Measurement of the High-Field Q Drop in the TM010 and TE011 Modes in a Niobium Cavity

In the last few years superconducting radio-frequency (rf) cavities made of high-purity ( residual resistivity ratio \u3e 200) niobium achieved accelerating gradients close to the theoretical limits. An obstacle towards achieving reproducibly higher fields is represented by anomalous\u27\u27 losses causing a sharp degradation of the cavity quality factor when the peak surface magnetic field (Bp) is above about 90 mT, in the absence of field emission. This effect, called Q drop\u27\u27 has been measured in many laboratories with single- and multicell cavities mainly in the gigahertz range. In addition, a low-temperature (100 - 140 °C) in situ\u27\u27 baking of the cavity was found to be beneficial in reducing the Q drop. In order to gain some understanding of the nature of these losses, a single- cell cavity has been tested in the TM010 and TE011 modes at 2 K. The feature of the TE011 mode is to have zero electric field on the cavity surface, so that electric field effects can be excluded as a source for the Q drop. This article will present some of the experimental results for different cavity treatments and will compare them with existing models

Observation of Q-degradation in superconducting niobium cavities due to cooldown conditions,

ABSTRACT In the past two years several laboratories around'the world have observed degradations of the Q-value of superconducting niobium cavities made from high purity niobium under certain cool-down conditions. Severe degradations have been reported for larger systems, when they were slowly cooled down or warmed up to temperatures A systematic study of the influence of surface treatments like chemical polishing, anodic oxidation and heat-treatment as well as the cooling conditions on cavity performance of cavities manufactured from niobium of different purity has been conducted. Possible reductions of the Q-degradations by anodic oxidation have been explored. Results of these investigations are reported and changes in material parameters as caused by the degradation are discussed

Analysis of post wet chemistry heat treatment effects on Nb SRF surface resistance

Most of the current research in superconducting radio frequency (SRF) cavities is focused on ways to reduce the construction and operating cost of SRF based accelerators as well as on the development of new or improved cavity processing techniques. The increase in quality factors is the result of the reduction of the surface resistance of the materials. A recent test on a 1.5 GHz single cell cavity made from ingot niobium of medium purity and heat treated at 1400 C in a ultra-high vacuum induction furnace resulted in a residual resistance of about 1nanoohm and a quality factor at 2.0 K increasing with field up to 5x10^10 at a peak magnetic field of 90 mT. In this contribution, we present some results on the investigation of the origin of the extended Q0-increase, obtained by multiple HF rinses, oxypolishing and heat treatment of all Nb cavities.Comment: To be appear in proceeding of SRF 201

Superconducting Cavities from High Thermal Conductivity Niobium for CEBAF

The Continuous Electron Beam Accelerator Facility (CEBAF) is presently under construction in Newport News, VA.The accelerator consists of approximately 169 meters of 5-cell niobium cavities made from high thermal conductivity niobium with RRR values > 250.Cavities have been manufactured of material from three different suppliers.The material properties like thermal conductivity, residual resistivity and tensile behavior are compared.Results on the performance of these cavities in the presence of high rf fields are reported.Q(sub)0 values as high as 10^10 at 2 K and accelerating gradient of E > 14 MV/m have been achieved

Superconducting DC and RF Properties of Ingot Niobium

The thermal conductivity, DC magnetization and penetration depth of large-grain niobium hollow cylindrical rods fabricated from ingots, manufactured by CBMM subjected to chemical and heat treatment were measured. The results confirm the influence of chemical and heat-treatment processes on the superconducting properties, with no significant dependence on the impurity concentrations in the original ingots. Furthermore, RF properties, such as the surface resistance and quench field of the niobium rods were measured using a TE{sub 011} cavity. The hollow niobium rod is the center conductor of this cavity, converting it to a coaxial cavity. The quench field is limited by the critical heat flux through the rods' cooling channel

