strahlrohrs im Magneten und liefert eine Spannung in Abhängigkeit von der Änderung des magnetischen Flusses. Durch die Integration dieser Spannung erhält man das integrale Feld des Magneten. Die Messung wird mit einer Hallsondenmessung zu Beginn des Beschleunigerzyklus auf einen absoluten Messwert geeicht.
Der Hauptteil dieser Arbeit beschäftigt sich mit der Entwicklung des sogenannten HIT Integrators, der die Integration der Pickupspulenspannung übernimmt. Bisher verfügbare Integratoren konnten die notwendigen Anforderungen an Genauigkeit, Echtzeitfähigkeit, automatische Kalibrierung, ständige Messbereitschaft, Temperaturunabhängigkeit und hohe Verfügbarkeit nicht erfüllen. Der neu entwickelte HIT Integrator wurde diesen Anforderungen entsprechend entwickelt. Der Integrator mit dem neuartigen Konzept der gleichzeitigen Messung und Kalibrierung in Echtzeit ist als Patent angemeldet worden. Neben der Entwicklung und Verwirklichung des Gesamtkonzepts war die numerische Integration des stark verrauschten Pickupspulensignals und die sofortige Umsetzung des integralen Werts in ein Steuersignal für die Dipolmagnetstromgeräte eine besondere technische Herausforderung.
Die elektronischen Schaltungen für die dynamische Magnetfeldregelung sind in der Baugruppe des HIT Integrators zusammengefasst. Die Ansteuerung der Hallsonde mit einer temperaturkompensierten Stromquelle, der Signalaufbereitung und Analog-Digital-Wandlung, sowie der Integrator und der Regler bilden eine technische Einheit.
Der HIT Integrator ist speziell für den Einsatz im bestehenden Beschleunigerkontrollsystem und den Magnetnetzgeräten entwickelt worden.
Die Regler der Magnetnetzgeräte wurden so verändert, dass sie einen Zusatzsollwert verarbeiten können, der auf den berechneten Sollwert der Datenversorgung addiert wird.
Die Magnetfeldregelung wurde in den Therapiebeschleuniger integriert, dazu wurde die Datenversorgung und das Kontrollsystem angepasst. Die Magnetfeldregelung stellt ein neues Gerät im Beschleuniger dar, das in die Netzgeräte der Synchrotronmagnete eingebaut worden ist. Die Datenversorgung dieser Geräte beinhaltet u.a. eine neue Methode der Kalibrierung.
Es konnte durch Messungen gezeigt werden, dass die Magnetfeldregelung mit hoher Genauigkeit funktioniert. Es wird eine Genauigkeit von besser als 10^{-4} des maximalen Feldes von 1.5 T erreicht, also weniger als 150uT, der dreifachen Stärke des Erdmagnetfelds. Vor allem die Bestrahlungszeit mit Protonen und die Bestrahlung bei niedrigen Energien profitiert von der Magnetfeldregelung, da hier das Extraktionsniveau der Magnete relativ gering ist und das Durchlaufen der vordefinierten Hystereseschleife prozentual mehr Zeit im Zyklus in Anspruch nimmt. Durch den Wegfall dieser Phase wird daher pro Zyklus mehr Zeit eingespart. Die Messungen zeigen, dass im Beschleunigerzyklus trotz der fehlenden Wartezeiten, die bis zu 24% betragen, eine gleichbleibend gute Strahlqualität erreicht wird. Dies wurde mit Vergleichsmessungen gezeigt, bei denen der Strahl mit und ohne Feldregelung vermessen wurde. Untersucht wurde eine große Stichprobenmenge aus dem Parameterraum, gegeben durch zwei Ionensorten mit jeweils 255 Strahlenergien, 10 verschiedenen Teilchenraten und 4 Strahlbreiten. Außerdem wurde die Energie des Strahls nachgemessen.
Für die Einführung in den Therapiebetrieb musste eine Impactanalyse gemacht werden, die mögliche Auswirkungen des neuen Verfahrens behandelt. Das Risiko für Patienten, Mitarbeiter und Dritte darf durch die Magnetfeldregelung nicht erhöht werden. Daraus entstand auch die Forderung nach einem redundanten System, das Fehler erkennt und die Bestrahlung abbricht.
