Clearance flow-generated transverse forces at the rotors of thermal turbomachines

Self-excited rotor whirl represents a serious hazard in the operation of turbomachines. The reported investigation has, therefore, the objective to measure the lateral forces acting on the rotor and to determine the characteristic pressure distribution in the rotor clearance area. A description is presented of an approach for calculating the leakage flow in the case of an eccentric rotor position on the basis of empirical loss coefficients. The results are reported of an experimental investigation with a turbine stage, taking into account a variation of the clearance characteristics. The pressure data measured are consistent with the theoretical considerations

Revised Phase Diagram of the Gross-Neveu Model

We confirm earlier hints that the conventional phase diagram of the discrete chiral Gross-Neveu model in the large N limit is deficient at non-zero chemical potential. We present the corrected phase diagram constructed in mean field theory. It has three different phases, including a kink-antikink crystal phase. All transitions are second order. The driving mechanism for the new structure of baryonic matter in the Gross-Neveu model is an Overhauser type instability with gap formation at the Fermi surface.Comment: Revtex, 12 pages, 15 figures; v2: Axis labelling in Fig. 9 correcte

Werkstoffe fuer fortschrittliche Komponenten in Kraftwerken mit hohem Wirkungsgrad und niedriger Emission. Qualifizierung von zwei Mischschweissverbindungen am Werkstoff G-X12 CrMoWVNb 10 11

The efficiency of power plants can be improved by increasing the steam temperature. Cost-efficient design improvements are achieved by using welded turbine casings made from materials modified according to service steam temperatures in the various applications. The main advantages achieved are better exploitation of the higher creep strength, and enhanced weldability of the new cast steel material. The tests performed so far in high-efficiency steam turbines resulted in development of combinations of the new cast steel material G-X12 CrMoWV NbN 10 11 with conventional, low-alloyed materials. Problems arising with these combinations are linked to finding a standard annealing temperature suitable for all materials. Two dissimilar welds with conventional, low-alloyed materials were to be qualified. The welding quality of the two test welds is good. The mechanical strength data achieved at room temperature and elevated temperatures are sufficient and are higher than the minimum strength data required for the low-alloyed materials. The weakest point of the weld made at room temperature is the low-alloy HAZ in the decarburized region, but this effect disappears at elevated temperatures (500 and 550 C). (orig./MM)Der Wirkungsgrad von Karaftwerken kann durch die Erhoehung der Dampftemperatur verbessert werden. Kostenguenstige Konstruktionsloesungen werden durch geschweisste Turbinengehaeuse unter Verwendung von Werkstoffen erreicht, die in den unterschiedlichen Bereichen den aktuellen Dampftemperaturen angepasst sind. Hauptvorteil der neuen Anwendung ist die Ausnutzung der hoeheren Kriechfestigkeit wie auch der besseren Schweissbarkeit des neuen Stahlguss-Werkstoffes. Dies fuehrt erstmalig bei Hochleistungs-Dampfturbinen zu Kombinationen der neuen Stahlgussqualitaet G-X12 CrMoWV NbN 10 11 mit konventionellen niedriglegierten Staehlen fuer hoehere Temperaturen. Bei diesen Werkstoffkombinationen ergeben sich Probleme hinsichtlich einer einheitlichen Spannungsarmgluehtemperatur. Es sind zwei Mischschweissverbindungen mit konventionellem niedriglegierten Materialien zu qualifizieren. Die Schweissnahtqualitaet beider Testschweissungen ist gut. Die erreichten mechanischen Werte bei Raumtemperatur und erhoehten Temperaturen sind ausreichend und liegen ueber den Mindestwerten der niedriglegierten Werkstoffe. Der schwaechste Teil der Verbindung bei Raumtemperatur liegt in der niedriglegierten Waermeeinflusszone im entkohlten Bereich, allerdings verschwindet dieser Effekt bei hoeheren Temperaturen (500 und 550 C). (orig./MM)Available from TIB Hannover: F97B1520 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Pulsed electron lenses for space charge compensation in the FAIR synchrotrons

The FAIR heavy-ion synchrotrons SIS18 and SIS100 as part of the new FAIR accelerator facility at GSI will be operated at the "space charge limit" for light and heavy-ion beams. In SIS100 beam loss due to space charge induced resonance crossing should not exceed a few percent during the 1 s injection plateau. In order to further increase the beam intensities beyond the FAIR reference parameters, a new concept of (partial) space charge compensation by pulsed electron lenses is considered. We describe the general space charge compensation concept together with detailed simulations results. A prototype lens for SIS18 is presently under development and will be used to validate the concept. This new approach, aiming for mitigating the most prominent intensity limitation, should be applicable to many of the existing large scale proton and heavy-ion synchrotrons world wide

Pulsed electron lenses for space charge compensation in the FAIR synchrotrons

The FAIR heavy-ion synchrotrons SIS18 and SIS100 as part of the new FAIR accelerator facility at GSI will be operated at the "space charge limit" for light and heavy-ion beams. In SIS100 beam loss due to space charge induced resonance crossing should not exceed a few percent during the 1 s injection plateau. In order to further increase the beam intensities beyond the FAIR reference parameters, a new concept of (partial) space charge compensation by pulsed electron lenses is considered. We describe the general space charge compensation concept together with detailed simulations results. A prototype lens for SIS18 is presently under development and will be used to validate the concept. This new approach, aiming for mitigating the most prominent intensity limitation, should be applicable to many of the existing large scale proton and heavy-ion synchrotrons world wide

Status of the development of the electron lens for space charge compensation at GSI

At GSI a prototype electron lens for space charge (SC) compensation is currently being designed and main components as the RF-modulated electron gun are already under commissioning. The goal of this project is the (partial) compensation of SC forces within the ion beam by an overlapping electron beam. This may help to increase the intensity of primary beams, especially in the FAIR facility and potentially all large synchrotrons operated at the SC limit. For an effective SC compensation, the generated electron beam needs to follow the transverse and longitudinal beam profile of the ion bunch structure. The requirements are maximum currents of 10 A and grid modulation to cover a broad frequency range from 400 kHz to 1 MHz. The RF-modulated electron gun was designed and manufactured in the scope of the ARIES collaboration and is currently being tested at the E-Lens Lab of Goethe-University Frankfurt. A dedicated test bench was built for commissioning of the major e-lens components and diagnostics. In this contribution the overall set-up will be presented putting special emphasis on the beam dynamics and collector design as well as simulation results of the electron gun