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The knowledge of the build up time of space charge compensation (SCC) and the investigation of the compensation process is of main interest for low energy beam transport of pulsed high perveance ion beams under space charge compensated conditions. To investigate experimentally the rise of compensation an LEBT system consisting of a pulsed ion source, two solenoids and a drift tube as diagnostic section has been set up. The beam potential has been measured time resolved by a residual gas ion energy analyser (RGA). A numerical simulation for the calculation of self-consistent equilibrium states of the beam plasma has been developed to determine plasma parameters which are difficult measure directly. The results of the simulation has been compared with the measured data to investigate the behavior of the compensation electrons as a function of time. The acquired data shows that the theoretical rise time of space charge compensation is by a factor of two shorter than the build up time determined experimentally. In view of description the process of SCC an interpretation of the gained results is given.
For investigation of space charge compensation process due to residual gas ionization and the experimentally study of the rise of compensation, a Low Energy Beam Transport (LEBT) system consisting of an ion source, two solenoids, a decompensation electrode to generate a pulsed decompensated ion beam and a diagnostic section was set up. The potentials at the beam axis and the beam edge were ascertained from time resolved measurements by a residual gas ion energy analyzer. A numerical simulation of self-consistent equilibrium states of the beam plasma has been developed to determine plasma parameters which are difficult to measure directly. The temporal development of the kinetic and potential energy of the compensation electrons has been analyzed by using the numerically gained results of the simulation. To investigate the compensation process the distribution and the losses of the compensation electrons were studied as a function of time. The acquired data show that the theoretical estimated rise time of space charge compensation neglecting electron losses is shorter than the build up time determined experimentally. To describe the process of space charge compensation an interpretation of the achieved results is given.
Accelerating cavities exchange HOM power through interconnecting beam pipes in case of signal frequencies above the cut-off of their propagating waveguide modes. This may lead either to improved HOM damping or - in the case most severe - to unwanted phase coherence of fields to the beam. Therefore the knowledge of the scattering properties of a cavity as a line element is needed to analyse all kinds of RF cavity-cavity interaction. Since there is a lack of measurement tools capable to provide a multidimensional scattering matrix at a given frequency point, we have been developing a method for this purpose. It uses a set of 2-port S-parameters of the device under test, embedded in a number of geometrically different RF environments. The application of the method is demonstrated with copper models of TESLA cavities.
To preserve the required beam quality in an e+/e- collider it is necessary to have a very precise beam position control at each accelerating cavity. An elegant method to avoid additional length and beam disturbance is the usage of signals from existing HOM-dampers. The magnitude of the displacement is derived from the amplitude of a dipole mode whereas the sign follows from the phase comparison of a dipole and a monopole HOM. To check the performance of the system, a measurement setup has been built with an antenna which can be moved with micrometer resolution to simulate the beam. Furthermore we have developed a signal processing to determine the absolute beam displacement. Measurements on the HOM-damper cell can be done in the frequency domain using a network analyser. Final measurements with the nonlinear time dependent signal processing circuit has to be done with very short electric pulses simulating electron bunches. Thus, we have designed a sub nanosecond pulse generator using a clipping line and the step recovery effect of a diode. The measurement can be done with a resolution of about 10 micrometers. Measurements and numerical calculations concerning the monitor design and the pulse generator are presented.
To fulfil the requirements of ESS on beam transmission and emittance growth a detailed knowledge of the physics of beam formation as well as the interaction of the H- with the residual gas is substantial. Space charge compensated beam transport using solenoids for ion optics is in favour for the Low Energy Beam Transport (LEBT) between ion source and the first RFQ. Space charge compensation reduces the electrical self fields and beam radii and therefore emittance growth due to aberrations and redistribution. Transport of H- near the ion source is negatively influenced by the dipole fields required for beam extraction and e--dumping and the high gas pressure. The destruction of the rotational symmetry together with the space charge forces causes emittance growth and particle losses within the extraction system. High residual gas pressure near the extractor together with the high cross section for stripping will influence the transmission as well as space charge compensation. Therefore a detailed knowledge of the interaction of the residual gas with the beam and the influence of the external fields on the distribution of the compensation particles is necessary to reduce particle losses and emittance growth. Preliminary experiments using positive hydrogen ions for reference already show the influence of dipole fields on beam emittance. First measurements with H- confirm these results. Additional information on the interactions of the residual gas with the beam ions have been gained from the measurements using the momentum and energy analyser.