Die mittlere Leistungsaufnahme des Beschleunigers des Heidelberger Ionenstrahltherapiezentrums liegt bei etwa 1 MW, bei einem Jahresenergieverbrauch von 8 GWh mit Kosten von etwa 1 Million Euro. Dies entspricht einer deutschen Kleinstadt mit 10000 Einwohnern. Die Verkürzung der Zykluszeiten wirkt sich direkt auf die Bestrahlungszeit und auf die Energiekosten aus. Würde man die Anlage durch die Zeiteinsparungen kürzer betreiben, würde man etwa 2 GWh pro Jahr sparen, was die Stromkosten um etwa 250000 Euro reduziert.
Zusätzlich zu den eingesparten Kosten wird auch die Bestrahlungszeit kürzer und damit auch die Zeit, die der Patient bei der Behandlung fixiert wird. Die Behandlung für die Patienten wird angenehmer. Man kann aber auch durch die eingesparte Bestrahlungszeit pro Patient entsprechend mehr Patienten behandeln. Das heißt man kann an Stelle von 700 Patienten im Jahr 910 Patienten mit einem Tumor behandeln. Dieser für die Patienten willkommene Effekt bedeutet auf der anderen Seite für HIT aber auch Mehreinnahmen von 4.2 Millionen Euro im Jahr.
Das Konzept der Magnetfeldregelung kann auch an anderen Beschleunigeranlagen zum Einsatz kommen. Dazu müssen die Magnete mit den Sonden bestückt werden und die Magnetnetzgeräte einen Eingang für einen Zusatzsollwert bekommen. Das Beschleunigerkontrollsystem kann erweitert werden, damit es einen Sollwert mit allen notwendigen Kalibrierungen berechnen kann. Der HIT Integrator wird dann als eigenständiges Gerät in das Kontrollsystem eingebunden.
In der vorliegenden Arbeit wurden Messungen zur Plasmadynamik eines Lorentz-Drift- Beschleunigers (LDB) durchgeführt. Dieser basiert auf einer koaxialen Elektrodengeometrie. Bei einem Überschlag führt der entstehende Stromfluss zu einemMagnetfeld, sodass die gebildeten Ladungsträger durch die resultierende Lorentzkraft beschleunigt werden. Es hat sich gezeigt, dass die Abhängigkeit von Durchbruchspannung und Druck dem charakteristischen Verlauf einer Paschenkurve folgt.
Die Strom-Spannungs-Charakteristik des Versuchsaufbaus wurde in Konfigurationen mit und ohne Funkenstrecke untersucht. Mit Hilfe von diesem als Schalter fungierenden Spark-Gaps konnte bei Durchbruchspannungen gemessen werden, die oberhalb des Selbstdurchbruchs liegen.
Es zeigte sich, dass die im Versuchaufbau verwendete Funkenstrecke keinen wesentlichen Einfluss auf die Entladung hat. Es kommt an der Funkenstrecke lediglich zu einem Spannungsabfall im Bereich einiger hundert Volt, der den Verlauf derEntladung im LDB allerdings nicht beeinflusst.
Der Lorentz-Drift-Beschleuniger könnte in Zukunft zur Erzeugung eines Druckgradienten verwendet werden, indem Teilchen von einem Rezipienten in einen Zweiten beschleunigt werden. Als Voruntersuchung zur Eingnung dieses als Lorentz-Drift-Ventil bezeichneten Konzeptes wurden Messungen durchgeführt, die den Einfluss der Durchbruchspannung auf die Teilchenbeschleunigung mit Hilfe eines piezokeramischen Elementes untersuchen. So wurde der magnetische Druck bzw. die entsprechende Kraft einer Entladungswolke in Abhängigkeit von Durchbruchspannungen bis etwa 9,5 kV untersucht. Es hat sich gezeigt, dass der Einsatz von hohen Spannungen sinnvoll ist, da sich die auf das Piezoelement einwirkende Kraft quadratisch zur Durchbruchspannung verhält. So wurde die maximale Kraft von 0,44N bei einer Zündspannung von 9,52 kV gemessen.
Zudem wurde untersucht, in welchem Druckbereich der Einfluss der Druckwelle zu messen und wie sich die Geschwindigkeit der Ausbreitung der Druckwelle bei verschiedenen Durchbruchspannungen verhält. Bei einer Entfernung von 231mm zwischen Elektrodengeometrie und Piezoelement hat sich gezeigt, dass im Druckbereich unterhalb von etwa 0,2mbar kein wesentlicher Einfluss des Gasdruckes auf die Piezospannung erkennbar ist. Dies lässt sich durch die geringe Teilchenanzahl im Arbeitsgas begründen, sodass Teilchenstöße vernachlässigt werden können. Die maximale gemessene Geschwindigkeit der durch die Entladung verursachten Druckwelle liegt bei 55 km s ± 10%.
