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Rapidity and transverse momentum dependence of inclusive J/ψ production in pp collisions at √s=7 TeV
(2011)
The ALICE experiment at the LHC has studied inclusive J/ψ production at central and forward rapidities in pp collisions at √s=7 TeV. In this Letter, we report on the first results obtained detecting the J/ψ through the dilepton decay into e+e− and μ+μ− pairs in the rapidity ranges |y|<0.9 and 2.5<y<4, respectively, and with acceptance down to zero pT. In the dielectron channel the analysis was carried out on a data sample corresponding to an integrated luminosity Lint=5.6 nb−1 and the number of signal events is NJ/ψ=352±32(stat.)±28(syst.); the corresponding figures in the dimuon channel are Lint=15.6 nb−1 and NJ/ψ=1924±77(stat.)±144(syst.). The measured production cross sections are σJ/ψ(|y|<0.9)=10.7±1.0(stat.)±1.6(syst.)−2.3+1.6(syst.pol.)μb and σJ/ψ(2.5<y<4)=6.31±0.25(stat.)±0.76(syst.)−1.96+0.95(syst.pol.)μb. The differential cross sections, in transverse momentum and rapidity, of the J/ψ were also measured.
Fragment mass distributions for fission after full momentum transfer were measured in the reactions of 30Si,34,36 S,31P,40Ar + 238U at bombarding energies around the Coulomb barrier. Mass distributions change significantly as a function of incident beam energy. The asymmetric fission probability increases at sub-barrier energy. The phenomenon is interpreted as an enhanced quasifission probability owing to orientation effects on fusion and/or quasifission. The evaporation residue (ER) cross sections were measured in the reactions of 30Si + 238U and 34S + 238U to obtain information on fusion. In the latter reaction, significant suppression of fusion was implied. This suggests that fission events different from compound nucleus are included in the masssymmetric fragments. The results are supported by a model calculation based on a dynamical calculation using Langevin equation, in which the mass distribution for fusion-fission and quasifission fragments are separately determined.
We give a brief overview of recent work examining the presence of α-clusters in light nuclei within the Skyrme-force Hartree-Fock model. Of special signif cance are investigations into α-chain structures in carbon isotopes and 16O. Their stability and possible role in fusion reactions are examined in static and time-dependent Hartree-Fock calculations. We f nd a new type of shape transition in collisions and a centrifugal stabilization of the 4α chain state in a limited range of angular momenta. No stabilization is found for the 3α chain.
The present limits of the upper part of the nuclear map are rather close to the beta stability line while the unexplored area of heavy neutron rich nuclides (also those located along the neutron closed shell N = 126 to the right hand side of the stability line) is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis. For elements with Z > 100 only neutron deficient isotopes (located to the left of the stability line) have been synthesized so far. The “north-east” area of the nuclear map can be reached neither in fusion–fission reactions nor in fragmentation processes widely used nowadays for the production of new nuclei. Multi-nucleon transfer processes in near barrier collisions of heavy ions seem to be the only reaction mechanism allowing us to produce and explore neutron rich heavy nuclei including those located at the superheavy island of stability. Neutron capture process can be also considered as an alternative method for the production of long-lived neutron rich superheavy nuclei. Strong neutron fluxes might be provided by nuclear reactors and nuclear explosions in laboratory frame and by supernova explosions in nature.
We found that a true ternary fission with formation of a heavy third fragment (a new kind of radioactivity) is quite possible for superheavy nuclei due to the strong shell effects leading to a three-body clusterization with the two doubly magic tin-like cores. The three-body quasifission process could be even more pronounced for giant nuclear systems formed in collisions of heavy actinide nuclei. In this case a three-body clusterization might be proved experimentally by detection of two coincident lead-like fragments in low-energy U+U collisions.
The crossbar H-mode (CH) cavity is an accelerating structure operated in the H21(0) mode. The robustness of the crossbar geometry allows one to realize room temperature as well as superconducting linac cavities. The shunt impedance characteristics of this structure are attractive to develop proton and heavy ion linacs in the low and medium beta range. A first room temperature eight-cell prototype has proven the feasibility of the crossbar design in terms of mechanical construction, copper plating, and cooling. An innovative rf coupling concept has been developed where two CH cavities are connected by a two gap E010-mode resonator which, at the same time, provides transverse focusing by a quadrupole triplet. The concept has been applied in the design of the new FAIR proton linac and a scaled model of the second cavity of this injector has been built and tested too. The full scale prototype is now under construction at the University of Frankfurt. In this paper, the room temperature CH cavity development as well as the general layout of the FAIR proton injector (70 MeV, 325 MHz, 70 mA) is presented and discussed.
Mit der hier vorliegenden Arbeit ist das Entladungsverhalten einer Dielektrischen Barriere Entladung anhand der elektrischen Parameter untersucht worden. Dazu wurde ein planparallele Elektrodenkonfiguration entwickelt und aufgebaut, die mit einer Sinus-Spannungs von maximal 5000 Vss und einer Frequenz von 5 kHz-20 kHz angesteuert wurde. Als Arbeitsgas wurde Argon im Druckbereich von 100 mbar - 1000 mbar verwendet. Auf diese Weise konnte ein Plasma erzeugt werden, in das bei einer maximalen Transfereffiienz von 96%, eine mittlere Leistung von bis zu 845 mW eingekoppelt werden konnte.
Da die Dielektrische Barriere Entladung auf Grund der Abschirmung der Elektroden vom Gasraum einige Besonderheiten gegenüber eines klassischen kapazitiv eingekoppelten Plasmas aufweist, können keine Rückschlüsse mittels einer einfachen Strom-Spannungsmessung auf die Vorgänge im Plasma gemacht werden.
Um trotzdem Einblick in die Entladung zu erhalten, wurde das von [Tra08] vorgeschlagene Ladungstransportmodel für die Analyse herangezogen und an den hier vorliegenden experimentellen Aufbau angepasst. So konnte unter anderem der Ein
uss der auf den Dielektrika befindlichen Restladungsträger auf die Ausbildung der Entladung untersucht werden. Des Weiteren ist aus den gewonnen Größen die Elektronendichte des Plasmas bestimmt worden. Diese liegt bei der hier untersuchten dielektrischen Glimmentladung, je nach Gasdruck und Frequenz, im Bereich zwischen 5 X 10exp9 - 2 X 10exp10 1/cm3 . Auch konnten in diesem Zusammenhang qualitative Aussagen über die Entwicklung der Elektronentemperatur gemacht werden.