A LEBT system consisting of an ion source, two solenoids, and a diagnostic section has been set up to investigate the space charge compensation process due to residual gas ionization [1] and to study experimentally the rise of compensation. To gain the radial beam potential distribution time resolved measurements of the residual gas ion energy distribution were carried out using a Hughes Rojanski analyzer [2,3]. To measure the radial density profile of the ion beam a CCD-camera performed time resolved measurements, which allow an estimation the rise time of compensation. Further the dynamic effect of the space charge compensation on the beam transport was shown. A numerical simulation under assumption of selfconsistent states [4] of the beam plasma has been used to determine plasma parameters such as the radial density profile and the temperature of the electrons. The acquired data show that the theoretical estimated rise time of space charge compensation neglecting electron losses is shorter than the build up time determined experimentally. An interpretation of the achieved results is given.
Für Romanisten ist Interkomprehension seit der Begründung ihrer Disziplin ein Anliegen, für romanischsprachige Menschen ist sie meist ein persönliches Erlebnis der partiellen Entdeckung, vor 1500 Jahren war sie alltägliche Realität. Es geht um die Fähigkeit, in einer Gruppe von Sprachen, die einen gemeinsamen Ursprung haben, kommunizieren zu können.
Läßt man die Problematik der bei dieser Aussage verwendeten Ausdrücke außer Betracht und schränkt den Blickwinkel auf die Gruppe der romanischen Sprachen ein, so lassen sich eine Reihe von Aussagen über Interkomprehension machen.
Daß zwischen dem sechsten und achten Jahrhundert, also während der protoromanischen Phase, Interkomprehension zwischen entfernten Gegenden des niedergegangen Imperium Romanum möglich war, ist unstrittig, freilich gab es keine außersprachlichen Gründe, die das Faktum Interkomprehension in den Vordergrund hätten rücken können. Die einzig übriggebliebene Zentralmacht Kirche benutzte ihr eigenes Latein. ...
Der sprachfamilienbezogene Erwerb einer L3 bis Lx hat durch die jüngeren sprachpolitischen Forderungen der Europäischen Kommission 1997 entscheidenden Auftrieb erhalten. Im Livre Blanc sur l´éducation et la formation von 1995 bilanziert die Europäische Kommission das Ergebnis der fremdsprachlichen Bemühungen der großen Flächenstaaten der Union als eher kümmerlich und fordert eine Wende. Künftig soll eine Europäische Mehrsprachigkeit drei Perspektiven aufweisen: eine differenzierte Betrachtung von Kompetenzen (rezeptive Mehrsprachigkeit), die Ermöglichung des gezielten Erwerbs von Teilkompetenzen mit modularen Aufbaumöglichkeiten (fachsprachlicher approach zur rezeptiven Lesekompetenz) und das Nutzen der Verwandtschaftsbeziehungen zwischen Sprachen (u.a. romanische Interkomprehensionsforschung). Diese drei Perspektiven werden in dem dreigliedrigen Projekt zur "Eurocomprehension" der Universität Frankfurt zusammengefaßt. Der Frankfurter Beitrag bezieht sich auf die Gruppe der romanischen Sprachen. ...
Investigation of the focus shift due to compensation process for low energy ion beam transport
(2000)
In magnetic Low Energy Beam Transport (LEBT) sections space charge compensation helps to enhance the transportable beam current and to reduce emittance growth due to space charge forces. For pulsed beams the time neccesary to establish space charge compensation is of great interest for beam transport. Particularly with regard to beam injection into the first accelerator section (e.g. RFQ) investigation of effects on shift of the beam focus due to space charge compensation are very important. The achieved results helps to obviate a mismatch into the first RFQ. To investigate the space charge compensation due to residual gas ionization, time resolved measurements using pulsed ion beams were performed at the LEBT system at the IAP and at the CEA-Saclay injektion line. A residual gas ion energy analyser (RGIA) equiped with a channeltron was used to measure the potential destribution as a function of time to estimate the rise time of compensation. For time resolved measurements (delta t min=50ns) of the radial density profile of the ion beam a CCD-camera was applied. The measured data were used in a numerical simulation of selfconsistant eqilibrium states of the beam plasma [1] to determine plasma parameters such as the density, the temperature, the kinetic and potential energy of the compensation electrons as a function of time. Measurements were done using focused proton beams (10keV, 2mA at IAP and 92keV, 62mA at CEA-Saclay) to get a better understanding of the influence of the compensation process. An interpretation of the acquired data and the achieved results will be presented.