Nitrogen Doping Study in Ingot Niobium Cavities

Thermal diffusion of nitrogen in superconducting radio frequency cavities at temperatures around 800C has resulted in the increase in quality factor with a low-field Q-rise. However, the maximum accelerating gradients of these doped cavities often reduces below the values achieved by standard treatments. In this contribution, we present the results of the nitrogen diffusion into ingot niobium cavities subjected to successive material removal from the inner cavity surface by electropolishing in an effort to explore the underlying cause for the gradient degradation

Obesity as risk factor for subtypes of breast cancer: results from a prospective cohort study

Background: Earlier epidemiological studies indicate that associations between obesity and breast cancer risk may not only depend on menopausal status and use of exogenous hormones, but might also differ by tumor subtype. Here, we evaluated whether obesity is differentially associated with the risk of breast tumor subtypes, as defined by 6 immunohistochemical markers (ER, PR, HER2, Ki67, Bcl-2 and p53, separately and combined), in the prospective EPIC-Germany Study (n = 27,012). Methods: Formalin-fixed and paraffin-embedded (FFPE) tumor tissues of 657 incident breast cancer cases were used for histopathological analyses. Associations between BMI and breast cancer risk across subtypes were evaluated by multivariable Cox regression models stratified by menopausal status and hormone therapy (HT) use. Results: Among postmenopausal non-users of HT, higher BMI was significantly associated with an increased risk of less aggressive, i.e. ER+, PR+, HER2-, Ki67low, Bcl-2+ and p53- tumors (HR per 5 kg/m2: 1.44 [1.10, 1.90], p = 0.009), but not with risk of more aggressive tumor subtypes. Among postmenopausal users of HT, BMI was significantly inversely associated with less aggressive tumors (HR per 5 kg/m2: 0.68 [0.50, 0.94], p = 0.018). Finally, among pre- and perimenopausal women, Cox regression models did not reveal significant linear associations between BMI and risk of any tumor subtype, although analyses by BMI tertiles showed a significantly lower risk of less aggressive tumors for women in the highest tertile (HR: 0.55 [0.33, 0.93]). Conclusion: Overall, our results suggest that obesity is related to risk of breast tumors with lower aggressiveness, a finding that requires replication in larger-scale analyses of pooled prospective data

Sicherung von Dämmen, Deichen und Stauanlagen : Handbuch für Theorie und Praxis ; Vol. V - 2015

Die Universität Siegen beschäftigt sich seit über 15 Jahren wissenschaftlich und im Bereich der anwendungsorientierten Forschung mit diesem Thema und hat dazu mittlerweile fünf Symposien durchgeführt. Mit der Veröffentlichung soll die langjährige Tradition als etablierte wissenschaftliche Plattform mit einem Wissensaustausch auf europäischer Ebene fortgesetzt werden. Die Bearbeitung dieser Thematik erfolgt auf der Basis der bewährten Kooperation zwischen Geotechnik und Wasserbau an der Universität Siegen. Aktuelle Ereignisse, wie z.B. die aus England oder Australien im Februar des Jahres 2014, machen uns aber auch deutlich, dass ein absoluter Schutz gegen Extremereignisse nicht möglich ist. Sie zeigen aber auch, dass dort wo technischer Hochwasserschutz konsequent umgesetzt wurde Schäden vermieden werden konnten. Wir sind nach den Ereignissen in den vergangenen Jahren aufgefordert wissenschaftlich noch leistungsfähigere und duktilere Systeme zu entwickeln. Weiter ist die Wissenschaft in der Pflicht, die Zivile Sicherheit im Hochwasser-schutz permanent zu bewerten, zu bearbeiten und ganzheitliche-interdisziplinäre und länderübergreifende Lösungen für die Zivilgesellschaft einzufordern

Contamination issues in superconducting cavity technology

The application of radio-frequency superconductivity technology in particle accelerator projects has become increasingly evident in recent years. Several large scale projects around the world are either completed or close to completion, such as CEBAF, HERA, TRISTAN and LEP. And superconducting cavity technology is seriously being considered for future applications in linear colliders (TESLA), high current proton accelerators (APT, spallation neutron sources), muon colliders and free electron lasers for industrial application. The reason for this multitude of activities are matured technology based on a better understanding of the phenomena encountered in superconducting cavities and the influence of improved material properties and contamination and quality control measures