Zusammen mit Kurzzeitaufnahmen, die den Verlauf der Entladung dokumentieren und den in [Sch11] gemachten Untersuchungen zur Excimerstrahlung konnte so ein umfassendes Bild der Vorgänge im Plasma erstellt und Kriterien erarbeitet werden, die den für eine Dielektrische Barriere Entladung typischen Ubergang zwischen einer Glimmentladung zu einer filamentierten Entladung erklären können.
Im Rahmen dieser Diplomarbeit haben Arbeiten am Elektronen-Streuexperiment von Prof. J. Jacoby und Dr. R. Berezov an der Goethe-Universität Frankfurt stattgefunden. Am Experiment wurden durch Møller-Streuung verschränkte Elektronen auf ihre Spin-Abhängigkeit untersucht. Die Untersuchung erfolgte als Koinzidenzmessung, dessen Genauigkeit von der zeitlichen Auflösung der Detektoren abhängt. Als Koinzidenzlogik diente ein von Julian Schunk entwickeltes Datenerfassungsprogramm, das auf einem Oszilloskop installiert wurde...
Optische Untersuchungen des Entladungsverhaltens einer dielektrischen Barriere Entladung in Argon
(2011)
Im Rahmen dieser Arbeit wurde eine "Dielektrische Barriere Entladung" (DBE) mit planparalleler Elektrodengeometrie aufgebaut und mittels optischer Diagnostik untersucht und analysiert. Die mit der Dielektrischen Barriere Entladung erzeugte Strahlung soll für die Wassersterilisation durch UV-Entkeimung genutzt werden.
Als Arbeitsgas wurde Argon verwendet. Argon Excimere emittieren VUV-Strahlung mit einer Wellenlänge von 126nm. Die Ansteuerung der DBE erfolgte mit einer Sinusspannung. Die Amplitude der Sinusspannung wurde von 1600V/SS-5000V/SS bei einer Frequenz von 5kHz-20kHz und einem Druck von 100mbar-1000mbar variiert.
Bei der Entwicklung einer Lampe zur Wassersterilisation ist die Kenntnis der Effizienz notwendig. In dieser Arbeit wurde daher untersucht, welchen Einfluss Druck, Spannung und Frequenz auf die VUV-Konversionseffizienz (Verhältnis der eingekoppelten Leistung zur Lichtleistung bei 126nm) haben. Bei einem Druck von 600mbar und einer Effektivspannung von ca. 1050V konnte bei 6kHz eine
maximale VUV-Konversionseffizienz von ca. 6% erzielt werden. Die Lichtleistung bei einer Wellenl¨ange von 126nm betrug dabei 11, 5mW.
Die Bildung von Excimeren setzt das Vorhandensein von Argonatomen im metastabilen Zustand voraus. Zum einen entstehen diese metastabilen Anregungszustände durch direkte Anregung bei Stoßprozessen, zum anderen können sie durch Abregung eines höheren Anregungszustandes unter Aussendung von Strahlung entstehen. Die Wellenlängen, der bei einem solchen Übergang emittierten Strahlung (Erzeugerlinien) befinden sich im sichtbaren Bereich. Zur Analyse des sichtbaren Spektrums wurde ein Spektrometer verwendet. Es konnte ein direkter Zusammenhang zwischen den Erzeugerlinien und der Entstehung von Excimerstrahlung nachgewiesen werden. Eine Messung dieser Erzeugerlinien kann daher als erster Indikator für die Erzeugung von VUV-Excimerstrahlung dienen. Bei dielektrischen Barriere Entladungen muss zwischen drei Entladungsformen unterschieden werden. Man unterscheidet homogene, filamentierte und quasihomogene Entladungen. Zur genaueren Untersuchung der Dynamik der DBE und der Entstehung dieser unterschiedlichen Entladungsformen wurden Aufnahmen mittels Kurzzeitkamera angefertigt und in Bezug auf die Parameter Druck, Spannung und Frequenz untersucht. In Zusammenarbeit mit [Hoc11] wurden Entladungsphasendiagramme erstellt, welche unter Kenntnis von Druck, Spannung und Frequenz eine Zuordnung der Entladungsform bei den jeweiligen Parametern ermöglichen. Es wurde gezeigt, dass die maximale VUV-Konversionseffizienz im Bereich homogener Entladungen erreicht wird und das homogene Entladungen bei Variation der Parameter nur einen kleinen Bereich im Vergleich zu den anderen Entladungsformen einnehmen.
Optimierung der Rekonstruktionsparameter zur Messung von Quarkonia im zentralen ALICE Detektor
(2011)
Seit den ersten Kollisionen im November 2009 läuft der LHC am CERN und dringt in noch nie dagewesene Energiebereiche vor. Die Schwerionenkollisionen innerhalb des ALICE Detektors sollen Aufschluss über die stark wechselwirkende Materie und ihre verschiedenen Phasen geben. Dem liegt die Untersuchung des Quark-Gluon-Plasmas zugrunde. Eine Signatur des Quark-Gluon-Plasmas ist die Rate von produzierten Quarkonia. Diese zerfallen in Leptonenpaare und sind damit zu identifizieren.
In der vorliegenden Arbeit wird diese Rate zur Messung von Quarkonia aufgegriffen und untersucht. Bei der Untersuchung der Simulation durch die Selektion der e++e--Paare, die ausschließlich aus einem J/y stammen, lässt sich ein Massenspektrum produzieren, das im Rahmen dieser Arbeit genauer betrachtet wurde. Durch die genaue Untersuchung der Bremsstrahlung und deren Lokalisierung lässt sich zeigen, dass besonders der ITS ein hohes Maß an Bremsstrahlungsprozessen mit sich bringt, was auf die große Materialanhäufung zurückzuführen ist. Um dies näher zu untersuchen, wurde das Augenmerk auf den ITS gelegt. Eines der wichtigsten Merkmale, die den Bremsstrahlungsprozess beschreiben, ist der Energieverlust. Durch die Bethe-Heitler-Funktion lässt sich der gesamte Detektor nur bedingt beschreiben. Erst die Betrachtung, die sich mit einer Einschränkung auf den ITS und den Azimutwinkel beschäftigt, zeigt eine genaue Beschreibung durch die Parameter der Funktion.