The determination of the beam emittance using conventional destructive methods suffers from two main disadvantages. The interaction between the ion beam and the measurement device produces a high amount of secondary particles. Those particles interact with the beam and can change the transport properties of the accelerator. Particularly in the low energy section of high current accelerators like proposed for IFMIF, heavy ion inertial fusion devices (HIDIF) and spallation sources (ESS, SNS) the power deposited on the emittance measurement device can lead to extensive heat on the detector itself and can destruct or at least dejust the device (slit or grit for example). CCD camera measurements of the incident light emitted from interaction of beam ions with residual gas are commonly used for determination of the beam emittance. Fast data acquisition and high time resolution are additional features of such a method. Therefore a matrix formalism is used to derive the emittance from the measured profile of the beam [1,2] which does not take space charge effects and emittance growth into account. A new method to derive the phase space distribution of the beam from a single CCD camera image using statistical numerical methods will be presented together with measurements. The results will be compared with measurements gained from a conventional Allison type (slit-slit) emittance measurement device.
Influence of space charge fluctuations on the low energy beam transport of high current ion beams
(2000)
For future high current ion accelerators like SNS, ESS or IFMIF the beam behaviour in low energy beam transport sections is dominated by space charge forces. Therefore space charge fluctuations (e. g. source noise) can drastically influence the beam transport properties of the low energy beam transport section. Losses of beam ions and emittance growth are the most severe problems. For electrostatic transport systems either a LEBT design has to be found which is insensitive to variations of the space charge or the origin of the fluctuations has to be eliminated. For space charge compensated transport as proposed for ESS and IFMIF the situation is different: No major influence on beam transport is expected for fluctuations below a cut-off frequency given by the production rate of the compensation particles. Above this frequency the fluctuations can not be compensated by particle production alone, but redistributions of the compensation particles helps to compensate the influence of the fluctuations. Above a second cut-off frequency given by the density and the temperature of the compensation particles their redistribution is too slow to reduce the influence of the space charge fluctuations. Transport simulations for the IFMIF injector including space charge fluctuations will be presented together with a determination of the cut-off frequencies. The results will be compared with measurements of the rise time of space charge compensation.
The operation of a Free Electron Laser (FEL) in the ultraviolet or in the X-ray regime requires the acceleration of electron bunches with an rms length of 25 to 50 mikrometer. The wakefields generated by these sub picosecond bunches extend into the frequency range well beyond the threshold for Cooper pair breakup (about 750 GHz) in superconducting niobium at 2 K. It is shown, that the superconducting cavities can indeed be operated with 25 mikrometer bunches without suffering a breakdown of superconductivity (quench), however at the price of a reduced quality factor and an increased heat transfer to the superfluid helium bath. This was first shown by wakefield calculations based on the diffraction model [1]. In the meantime a more conventional method of computing wake fields in the time domain by numerical methods was developed and used for the wakefield calculations [2]. Both methods lead to comparable results: the operation of TESLA with 25 mikrometer bunches is possible but leads to an additional heat load due to the higher order modes (HOMs). Therefore HOM dampers for these high frequencies are under construction [3]. These dampers are located in the beam pipes between the 9-cell cavities. So it is of interest, if there are trapped modes in the cavity due to closed photon orbits. In this paper we investigate the existence of trapped modes and the distribution of heat load over the surface of the TESLA cavity by numerical photon tracking.
"Eurocomprehension" is the term used to describe European intercomprehension in Europe’s three major language families, the Romance, the Slavic and the Germanic. The aim of eurocomprehension is to achieve multilingualism conforming to EU language policy goals through the entry-point of receptive competence in a modular structure. Linguistic intercomprehension research forms the transfer bases for the cognitive use of relations between the language groups which didactics of multilingualism implement. ...
Le concept d’eurocompréhension signifie intercompréhension dans les trois grands groupes linguistiques européens, à savoir les langues romanes, slaves et germaniques. Il s’agit, en respectant les objectifs1 de la politique linguistique de l’Union Européenne, de parvenir de façon modulaire au plurilinguisme par le biais de compétences réceptives. Dans ce cadre, les recherches linguistiques effectuées sur l’intercompréhension fournissent les bases de transfert interlangues pour l’exploitation cognitive de la parenté entre les langues des groupes différents. ...