Die gemessene Plasmadynamik lässt darauf schließen, dass das Konzept eines gepulsten Lorentz-Drift-Ventils insbesondere mit hohen Durchbruchspannungen realisierbar ist. Zur Erzeugung eines dauerhaften Druckgradienten müsste die Repetitionsrate allerdings ausreichend hoch sein, sodass der rückfließende Gasdurchsatz geringer ist als die durch den LDB erzeugte Drift. Geht man von der Schallgeschwindigkeit als Rückflussgeschwindigkeit der Teilchen aus, so sind mindestens Repetitionszeiten im Bereich einer Millisekunde erforderlich.
Ergänzend zu den durchgeführten Untersuchungen ist es sinnvoll, die bisherigen Messungen durch Einbau eines Triggers zu verifizieren. Ein Trigger erzeugt eine Vorentladung mit deren Hilfe die eigentliche Entladung auch im Bereich unterhalb des Selbstdurchbruchs gezündet werden kann.
The Compressed Baryonic Matter (CBM) experiment [1] is a fixed target heavy-ion experiment that will operate at the international Facility for Antiproton and Ion Research (FAIR) [2] now under construction in Darmstadt, Germany. The experiment intends to study rare probes, which are emitted from heavy ion collisions with a beam energy of 4 to 45 AGeV. A focus is laid to the short lived open charm particles and to particles decaying into di-lepton pairs. Handling the up to 107 Au+Au collisions/s required for generating those probes with sufficient statistics, as much as reaching the required sensitivity for observing them, forms a major challenge for the silicon detectors of the experiment. We present the concept and the development status of two central detectors of CBM, the CMOS pixel based micro vertex detector (MVD) and the micro-strip detector based silicon tracking system (STS).
22nd International Workshop on Vertex Detectors, 15-20 September 2013 Lake Starnberg, Germany
In the presence of a minimal length, physical objects cannot collapse to an infinite density, singular, matter point. In this paper, we consider the possible final stage of the gravitational collapse of "thick" matter layers. The energy momentum tensor we choose to model these shell-like objects is a proper modification of the source for "noncommutative geometry inspired," regular black holes. By using higher momenta of Gaussian distribution to localize matter at finite distance from the origin, we obtain new solutions of the Einstein equation which smoothly interpolates between Minkowski's geometry near the center of the shell and Schwarzschild’s spacetime far away from the matter layer. The metric is curvature singularity free. Black hole type solutions exist only for "heavy" shells; that is, M >= Me, where Me is the mass of the extremal configuration. We determine the Hawking temperature and a modified area law taking into account the extended nature of the source.
Das Ziel dieser Masterarbeit ist die Auslegung des Kickers für den Bunch-Kompressor des FRANZ-Projektes. Anhand eines Modells wurden die verschiedenen Möglichkeiten der Einkopplung sowie das Feld zwischen den Kondensatorplatten bereits untersucht. In der vorliegenden Arbeit wird der Kicker mit Hilfe des Programms CST Microwave Studio erstellt und optimiert, sodass er nach Abschluss der Untersuchungen in die Fertigung gehen kann. Dabei ist der erste Schwerpunkt der Untersuchungen die Auslegung und Optimierung der Kondensatorplatten, die für die Auslenkung der Mikro-Bunche im FRANZ-Projekt verantwortlich sind. Zu Beginn der Masterarbeit gab es gezielte Winkelverteilungen, die der Kicker im Rahmen des FRANZ-Projektes erreichen sollte. Nachdem ein Erreichen dieser Werte nur bedingt möglich war, wurden verschiedene Abschnitte des FRANZ-Projektes neu überdacht und die Anforderungen an den Kicker änderten sich dadurch grundlegend. Aus diesem Grund wurde der Kicker zu Beginn der Arbeit für eine Frequenz von 5 MHz ausgelegt, wohingegen er im Rahmen der neuen Anforderungen für eine Resonanzfrequenz von 2,57 MHz ausgelegt wurde. Die Untersuchung der optimalen Resonanzfrequenz für die Anforderungen des Kickers stellt den zweiten Schwerpunkt dieser Arbeit dar.