Nach der genauen Beschreibung der Bremsstrahlung wurden verschiedene Methoden entwickelt, in denen die Bremsstrahlungsprozesse innerhalb des invarianten Massenspektums der e++e--Paare ausgeschnitten werden können. Die Methoden der Selektion durch die Anzahl der Spurpunkte sowie die Selektion durch die Position der Spurpunkte zeigen, dass bereits minimale Selektionen ein sehr gutes Signal ergeben. Durch den Vergleich mit den herkömmlichen Selektionen SPDany und SPDfirst, zeigt sich, dass hierbei viel Signal verloren geht und diese Methode für bestimmte Analysen optimiert werden kann.
Durch die Anwendung auf die Datensätze, die während einer Strahlzeit im Jahr 2010 genommen wurden, bestätigte sich die Vermutung. Durch die Selektion von SPDany wird das Signal reduziert. Vergleicht man die Anzahl der Einträge im Signalbereich durch die Reduktion der Teilchen ohne Spurpunkte im ITS (NITSpunkten>0) zu der Anzahl der Einträge durch SPDany, ergibt dies eine Verminderung von bis zu 40%. Die Ursache für den großen Verlust innerhalb des Signalbereichs wird zusätzlich verstärkt, indem der SPD durch Kühlungsprobleme ausgeschaltet ist.
Eine weitere Methode, die untersucht wurde, war die Reduktion der Auswirkungen von Bremsstrahlung mit Hilfe der Kinkanalyse. Diese Methode ließ keine qualitativen Rückschlüsse auf die Analyse der Bremsstrahlung zu.
Dennoch zeigt das Ergebnis, dass das Signal von J/y’s in Proton-Proton Kollisionen um mehr als 40% mehr Einträge verbessert werden kann und sich dieses Prinzip nicht nur theoretisch in den simulierten Daten niederschlägt sondern auch in den untersuchten Datensätzen. Nun gilt es, diese Methode auch in anderen Studien einzubauen, um so eine alltagstaugliche Überprüfung der Erkenntnisse zu gewährleisten.
Das Compressed Baryonic Matter Experiment (CBM) wird im Rahmen der Facility for Antiproton and Ion Research (FAIR) entwickelt, um das Phasendiagramm stark wechselwirkender Materie vorwiegend im Bereich hoher Dichte ausgiebig zu studieren. Dazu sollen Kollisionen schwerer Ionen durchgeführt werden und die Reaktionsprodukte mit hoher Präzision in Teilchendetektoren gemessen und identfiziert werden. Eine wichtige Aufgabe besteht in der Unterscheidung von Elektronen und Pionen, zu der ein Übergangsstrahlungszähler (Transition Radiation Detector) beiträgt. Übergangsstrahlung wird im relevanten Impulsbereich dieser Teilchen nur von Elektronen emittiert und soll im Detektor registriert werden.
In der vorliegenden Arbeit wird die Entwicklung dieses Detektors auf Basis von Vieldrahtproportionalkammern (Multiwire Proportional Chamber ) hauptsächlich anhand von Simulationen diskutiert, aber auch erste Testmessungen eines Prototypen vorgestellt. Der Schwerpunkt der Simulationen eines einzelnen Detektors liegt in der Untersuchung der Effiienz in Abhängigkeit seiner Dicke.
Der Übergangsstrahlungszähler für CBM wird aus mehreren Detektorlagen bestehen. Daher wird außerdem die Effizienz des Gesamtsystems analysiert, indem verschiedene Methoden zur Kombination der einzelnen Signale angewendet werden. Darüber hinaus wird die Effizienz des verfolgten Detektorkonzepts in Abhängigkeit des Radiators, der Anzahl der Detektorlagen, sowie des Teilchenimpulses präsentiert.
Die vorliegende Arbeit beschäftigt sich mit optischen und elektrischen Untersuchungen an einer koaxial aufgebauten Lorentz-Drift-Geometrie. So wurden Messungen an der Lorentz-Drift-Sputterquelle bezüglich der Durchbruchspannung durchgeführt. Es hat sich gezeigt, dass das Verhalten der Durchbruchspannung in Abhängigkeit vom Druck trotz der koaxialen Elektrodengeometrie vergleichbar mit der Paschenkurve fur eine planparallele Anordnung ist.
Zur Untersuchung des Sputterverhaltens wurden zunächst einige Kurzzeitaufnahmen mit einer Belichtungszeit im Mikrosekundenbereich durchgefuhrt, um so die Ausbreitung der Plasmawolke zu betrachten. Bei einem Durchbruch führt der Stromfluss zu einem Magnetfeld, sodass ein Lorentz-Drift entsteht. Durch die resultierende Kraft wird das Plasma beschleunigt.
Es zeigt sich, dass sich die Plasmawolke mit zunehmender Zeit bzw. zunehmendem Abstand von den Elektroden homogener im Rezipient verteilt. Da durch die Ausbreitung der Plasmafront auch ausgelöstes Elektrodenmaterial zu einem entsprechend platzierten Substrat beschleunigt wird, lagert sich dort eine dünne Schicht an.
Die Ablagerungen am Substrat wurden bei verschiedenen Drucken und verschiedenen Abständen zu den Elektroden betrachtet. Erste Messungen zeigen, dass die Schichten mit größerem Abstand homogener werden und besser am Substrat haften bleiben, jedoch die Schichtdicke geringer wird. Bei geringem Abstand lagern sich vergleichsweise dicke Schichten an, die jedoch sehr inhomogen und instabil sind. Durch Optimierung sollte es aber möglich sein, einen gewünschten Kompromiss aus Schichtdicke, Stabilität und Homogenität zu finden.
Bei niedrigeren Drucken und somit hohen Durchbruchspannungen kommt es aufgrund der höheren Stromdichte zu stärkeren Lorentz-Drifts, sodass die Teilchenenergien im Plasma steigen und es zu dickeren Ablagerungen kommt.
Die Schlussfolgerung dieser Arbeit ist, dass die Beschichtung durch eine Lorentz-Drift-Geometrie prinzipiell möglich ist. Es konnten bisher qualitative Messungen durchgeführt werden, die jedoch noch quantitativ verifiziert werden sollten.
