Extraction and low energy transport of negative ions

High perveance negative ion beams with low emittance are essential for several next generation particle accelerators (i. g. spallation sources like ESS [1] and SNS [2]). The extraction and transport of these beams have intrinsic difficulties different from positive ion beams. Limitation of beam current and emittance growth have to be avoided. To fulfill the requirements of those projects a detailed knowledge of the physics of beam formation the interaction of the H- with the residual gas and transport is substantial. A compact cesium free H- volume source delivering a low energy high perveance beam (6.5 keV, 2.3 mA, perveance K= 0.0034) has been built to study the fundamental physics of beam transport and will be integrated into the existing LEBT section in the near future. First measurements of the interaction between the ion beam and the residual gas will be presented together with the experimental set up and preliminary results

Influence of space charge fluctuations on the low energy beam transport of high current ion beams

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

Study of compensation process of ion beams

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

Time-resolved investigation of the compensation process of pulsed ion beams

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

Non destructive determination of beam emittance for low energy ion beams using CCD camera measurements

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

Investigation of the rise of compensation of high perveance ion beams using a time-resolving ion energy spectrometer

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

Investigation of the focus shift due to compensation process for low energy ion beam transport

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

Zivilgesellschaft

Zivilgesellschaft ist eine gesellschaftliche Sphäre jenseits des Staates, jedoch nicht des Politischen. Deren Akteure befinden sich in einem intermediären Raum der Öffentlichkeit zwischen Staat, Wirtschaft und Privatsphäre. Der Beitrag skizziert ideengeschichtliche Hintergründe und die aktuelle gesellschaftspolitische Konjunktur des Begriffs

Der Diskurs der Zivilgesellschaft

"In einem ersten Schritt gibt der Autor einen kurzen Überblick über die politischen Kontexte des neueren Begriffsgebrauchs von Zivilgesellschaft. In einem zweiten Schritt werden demokratietheoretische Konzeptionen der Zivilgesellschaft im Überblick dargestellt. Auf die Begriffsverwendung in den jüngsten reformpolitischen Diskussionen macht die abschließende kurze Skizze zu 'Bürgerengagement und Zivilgesellschaft' aufmerksam. Der Diskurs der Zivilgesellschaft lässt sich insgesamt als eine weit ausholende und unabgeschlossene theoretische Suchbewegung nach den politischen Handlungsmöglichkeiten gesellschaftlicher Akteure zur Herstellung und Fortentwicklung demokratischer Formen der Politik charakterisieren. Assoziationen im intermediären Raum der Politik, politische Öffentlichkeit und responsive politische Institutionen einerseits, rechtsstaatliche Garantien negativer und positiver Freiheit andererseits bilden die Grundpfeiler des Diskurses. Seine Dynamik erhält er im Kontext der politischen Selbstverständigung radikaldemokratischer Akteure. Im Mittelpunkt steht hier der Zusammenhang einer Reformpolitik, die die Möglichkeiten der politischen Beteiligung zivilgesellschaftlicher Akteure an politischer Meinungs-, Willens- und Entscheidungsfindung zu erweitern sucht, mit einer demokratischen Selbstbegrenzung der Akteure auf den - für weitere Demokratisierung offen stehenden - institutionellen Rahmen liberaler Demokratie. Geprägt sind diese Selbstverständigungsdiskurse durch zwei Ausgangspunkte: den kulturellen Pluralismus auf der einen, die Komplexität einerausdifferenzierten modernen Gesellschaft und die kolonialisierenden Effekte von Markt und Staat auf der anderen Seite." (Autorenreferat