Nach dem einführenden Theorieteil werden in den darauffolgenden Kapiteln zuerst die Auslegung und die Vermessung der drei Tripletts an der GSI in Darmstadt beschrieben und dann versucht mit Hilfe von LORASR einen Akzeptanzrahmen der MEBT-Sektion (Medium Energy Beam Transport) für ein Teilchenpaket anzugeben. Anschließend werden die Ergebnisse aus Feldvermessung und CST EM STUDIO Feldsimulationen verglichen. Damit soll die Frage, inwieweit es mit Particle Tracking Simulationen, in denen mit in CST EM STUDIO simulierten und anschließend in BENDER importierten Feldern gearbeitet wird, möglich ist, zutreffende Aussagen zu machen, beantwortet werden. Im letzten Kapitel werden wiederum die Ergebnisse dieser Simulationen präsentiert und ihre Bedeutung, im Vergleich mit den erweiterten Untersuchungen der Transporteigenschaften durch verschiedene aus überlagerten Multipolfeldern generierten Magnetfelder, eingeordnet. Abschließend wird nochmals ein Fazit zur Aussagekraft der Ergebnisse und der Folgen für den Strahltransport gezogen und ein Ausblick auf die noch ausstehenden Schritte und weitere experimentelle Analyseoptionen gegeben.
We report on the event-by-event multiplicity fluctuations of identified particles in central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. Employing a novel approach we unfolded the moments of the unknown multiplicity distributions of protons (p), kaons (K), pions (π) and electrons. Using these moments we reconstructed an excitation function of the fluctuation measure νdyn[A;B], with A and B denoting different particle types. Specifically, we reconstructed νdyn for the [p, π], [p, K] and [K, π] pairs. The energy dependence of νdyn is in agreement with previously published NA49 results on the related measure σdyn. Moreover, for [K; p] and [K;p] pairs, we discovered a dependence of the fluctuation measure νdyn on the phase space coverage (acceptance). Interestingly for the [p,π] case no significant acceptance dependence was observed. These observations provide a likely explanation of the reported differences between measurements of NA49 and those of STAR in central Au+Au collisions.
The study of energy and system size dependence of fluctuations of identified hadrons is one of the key goals of NA61/SHINE at the CERN SPS. Results may allow to discover the critical point (CP) of strongly interacting matter as well as to uncover properties of the onset of deconfinement (OD). Measured fluctuations are affected by numerous other effects like volume fluctuations and conservation laws. NA49 seems to observe fluctuations possibly related to the CP in collisions of medium size nuclei at the top SPS energy. However, this result will remain inconclusive until systematic data on energy and system size dependence will be available. Moreover, fluctuations in p+p as well as in Pb+Pb interactions should be better understood. In this contribution new results on multiplicity fluctuations of identified hadrons in p+p interactions at the CERN SPS energies will be presented. The NA61 data will be compared with the corresponding results on central Pb+Pb collisions of NA49 in the common acceptance region of both experiments. Furthermore, predictions of models (EPOS, UrQMD and HSD) for p+p interactions will be tested.
While the existence of a strongly interacting state of matter, known as “quark-gluon plasma” (QGP), has been established in heavy ion collision experiments in the past decade, the task remains to map out the transition from the hadronic matter to the QGP. This is done by measuring the dependence of key observables (such as particle suppression and elliptic flow) on the collision energy of the heavy ions. This procedure, known as "beam energy scan", has been most recently performed at the Relativistic Heavy Ion Collider (RHIC).
Utilizing a Boltzmann+hydrodynamics hybrid model, we study the collision energy dependence of initial state eccentricities and the final state elliptic and triangular flow. This approach is well suited to investigate the relative importance of hydrodynamics and hadron transport at different collision energies.
We derive the Polyakov-loop thermodynamic potential in the perturbative approach to pure SU(3) Yang-Mills theory. The potential expressed in terms of the Polyakov loop in the fundamental representation corresponds to that of the strong-coupling expansion, of which the relevant coefficients of the gluon energy distribution are specified by characters of the SU(3) group. At high temperature, the potential exhibits the correct asymptotic behavior, whereas at low temperature, it disfavors gluons as appropriate dynamical degrees of freedom. To quantify the Yang-Mills thermodynamics in confined phase, we introduce a hybrid approach which matches the effective gluon potential to that of glueballs, constrained by the QCD trace anomaly in terms of dilaton fields.