Design and optimization of the lattice of the superconducting synchrotron SIS300 for slow extraction
(2011)
The superconducting synchrotron SIS300 is planned to be built at the new Facility for Antiproton and Ion Research (FAIR), at GSI-Darmstadt [1]. SIS300 will be a versatile machine, which by means of a low-energy stretcher-mode or a high-energy ramped-mode will provide slowly extracted heavy ion beams towards the experimental areas. To reach the required maximum field of 4.5 T, cos(θ) magnets are necessary. Thus, SIS300 will become the first superconducting synchrotron worldwide with cos(θ) magnets providing resonant slow extraction.
Since SIS300 will be installed in the same tunnel as the SIS100 synchrotron, the dipole layout of SIS300 cannot be freely chosen. Thus, a standard lattice cannot be applied. A redesign of the SIS300 lattice accepting compromises concerning the positions and phase advances between the optical elements has been proposed. Using the analytical model of the slow extraction, firstly proposed by Kobayashi, and the analytical description of the resonance driving modes, a multiobjective optimization algorithm has been developed for the optimization of the lattice under the given boundary conditions. The final goal of the lattice optimization is a higher efficiency of the slow extraction. The results are evaluated by means of tracking simulations performed with the code Elegant.
The field quality in superconducting cos(θ) magnets is determined by the positions of the superconducting cable and the static and time-dependent effects of the current in the cable. Furthermore, the fast ramp rates of 1 T/s in the dipoles, which are fifty times faster than in any other superconducting cos(θ) magnet, together with the fact that the aperture is smaller than in conventional accelerator magnets, makes it extremely difficult to obtain a high-quality magnetic field. The unavoidable field errors affect the beam dynamics and worsen the slow extraction efficiency. Therefore, the field errors in the SIS300 dipoles have been estimated, and their effects have been taken into account in the optimization algorithm. As a result a compensation scheme has been proposed, in which time-dependent gradients in the sextupoles counteract the decay of the sextupole field errors in the dipole magnets during the slow extraction. For the limits where the compensation was no longer possible, tolerances to the magnet field errors have been determined.
Im Rahmen der Bachelorarbeit wurden verschiedene Messungen am CH-Modell des Protonen - Linearbeschleunigers für FAIR durchgeführt.
Zu Beginn wurde die Wirkung der Tuner auf das elektrische Feld im Resonator und die Frequenz untersucht. Aus den systematischen Messungen konnte man feststellen, wie die Tuner das elektrische Feld beeinflussen. Außerdem konnte man sehen, dass die Tuner zu einer Erhöhung der Frequenz führen, was auch durch den theoretischen Hintergrund erwartet wurde. Aus den so gewonnenen Erkenntnissen konnte nun versucht werden, die Spaltspannungen an eine Vorgabe aus LORASR anzupassen. Dies nahm den Hauptteil der Bachelorarbeit ein. Die Anpassung konnte durch Variation der Tuner und der Spaltlängen erreicht werden. Die Abweichungen zur LORASR - Vorgabe lagen alle, bis auf einen Wert, im vorgegebenen Bereich. Allerdings waren die Messungen nicht perfekt reproduzierbar, da es bei der Störkörpermessung zu Fehlern kam. Der Motor, der den Störkörper durch die CH-Struktur ziehen sollte, war in diesem Zeitraum defekt, wodurch sich die gemessenen Spaltspannungen etwas veränderten.
Weiterhin wurde noch eine Sensibilitätsuntersuchung bei Erwärmung des Niederenergieteils des Resonators und eine Modenuntersuchung durchgeführt.
Durch die Erwärmung des Niederenergieteils konnte man sehen, dass das Feld im Inneren des Resonators auf Temperaturunterschiede reagiert. Dies hat aber keinen Einfluss auf die Betriebsfähigkeit des Resonators, da die zu erwartenden Einflüsse auf den Resonator im Betrieb sehr gering sind. Die Modenuntersuchung hat die vorherigen Annahmen bestätigt. Die Hochfrequenzleistung wird über die Linse hinweg störungsfrei weitergegeben und die ersten 4 Moden schwingen alle in dem Modell an und sind messbar, wenn man außen in den Tanks einkoppelt.
The HITRAP linear decelerator currently being set up at GSI will provide slow, few keV/u highly charged ions for atomic physics experiments. The expected beam intensity is up to 105 ions per shot. To optimize phase and amplitude of the RF systems intensity, bunch length and kinetic energy of the particles need to be monitored. The bunch length that we need to fit is about 2 ns, which is typically measured by capacitive pickups. However, they do not work for the low beam intensities that we face. We investigated the bunch length with a fast CVD diamond detector working in single particle counting mode. Averaging over 8 shots yields a clear, regular picture of the bunched beam. Energy measurements by capacitive pickups are limited by the presence of intense primary and partially decelerated beam and hence make tuning of the IH-structure impossible. The energy of the decelerated fraction of the beam behind the first deceleration cavity was determined to about 10 % accuracy with a permanent dipole magnet combined with a MCP. Better detector calibration should help reaching the required 1%. Design of the detectors as well as the results of the measurements will be presented.
A test stand for optical beam tomography was developed. As a new non-destructive beam-diagnostic system for high current ion beams, the test stand will be installed in the low energy beam transport section (LEBT) of the Frankfurt Neutron Source (FRANZ) behind the chopper system. The test stand consists of a rotatable vacuum chamber with a mounted CCD camera. The maximum rotation angle amounts to 270°. In a first phase the optical beam profile measurement and 3D density reconstruction is tested with a time independent 10 keV He beam. The measurements and performance of data processing algorithms are compared with the beam transport simulations. In a later phase the performance with time dependent beams (120 keV, 200 mA) at a repetition rate of 250 kHz and a duty cycle of 2.5% has to be evaluated. An overview of the first phase results is shown.
Space charge lenses use a confined electron cloud for the focusing of ion beams. The focusing strength is given by the electron density whereas the density distribution influences the mapping quality of the space charge lens and is related to the confinement. The plasma parameters, loss as well as production mechanisms have a strong impact on plasma beam interactions. A scaled up space charge lens was constructed to investigate the properties of a nonneutral plasmas in detail. New non-interceptive diagnostic has been developed to characterize the collective behaviour of the confined nonneutral plasma in terms of an optimized lens design and parameters. Experimental results will be presented in comparison with numerical simulations.