Rezeptive Mehrsprachigkeit ist eine der jüngsten Forderungen der EU-Kommission zum Erreichen einer realistischen Mehrsprachigkeit in Europa. Die maximalistischen Forderungen nach Perfektion in allen sprachlichen Kompetenzen haben sich in den nationalen Unterrichtswesen als illusionär erwiesen, da diese nirgendwo von statistisch nachvollziehbarem Erfolg gekrönt sind. Die sprachliche Diversität im multilingualen Europa findet sich nicht in der Realität der Bildungssysteme wieder. Zwar verfügen heute europaweit 26 % der Europäer über eine zweite und 8% über eine dritte Fremdsprache, in den einzelnen Ländern sieht es jedoch oft desolat aus. Während in den kleineren Unionsländern kaum jemand als nur monolingual gilt (Luxemburg 2%) ist die Krankheit der Einsprachigkeit in den großen EU-Staaten seuchenhaft verbreitet, etwa Großbritannien mit 66%. Dies hat in den neunziger Jahren in der Kommission zu den Postulaten geführt, die sich die Forschergruppe EuroCom als Programm gesetzt hat, nämlich Mehrsprachigkeit über den Einstieg in rezeptive Kompetenzen modularisiert und kognitiv über Transferbasen innerhalb von Sprachfamilien zu erreichen. EuroCom steht dabei als Kürzel für Eurocomprehension, ein Akronym für Europäische Interkomprehension in den drei großen Sprachengruppen Europas, der romanischen, slawischen und germanischen. Die Beschränkung auf rezeptive Kompetenzen ist dabei nur ein methodisches Ausgangsprinzip, das es ermöglicht, Mehrsprachigkeit besonders schnell über das Leseverständnis zu erreichen und modularisiert auf Hörverständnis und aktive Sprechkompetenz sukzessiv auszuweiten. Die Methode EuroCom arbeitet über die Aktivierung intralingualen Wissens mit linguistischem Transfermaterial in nahverwandten Sprachen, das als kognitives Potential den Erschließungsprozess optimiert und in kürzester Zeit ein Lese- und Hörverstehen in einer ganzen Sprachenfamilie erreichbar macht. ...
Der Begriff Eurocomprehension steht für Europäische Interkomprehension in den drei großen Sprachengruppen Europas, der romanischen, slawischen und germanischen. Es geht der Eurocomprehension darum, unter EU-konformen sprachpolitischen Zielsetzungen Mehrsprachigkeit über den Einstieg in rezeptive Kompetenzen modularisiert zu erreichen. Dabei liefert die linguistische Interkomprehensionsforschung die interlingualen Transferbasen zur kognitiven Nutzung von Verwandtschaftsbeziehungen in Sprachgruppen, die eine Mehrsprachigkeitsdidaktik umsetzt. ...
The crossbar-H-mode (CH) structure is the first superconducting multicell drift tube cavity for the low and medium energy range operated in the H21 mode. Because of the large energy gain per cavity, which leads to high real estate gradients, it is an excellent candidate for the efficient acceleration in high power proton and ion accelerators with fixed velocity profile. A prototype cavity has been developed and tested successfully with a gradient of 7MV/m. A few new superconducting CH cavities with improved geometries for different high power applications are under development at present. One cavity (f=325 MHz, β=0.16, seven cells) is currently under construction and studied with respect to a possible upgrade option for the GSI UNILAC. Another cavity (f=217 MHz, β=0.059, 15 cells) is designed for a cw operated energy variable heavy ion linac application. Furthermore, the EUROTRANS project (European research program for the transmutation of high level nuclear waste in an accelerator driven system, 600 MeV protons, 352 MHz) is one of many possible applications for this kind of superconducting rf cavity. In this context a layout of the 17 MeV EUROTRANS injector containing four superconducting CH cavities was proposed by the Institute for Applied Physics (IAP) Frankfurt. The status of the cavity development related to the EUROTRANS injector is presented.
EUROTRANS is a European research program for the transmutation of high level nuclear waste in an accelerator-driven system (ADS). As proposed, the driver linac needs to deliver a 2.5–4 mA, 600 MeV continuous-wave (CW) proton beam and later a 20 mA, 800 MeV one to the spallation target in the prototype-scale and industrial-scale demonstration phases, respectively. This paper is focusing on the conceptual studies performed with respect to the 17 MeV injector. First, the special beam dynamics strategies and methods, which have been developed and applied to design a current-variable injector up to 30 mA for allowing an easy upgrade without additional R&D costs, will be introduced. Then the error study made for evaluating the tolerance limits of the designed injector will be presented as well.
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.