We study the impact of nonequilibrium effects on the relevant signals within a chiral fluid dynamics model including explicit propagation of the Polyakov loop. An expanding heat bath of quarks is coupled to the Langevin dynamics of the order parameter fields. The model is able to describe relaxational processes, including critical slowing down and the enhancement of soft modes near the critical point. At the first-order phase transition we observe domain formation and phase coexistence in the sigma and Polyakov loop field leading to a significant amount of clumping in the energy density. This effect gets even more pronounced if we go to systems at finite baryon density. Here the formation of high-density clusters could provide an important observable signal for upcoming experiments at FAIR and NICA.We conclude that improving our understanding of dynamical symmetry breaking is important to give realistic estimates for experimental observables connected to the QCD phase transition.
The QGP that might be created in ultrarelativistic heavy-ion collisions is expected to radiate thermal dilepton radiation. However, this thermal dilepton radiation interferes with dileptons originating from hadron decays. In the invariant mass region between the f and J=y peak (1GeV <= M l+l <=. 3GeV) the most substantial background of hadron decays originates from correlated DD¯ -meson decays. We evaluate this background using a Langevin simulation for charm quarks. As background medium we utilize the well-tested UrQMD-hybrid model. The required drag and diffusion coefficients are taken from a resonance approach. The decoupling of the charm quarks from the hot medium is performed at a temperature of 130MeV and as hadronization mechanism a coalescence approach is chosen. This model for charm quark interactions with the medium has already been successfully applied to the study of the medium modification and the elliptic flow at FAIR, RHIC and LHC energies. In this proceeding we present our results for the dilepton radiation from correlated D¯D decays at RHIC energy in comparison to PHENIX measurements in the invariant mass range between 1 and 3 GeV using different interaction scenarios. These results can be utilized to estimate the thermal QGP radiation.
As microscopic transport models usually have difficulties to deal with in-medium effects in heavy-ion collisions, we present an alternative approach that uses coarse-grained output from transport calculations with the UrQMD model to determine thermal dilepton emission rates. A four-dimensional space-time grid is set up to extract local baryon and energy densities, respectively temperature and baryon chemical potential. The lepton pair emission is then calculated for each cell of the grid using thermal equilibrium rates. In the current investigation we inlcude the medium-modified r spectral function by Eletsky et al., as well as contributions from the QGP and four-pion interactions for high collision energies. First dielectron invariant mass spectra for Au+Au collisions at 1.25 AGeV and for dimuons from In+In at 158 AGeV are shown. At 1.25 AGeV a clear enhancement of the total dilepton yield as compared to a pure transport result is observed. In the latter case, we compare our outcome with the NA60 dimuon excess data. Here a good agreement is achieved, but the yield in the low-mass tail is underestimated. In general the results show that the coarse-graining approach gives reasonable results and can cover a broad collision-energy range.
This work presents an effective model for strongly interacting matter and the QCD equation of state (EoS). The model includes both hadron and quark degrees of freedom and takes into account the transition of chiral symmetry restoration as well as the deconfinement phase transition. At low temperatures T and baryonic densities ρB a hadron resonance gas is described using a SU(3)-flavor sigma-omega model and a quark phase is introduced in analogy to PNJL models for higher T and ρB. In this way, the correct asymptotic degrees of freedom are used in a wide range of T and ρB. Here, results of this model concerning the chiral and deconfinement phase transitions and thermodynamic model properties are presented. Large hadron resonance multiplicities in the transition region emphasize the importance of heavy-mass resonance states in this region and their impact on the chiral transition behavior. The resulting phase diagram of QCD matter at small chemical potentials is in line with latest lattice QCD and thermal model results.
Spinodal crumbling
(2013)
Extending a previously developed two-phase equation of state, we simulate head-on relativistic lead-lead collisions with fluid dynamics, augmented with a finite-range term, and study the effects of the phase structure on the evolution of the baryon density. For collision energies that bring the bulk of the system into the mechanically unstable spinodal region of the phase diagram, the density irregularities are being amplified significantly. We also present results for the associated clump size distribution.
We analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS and LHC energies. Employing the UrQMD hybrid transport model we study the effects of the final hadron/resonance expansion phase on the hadron multiplicities established at hadronization. The bulk meson yields freeze out directly at hadronization whereas the baryon-antibaryon sector is subject to significant alterations, due to annihilation and regeneration processes. We quantify the latter changes by survival factors for each species which are applied to modify the statistical model predictions for the data. The modified SM analysis recovers the hadronization points, which coincide with the recent lattice QCD predictions of the parton-hadron transition line at finite baryochemical potential.