A non-interceptive optical diagnostic system on the basis of beam tomography, was developed for the planned Frankfurt Neutron Source (FRANZ). The proton driver linac of FRANZ will provide energies up to 2.0 MeV. The measurement device will non-interceptively derive required beam parameters at the end of the LEBT at beam energies of 120 keV and a current of 200 mA. On a narrow space of 351.2 mm length a rotatable tomography tank will perform a multi-turn tomography with a high and stable vacuum pressure. The tank allows to plug different measurement equipment additionally to the CCD Camera installed, to perform optical beam tomography. A collection of developed algorithms provides information about the density distribution, shape, size, location and emittance on the basis of CCD images. Simulated, as well as measured data have been applied to the evaluation algorithms to test the reliability of the beam. The actual contribution gives an overview on the current diagnostic possibilities of this diagnostic system.
Intense ion beams with small phase space occupation (high brilliance) are mandatory to keep beam losses low in high current injector accelerators like those planned for FAIR. The low energy beam transport from the ion source towards the linac has to keep the emittance growth low and has to support the optimization of the ion source tune. The Frankfurt Neutron Source Facility FRANZ is currently under construction. An intense beam of protons (2 MeV, 200 mA) will be used for neutron production using the Li7(p,n)Be7 reaction for studies of the astrophysical s-process. A collimation channel, which can be adjusted to allow the transport of beams with a certain beam emittance, is an ideal tool to optimize the ion source tune in terms of beam brightness. Therefore a collimation channel in the Low Energy Beam Transport section will be used. Through defined apertures and transversal phase space rotation using focusing solenoids the beam halo as well as unwanted H2+ and H3+ fractions will be cut. Theoretical studies which were carried out so far and a first design of the setup will be presented.
Beam test of the direct plasma injection scheme (DPIS) is carried out successfully for the first time in China, by setting up a comprehensive test and research platform of RFQ and laser ion source. The C6+ beam is accelerated successfully, and the peak beam current reaches more than 6mA which is measured by a Faraday cup of unique structure. The RF power coupled into the RFQ cavity is also examined, and results reveal that it is the RF power of about 195kW that can produce the peak beam current.
A CW RFQ prototype
(2011)
A short RFQ prototype was built for RF-tests of high power RFQ structures. We will study thermal effects and determine critical points of the design. HF-simulations with CST Microwave Studio and measurements were done. The cw-tests with 20 kW/m RF-power and simulations of thermal effects with ALGOR were finished successfully. The optimization of some details of the HF design is on focus now. First results and the status of the project will be presented.
Beam measurements with the new RFQ beam matching section at the Frankfurt Funneling Experiment
(2011)
Funneling is a method to increase low energy beam currents in multiple stages. The Frankfurt Funneling Experiment is a model of such a stage. The experiment is built up of two ion sources with electrostatic lens systems, a Two-Beam-RFQ accelerator, a funneling deflector and a beam diagnostic system. The two beams are bunched and accelerated in a Two-Beam RFQ. A funneling deflector combines the bunches to a common beam axis. A new beam transport system between RFQ accelerator and deflector has been constructed and mounted. With these extended RFQ-electrodes the drift between the Two-Beam-RFQ and the rf-deflector will be minimized and therefore unwanted emittance growth reduced. After first rf measurements current work are beam tests with the improved Two-Beam-RFQ. First results will be presented.
Usually 4-ROD Radio Frequency Quadrupoles (RFQ) are built for frequencies up to 216 MHz. For higher frequencies 4-VANE structures are more common. The advantages of 4-Rod structures, the greater flexibility for tuning and being more comfortable for maintenance, are motivating the development of a 4-Rod RFQ for higher frequencies than 216 MHz. In particular a 325 MHz RFQ with an output energy of 3 MeV is needed for the proton linac for the FAIR project of GSI. This paper reports about the design studies and the latest developments of this RFQ.
For the injector upgrade at FNAL a 4-rod Radio Frequency Quadrupole (RFQ) with a resonance frequency of 200 MHz has been build. With this short structure of only 1.3 m a very compact injector design has been realized. Simulations with CST Microwave Studio® were performed for the design. Their results leading to the RF characterizations of the RFQ and the final RF setup which has been accomplished at IAP of the Goethe-University Frankfurt are presented in this paper.
The LANSCE linear accelerator at Los Alamos National Laboratory provides H− and H+ beams to several user facilities that support Isotope Production, NNSA Stockpile Stewardship, and Basic Energy Science programs. These beams are initially accelerated to 750 keV using Cockcroft-Walton (CW) based injectors that have been in operation for over 37 years. They have failure modes which can result in prolonged operational downtime due to the unavailability of replacement parts. To reduce long-term operational risks and to realize future beam performance goals in support of the Materials Test Station (MTS) and the Matter-Radiation Interactions in Extremes (MaRIE) Facility, plans are underway to develop a Radio-Frequency Quadrupole (RFQ) based front end as a modern injector replacement for the existing CW injectors. Our progress to date will be discussed.
n order to reach the desired intensities of heavy ion beams for the experiments at FAIR, SIS18 and SIS100 have to be operated with intermediate charge states. Operation with intermediate charge state heavy ions at the intensity level of about 1011 ions per cycle has never been demonstrated elsewhere and requires a dedicated upgrade program for SIS18 and a dedicated machine design for SIS100. The specific problems coming along with the intermediate charge state operation in terms of charge exchange processes at collisions with residual gas atoms, pressure bumps by ion induced desorption and corresponding beam loss appears far below the typical space charge limits. Thus, new design concepts and new technical equipment addressing these issues are developed and realized with highest priority. The upgrade program of SIS18 addressing the goal of minimum ionization beam loss and stable residual gas pressure conditions has been defined in 2005. A major part of this upgrade program has been successfully realized, with the result of a world record in accelerated number of intermediate charge state heavy ions.
