Comparison of Enamel and Stainless Steel Electron Cloud Clearing Electrodes Tested in the CERN Proton Synchrotron

During the 2007 run with the nominal LHC proton beam, electron cloud has been clearly identified and characterized in the PS using a dedicated setup with shielded button-type pickups. Efficient electron cloud suppression could be achieved with a stainless steel stripline-type electrode biased to negative and positive voltages up to ± 1 kV. For the 2008 run, a second setup was installed in straight section 84 of the PS where the stainless steel was replaced by a stripline composed of an enamel insulator with a resistive coating. In contrast to ordinary stripline electrodes this setup presents a very low beam coupling impedance and could thus be envisaged for long sections of high-intensity machines. Here, we present first comparative measurements with this new type of enamel clearing electrode using the nominal LHC beam with 72 bunches and 25 ns bunch spacing

Design of a chopper line for the CERN SPL

The SPL (Superconducting Proton Linac), a 2.2 GeV linac for high-intensity applications under study at CERN, requires a fast chopping at low energy of the H . beam. The most stringent demands on the chopper come from the operation of a Neutrino Factory, which requires 44 MHz bunch frequency in the accumulator ring and in the muon bunch rotation. This imposes a chopper structure with fast rise and fall times, below 2 ns, to remove 3 consecutive 352 MHz bunches out of every 8. An improved design of the standard travelling-wave chopper structure has been analysed and tested on a prototype. Additional effort has gone into the design of a pulse generator or power amplifier capable of providing the required rise and fall times. Since short rise times and high chopper voltages are conflicting requirements, the maximum voltage has been limited to 500 V per plate. A prototype driver has been built and tested. A very compact beam line design is proposed, which is still compatible with the low chopper voltage. The line houses the chopper structure and the dump, provides the separation between chopped and unchopped beam, and matches both from the RFQ and to a DTL. Effects of space charge and of varying beam parameters are analysed. In particular, the influence of the beam energy at the chopper on the line components is discussed in detail. A diagnostic line designed to perform the measurements necessary to validate this set-up is also described

Konjunkturen der NS-Bewegung: eine Untersuchung der Veranstaltungsaktivitäten der Münchener NSDAP, 1925-1930

"Basierend auf den Erkenntnissen der Soziologie sozialer Bewegungen werden die unterschiedlichen Konjunkturen in der Konstitutionsphase der NSDAP in München von 1925 bis 193O untersucht. Insbesondere wird entlang von framing-Strategien der Frage nachgegangen, ob und in welchem Maß die Nutzung besonderer Opportunitätsstrukturen der Partei den Durchbruch bei den Reichstagswahlen im September 1930 ermöglicht hat. Mittels einer inhaltsanalytischen Auswertung der im Völkischen Beobachter angekündigten Vortragsthemen öffentlicher Veranstaltungen der NSDAP in München kann gezeigt werden, daß es der NSDAP in dem ausgeprägten konjunkturellen 'auf und ab' der Parteiaktivitäten seit Anfang 1929 gelungen ist, dank eines zusammenhängenden Rahmens von Themen und deren geschickter Einbindung in identity, injustice und agency frames, spezifische political opportunities in geeigneter Weise in Sinnmuster zu integrieren und als zentrale Probleme für den Bewegungserfolg operativ und effektiv zu nutzen. Diese framing-Leistung ist der NSDAP in ihrer Durchbruchsphase offensichtlich mit eindrucksvollem Erfolg gelungen und hat ihren Aufstieg zur Macht zumindest erleichtert." (Autorenreferat)"Following insights of social movement theory, this paper looks at movement cycles during the initial development of the NSDAP in Munich between 1925 and 1930. The paper explores the different framing strategies the party employed in trying to make efficient use of opportunity structures in the political discourse of the late 1920s, for the mobilizations of resources and popular support. It is argued that changes in framing strategies after 1928 provided an important ingredient leading to the party's political breakthrough with the national elections of September 1930. Based on a content analysis of the official party newspaper, Völkischer Beobachter, the topics of political events and speeches the NSDAP organized in Munich between 1925 and 1930 are analyzed. The results show that, after a period of political difficulties in 1927-1928, the NSDAP managed to achieve a coherent set of themes around economic and political issues that had been characteristically absent in previous periods. Specifically, evidence is found that from 1929 onwards, the party managed to integrate an injustice frame with an identity frame and an agency frame to forge a politically powerful and forward-looking message that may have facilitated both its acceptance among broader segments of the population, and its ultimate rise to power." (author's abstract

Measurement and analysis of SPS kicker magnet heating and outgassing with Different Bunch Spacing

Fast kicker magnets are used to inject beam into and eject beam out of the CERN SPS accelerator ring. These kickers are generally ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. Unless special precautions are taken the impedance of the ferrite yoke can provoke significant beam induced heating, over several hours, even above the Curie temperature of the ferrite. At present the nominal bunch spacing in the SPS is 25 ns, however for an early stage of LHC operation it is preferable to have 50 ns bunch spacing. Machine Development (MD) studies have been carried out with an inter-bunch spacing of 25 ns, 50 ns or 75 ns. For some of the SPS kicker magnets the 75 ns bunch spacing resulted in considerable beam induced heating. In addition the MDs showed that 50 ns bunch spacing could result in a very rapid pressure rise in the kicker magnet and thus cause an interlock. This paper discusses the MD observations of the SPS kickers and analyses the available data to provide explanations for the phenomena: possible remedies are also discussed

Status of Schottky Diagnostics in the ANKA Storage Ring

The status of longitudinal and transverse Schottky observation systems for the synchrotron light source ANKA is presented. ANKA regularly operates in a dedicated low alpha mode with short bunches for the generation of coherent THz radiation. The Schottky measurement results are shown and compared with theoretical predictions for the regular as well as the different stages of the low alpha mode of operation. Special care had to be taken to control and mitigate the impact from strong coherent lines of the short bunches on the signal processing chain. The system setup is shown, expected and unexpected observations as well as applications are discussed

Design Aspects of the RF Contacts for the LHC Beam Vacuum Interconnects

The LHC requires a very low longitudinal and transverse beam coupling impedance, in particular at low frequencies. This implies an admissible DC contact resistance of less than 0.1 m$\Omega$ for the RF contacts inside the vacuum bellows which must carry the image current (up to 50 A peak) of the beam at each vacuum chamber interconnect. Technological aspects, measurement methods and test results are presented for the contacts which will be used in the LHC. The modified mechanical design and the justifications for specific choices will be discusse