Accelerator Driven Systems (ADS) are promising tools for the efficient transmutation of nuclear waste products in dedicated industrial installations, called transmuters. The Myrrha project at Mol, Belgium, placed itself on the path towards these applications with a multipurpose and versatile system based on a liquid PbBi (LBE) cooled fast reactor (80 MWth) which may be operated in both critical and subcritical modes. In the latter case the core is fed by spallation neutrons obtained from a 600 MeV proton beam hitting the LBE coolant/target. The accelerator providing this beam is a high intensity CW superconducting linac which is laid out for the highest achievable reliability. The combination of a parallel redundant and of a fault tolerant scheme should allow obtaining an MTBF value in excess of 250 hours that is required for optimal integrity and successful operation of the ADS. Myrrha is expected to be operational in 2023. The forthcoming 4-year period is fully dedicated to R&D activities, and in the field of the accelerator they are strongly focused on the reliability aspects and on the proper shaping of the beam trip spectrum.
Development of fragmented low-Z ion beams for the NA61 fixed-target experiment at the CERN SPS
(2011)
The NA61 experiment, aims to study the properties of the onset of deconfinement at low SPS energies and to find signatures of the critical point of strongly interacting matter. A broad range in T-μB phase diagram will be covered by performing an energy (13A-158A GeV/c) and system size (p+p, Be+Be, Ar+Ca, Xe+La) scan. In a first phase, fragmented ion beams of 7Be or 11C produced as secondaries with the same momentum per nucleon when the incident primary Pb-ion beam hits a thin Be target will be used. The H2 beam line that transports the beam to the experiment acts as a double spectrometer which combined with a new thin target (degrader) where fragments loose energy proportional to the square of their charge allows the separation of the wanted A/Z fragments. Thin scintillators and TOF measurement for the low energy points are used as particle identification devices. In this paper results from the first test of the fragmented ion beam done in 2010 will be presented showing that a pure Be beam can be obtained satisfying the needs of the experiment.
Space charge lenses using a stable electron cloud for focusing low energy heavy ion beams are an alternative concept to conventional ion optics. Due to external fields electrons are confined inside the lens’ volume. In case of a homogeneously distributed electron cloud the linear electric space charge field enables beam focusing free of aberration. Since the mapping quality of the lens is related to the confinement, non-destructive diagnostics has been developed to determine the plasma parameters and to characterize the collective behavior of the confined nonneutral plasma. Moreover, a scaled up space charge lens was constructed for a detailed investigation of the nonneutral plasma properties as well as beam interactions with a stable confined electron cloud. Experimental results will be presented in comparison with numerical simulations.
As the successor of the EUROTRANS project, the MAX project is aiming to continue the R&D effects for a European Accelerator-Driven System and to bring the conceptual design to reality. The layout of the driver linac for MAX will follow the reference design made for the XT-ADS phase of the EUROTRANS project. For the injector part, new design strategies and approaches, e.g. half resonant frequency, half transition-energy between the RFQ and the CH-DTL, and using the 4-rod RFQ structure instead of the originally proposed 4-vane RFQ, have been conceived and studied to reach a more reliable CW operation at reduced costs. In this paper, the design and simulation results of the MAX injector are presented.
MYRRHA is conceived as an accelerator driven system (ADS) for transmutation of high level nuclear waste. The neutron source is created by coupling a proton accelerator of 600 MeV with a 4 mA proton beam, a spallation source and a sub-critical core. The IAP of Frankfurt University is responsible for the development of the 17 MeV injector operated at 176 MHz. The injector consists of a 1.5 MeV 4-Rod-RFQ and six CH-drifttube-structures. The first two CH-structures will be operated at room temperature and the other CH-structures are superconducting cavities assembled in one cryo-module. To achieve the extremely high reliability required by the ADS application, the design of the 17 MeV injector has been intensively studied, with respect to thermal issues, minimum peak fields and field distribution.
Chromatic, geometric and space charge effects on laser accelerated protons focused by a solenoid
(2011)
We studied numerically emittance and transmission effects by chromatic and geometric aberrations, with and without space charge, for a proton beam behind a solenoid in the laser proton experiment LIGHT at GSI. The TraceWin code was employed using a field map for the solenoid and an initial distribution with exponential energy dependence close to the experiment. The results show a strong effect of chromatic, and a relatively weak one of geometric aberrations as well as dependence of proton transmission on distance from the solenoid. The chromatic effect has an energy filtering property due to the finite radius beam pipe. Furthermore, a relatively modest dependence of transmission on space charge is found for p production intensity below 1011.
Experimental results and theoretical predictions in laser acceleration of protons achieved energies of ten to several tens of MeV. The LIGHT project (Laser Ion Generation, Handling and Transport) is proposed to use the PHELIX laser accelerated protons and to provide transport, focusing and injection into a conventional accelerator. This study demonstrates transport and focusing of laser-accelerated 10 MeV protons by a pulsed 18 T magnetic solenoid. The effect of co-moving electrons on the beam dynamics is investigated. The unique features of the proton distribution like small emittances and high yield of the order of 1013 protons per shot open new research area. The possibility of creating laser based injectors for ion accelerators is addressed. With respect to transit energies, direct matching into DTL's seems adequate. The bunch injection into a proposed CH− structure is under investigation at IAP Frankfurt. Options and simulation tools are presented.
An optimized design of a stellarator-type storage ring for low energy ion beams was numerically investigated. The magnetic field variation along the circumference and therefore magnetic heating is suppressed by using simple circular correction coils. Particle-in-Cell (PIC) simulations in a magnetic flux coordinate system show the ability of high current ion beam accumulation in such a configuration with unique features for clockwise and anticlockwise moving beams. Additionally scaled down experiments with two 30 degree room temperature toroidal segments were performed to demonstrate toroidal transport and to develop optical beam diagnostics. Properties of multi-component beams, redistribution of transversal momenta in the non-adiabatic part of the experimental configuration and investigation of strongly confined beam induced electron clouds will be addressed.
For the research program with cooled antiprotons at FAIR a dedicated 70 MeV, 70 mA proton injector is required. The main acceleration of this room temperature linac will be provided by six CH cavities operated at 325 MHz. Each cavity will be powered by a 2.5 MW Klystron. For the second acceleration unit from 11.5 MeV to 24.2 MeV a 1:2 scaled model has been built. Low level RF measurements have been performed to determine the main parameters and to prove the concept of coupled CH cavities. For this second tank technical and mechanical investigations have been performed in 2010 to develop a complete technical concept for the manufacturing. In Spring 2011, the construction of the first power prototype has started. The main components of this cavity will be ready for measurements in summer 2011. At that time, the cavity will be tested with a preliminary aluminum drift tube structure, which will allow precise frequency and field tuning. This paper will report on the recent technical development and achievements. It will outline the main fabrication steps towards that novel type of proton DTL. Also first low level RF measurements are expected.
The MYRRHA Project (Multi Purpose Hybrid Reactor for High Tech Applications) at Mol/belgium will be a user facility with emphasis on research with neutron generated by a spallation source. One main aspect is the demonstration of nuclear waste technology using an accelerator driven system. A superconducting linac delivers a 4 mA, 600 MeV proton beam. The first accelerating section is covered by the 17 MeV injector. It consists of a proton source, an RFQ, two room temperature CH cavities and 4 superconducting CH-cavities. The initial design has used an RF frequency of 352 MHz. Recently the frequency of the injector has been set to 176 MHz. The main reason is the possible use of a 4-rod-RFQ with reduced power dissipation and energy, respectively. The status of the overall injector layout including cavity design is presented.
SIS100 is the main synchrotron of the FAIR project. It is designed to accelerate high intensity intermediate charge state uranium beams from 200 MeV/u up to 2.7 GeV/u. Intermediate charge state heavy ions are exposed to a high probability of charge exchange due to collisions with residual gas molecules. Since the charge exchange process changes the magnetic rigidity, the involved ions are lost behind dispersive elements, and an energy-dependent gas desorption takes place. The StrahlSim code has been used to predict the stability of the residual gas pressure in SIS100 under beam loss driven dynamic conditions. The results show, that a stable operation at highest U28+ intensities is possible, under the constraint that the vacuum chambers of the ion catcher system are cold enough to pump hydrogen. Furthermore, in order to determine the load to the cryogenic system, the average beam energy deposition onto the ion catcher system has been calculated.
The ARMADILLO bunch compressor currently being designed at IAP is capable of reaching a longitudinal pulse compression ratio of 45 for proton beams of 150 mA at 2 MeV. It will provide one nanosecond proton pulses with a peak current of 7.7 A. The system guides nine linacμbunches deflected by a 5 MHz rf kicker and uses four dipole magnets - two homogeneous and two with field gradients - to merge them on the target. For longitudinal focusing and an energy variation of ±200 keV two multitrack rf cavities are included. ARMADILLO will be installed at the end of the Frankfurt Neutron Source FRANZ making use of the unique 250 kHz time structure. This contribution will provide an overview of the layout of the system as well as recent advances in component design and beam dynamics of the compressor.
At the Institute for Applied Physics (IAP), University of Frankfurt, a s.c. 325 MHz CH-Cavity is under development for future beam tests at GSI UNILAC, Darmstadt. The cavity with 7 accelerating cells has a geometrical beta of 0.15 corresponding to 11.4 AMeV. The design gradient is 5 MV/m. The geometry of this resonator was optimized with respect to a compact design, low peak fields, surface processing, power coupling and tuning. Furthermore a new tuning system based on bellow tuners inside the resonator will control the frequency during operation. After rf tests in Frankfurt the cavity will be tested with a 10 mA, 11.4 AMeV beam delivered by the GSI UNILAC. In this paper rf simulations, multipacting analysis as well as thermal calculations will be presented.
The SIS300 synchrotron, planned for the new Facility for Antiproton and Ion Research (FAIR) at GSI-Darmstadt, will become the first superconducting synchrotron worldwide using cos(θ) magnets for resonant slow extraction. A multi-objective optimization algorithm has been developed for the design of the non-linear magnet scheme. The optimization algorithm makes use of the analytical model for the slow extraction from Kobayashi, the analytical description of the resonance excitation and amplitude-dependent tune-shift from Bengtsson, and corrects the chromaticity in order to fulfill the Hardt condition. As a result, the placement of the chromatic and harmonic sextupole magnets in SIS300, the number of sextupole families and the gradients of these families have been optimized for a high efficiency slow extraction. The algorithm accounts also for the sextupole errors on the dipole magnets, compensating its effects. Furthermore, optimized time-dependent settings for the sextupole magnets are generated to compensate the persistent current decay occurring at slow extraction. Tolerances for the magnets are set for the limits where the compensation is no longer valid.
Chopper systems are used to pulse charged particle beams. In most cases, electric deflection systems are used to generate beam pulses of defined lengths and appropriate repetition rates. At high beam intensities, the field distribution of the chopper system needs to be adapted precisely to the beam dynamics in order to avoid aberrations. An additional challenge is a robust design which guarantees reliable operation. For the Frankfurt Neutron Source FRANZ, an E×B chopper system is being developed which combines static magnetic deflection with a pulsed electric field in a Wien filter configuration. It will generate proton pulses with a flat top of 50 ns at a repetition rate of 250 kHz for 120 keV, 200 mA beams. For the electric deflection, pre-experiments with static and pulsed fields were performed using a helium ion beam. In pulsed mode operation, ion beams of different energies were deflected with voltages of up to ±6 kV and the resulting response was measured using a beam current transformer. A comparison between experiments and theoretical calculations as well as numerical simulations are presented.
A modern linear accelerator of ions is a long chain of different accelerating-focusing structures. The design of new linacs, as well as an upgrade and optimization of operating facilities, requires precise and reliable beam matching with the subsequent sections. Proper matching of the beam to the channel allows to improve the performance of the whole linac and to reduce the specific costs. Additionally it helps to avoide particle loss in high energy high intensity linacs. Generally a matching algorithm combines precisely measured or calculated accelerating-focusing external fields and experimentally obtained details of the beam parameters with an advanced code for beam dynamics simulations including space charge effects. Experimental results are introduced into a code as input data. The described algorithm has already been successfully implemented for several GSI projects: an upgrade of the GSI heavy ion linac UNILAC, an ion linac for the cancer therapy, the proton linac for the FAIR facility, a facility for laser acceleration of ions and others. Measured data and results of beam dynamics simulations leading to an achieved improvement of the linac performance are presented.
At GSI a new, superconducting (sc) continuous wave (cw) LINAC is under design in cooperation with the Institute for Applied Physics (IAP) of Frankfurt University and the Helmholtz Institut Mainz (HIM). This proposed LINAC is highly requested by a broad community of future users to fulfill the requirements of nuclear chemistry, nuclear physics, and especially in the research field of Super Heavy Elements (SHE). In this context the preliminary layout of the LINAC has been carried out by IAP. The main acceleration of up to 7.3 AMeV will be provided by nine sc Crossbar-H-mode (CH) cavities operated at 217 MHz. Currently, a prototype of the cw LINAC as a demonstrator is under development. The demonstrator comprises a sc CH-cavity embedded between two sc solenoids mounted in a horizontal cryomodule. A full performance test of the demonstrator in 2013/14 by injecting and accelerating a beam from the GSI High Charge Injector (HLI) is one important milestone of the project. The status of the demonstrator is presented.
The superconducting CH-structure (Crossbar-H-mode) is a multi-cell drift tube cavity for the low and medium energy range operated in the H21-mode, which has been developed at the Institute for Applied Physics (IAP) of Frankfurt University. With respect to different high power applications two types of superconducting CH-structures (f = 325 MHz, β = 0.16, seven cells and f = 217 MHz, β = 0.059, 15 cells) are presently under construction and accordingly under development. The structural mechanical simulation is a very important aspect of the cavity design. Furthermore, several simulations with ANSYS Workbench have been performed to predict the deformation of the cavity walls due to the cavity cool-down, pressure effects and mechanical vibrations. To readjust the fast frequency changes in consequence of the cavity shape deformation, a new concept for the dynamic frequency tuning has been investigated, including a novel type of bellow-tuner.
The Frankfurt Neutron Source at the Stern-Gerlach-Zentrum is driven by a 2 MeV proton linac consisting of a 4-rod-radio-frequency-quadrupol (RFQ) and an 8 gap IH-DTL structure. RFQ and IH cavity will be powered by only one radio frequency (RF) amplifier to reduce costs. The RF-amplifier of the RFQ-IH combination is coupled into the RFQ. Internal inductive coupling along the axis connects the RFQ with the IH cavity ensuring the required power transition as well as a fixed phase relation between the two structures. The main acceleration of 120 keV up to 2.03 MeV will be reached by the RFQ-IH combination with 175 MHz and at a total length of 2.3 m. The losses in the RFQ-IH combination are about 200 kW.
This novel kind of neutron beam facility will provide 1 ns short neutron pulses with an approximately thermal energy distribution around 30 keV. The pulse repetition rate will be up to 250 kHz, the total proton number per pulse will be up to 6×1010 in the final stage, starting with a p – source current of 200 mA. A second target station will allow n – activation experiments by cw beam operation. An intense 2 MeV proton beam will drive a neutron source by the 7 Li (p,n) 7 Be reaction. The facility is under construction at the physics experimental hall of the J.W. Goethe – University. The 1m thick concrete tunnel was installed in 2009. In 2011 all rf amplifiers will be delivered and installed. Successful 200 mA proton source experiments in 2010 at a test stand will be followed by experiments on the 120 kV FRANZ terminal in 2011. The 250 kHz, 100 ns chopper in front of the rf linac is under construction, while the 2 MeV bunch compressor design was finished and the technical design of all components has started. The main accelerator cavity is under construction. First 2 MeV beam tests are expected for end of 2012.
Mit dieser Arbeit konnte die Funktionsweise von gekoppelten Resonatoren erklärt werden. Das Verhalten von induktiv gekoppelten Beschleunigerkavitäten wurde näher studiert. Dabei wurde verstanden, wie sich Verstimmungen auf die Resonatoren auswirken und was zu tun ist um die Spannungsamplituden des gekoppelten Systems zu beeinflussen. Zudem wurden die Grundlagen für den gekoppelten Betrieb des FRANZ-Beschleunigers gelegt.
This work is dedicated to the study of the vector and axial vector spectral functions of the τ lepton within the framework of a U(2)L × U(2)R Linear Sigma Model with electroweak interaction. As an effective field theory the Linear Sigma Model describes hadronic degrees of freedom based on the symmetries of the Standard Model. Therefore, the following section aims at giving a very general and concise introduction to the Standard Model and the meaning of symmetries for contemporary elementary particle physics. In the next section the SU(3)C symmetry group will be discussed in short, followed by an introduction to chiral symmetry SU(2)L × SU(2)R. In the last section of this chapter the Glashow-Weinberg-Salam theory of the local group SU(2)L × U(1)Y is presented. Important concepts of the theoretical framework of the Standard Model, such as the Noether Theorem, the Gauge Principle, Spontaneous Symmetry Breaking, and the Higgs Mechanism will be introduced in the context of these three symmetry groups. In Chapter 2 it will be first shown how the symmetries of the Standard Model are realised within the global U(2)L × U(2)R Linear Sigma Model and how electroweak interactions can be introduced to the model on the basis of local SU(2)L × U(1)Y symmetry transformations of the hadronic degrees of freedom. The vertices that are relevant for the vector and axial vector decay channels in weak τ decay are extracted from the Lagrangian with electroweak interaction in Chapter 3. This is followed by a short introduction to the Källen-Lehmann Representation of spectral functions and how these can be parametrised within the framework of this model (Chapter 4). The results of the vector and axial vector spectral functions are presented in Chapter 5 and 6.
Neutroneneinfangquerschnitte werden häufig mithilfe der Aktivierungsmethode bestimmt. Hierbei wird die zu untersuchende Probe mit Neutronen der gew¨unschten Energie bestrahlt und danach in einem untergrundoptimierten Labor ausgezählt. Am Institut für Angewandte Physik der Goethe Universität Frankfurt wurde ein solcher Aufbau realisiert. Er besteht aus zwei Clover Detektoren, die gegenüberliegend in enger Geometrie angeordnet sind. Die aktivierte Probe wird mittels spezieller Probenhalter reproduzierbar und zentriert zwischen den Detektoren platziert. Die Clover Detektoren sind mit passiven Schilden (Pb) und einer aktiven Abschirmung (BGO) umgeben. Die unterschiedlichen Abschirmungen wirken sich in verschieden Energiebereichen jeweils anders aus.
Diese Arbeit befasst sich mit der astrophysikalischen Motivation und dem Aufbau, mit dem später die Ausbeute einer neutronenaktivierten Probe bestimmt werden kann. Außerdem werden die Ergebnisse der verschiedenen Untergrundmessungen miteinander verglichen.