Author: SILVIA MARIA DEAMBROSIS ; Type of thesis: PhD Thesis
Abstract: For superconducting alloys and compounds, at a given operating temperature, the best rf performances (low surface resistance and high relevant critical fi elds) are obtained for high Tc and low resistivity materials. Among the possible candidates, A15 compounds appear to be the most promising.
We needed a fast, easy and performing way to characterize A15 superconducting materials for their potential application to accelerating resonators. The idea is to build microcavities completely equal in shape to the real scale model. The rf characterization of samples is an useful diagnostic tool to accurately investigate local properties of superconducting materials. However, a common limitation of systems used for this, often consists in the di culty of scaling the measured results to the real resonator.
In this work we will proof that 6 GHz resonators can simply become our cavity shaped samples. Our attention was focused on two materials: V3Si that has a really high RRR value and Nb3Sn that is the only A15 material already used for a resonant accelerating structure.
The process parameters optimization necessary to improve the A15 phase superconducting properties, crystal structure and morphology is going on through the small sample production: this is fundamental but still not enough. Continue reading
Category: Thesis
NEW MAGNETRON CONFIGURATIONS FOR SPUTTERING NIOBIUM THIN FILMS INTO COPPER TESLA-TYPE SUPERCONDUCTING CAVITIES-PhD Thesis Lanza Giulia
Author: Lanza Giulia ; Type of thesis: PhD Thesis
Abstract: Superconducting radiofrequency resonators for particle acceleration have become a standard component for particle accelerators. This work described an in-depth study and development of an alternative to the more frequently used bulk niobium cavities: niobium thin film coated into a copper cavity. The first niobium-coated copper cavity was produced at CERN in the early eighties. The sputter technology was chosen first in the pure diode configuration and subsequently in the magnetron configuration. The latter was adopted for the successful series production of the LEP and LHC cavities. In this work an intensive R&D effort has been undertaken to study the coating technique, to improve it and understand the correlation between the coating system applied and the film morphology, the superconducting properties and the RF film quality. Four different coating configurations for sputtering niobium films into 1.5 GHz copper cavities has been explored. First, the standard technique applied for several years at CERN to coat the LEP cavities has been reproduced. Then, in order to improve the Nb film quality,the application of three main ideas to the sputtering process was investigated: i) making niobium atoms imping perpendicularly to the substrate surface, ii) promoting the effect of plasma bombardment on the growing film, iii) increasing the sputtering rate. Therefore, three different and new sputtering configurations are described: the effect of Nb atoms arriving perpendicularly to the substrate was explored either by using a cathode that follows the cavity shape (Large Area Cavity Shaped Cathode) or by increasing the plasma confinement efficiency by means of a target parallel to the magnetic field lines (Ringed Shaped
Cathode). The removal of adsorbed impurities from the film surface and the increase of the film density were investigated by using a biased third electrode that promoted the positive ion bombardment of the growing film. A mixed Bias-Magnetron system was built using a positively charged metal grid which surrounded the cathode. Different film characteristics were studied and compared, focusing mainly on superconducting and resistive properties. Also morphological and microstructural properties were analyzed in a very valuable collaboration with “Interdepartmental Laboratory of Electron Microscopy” (LIME), University of Rome “Roma Tre”, at the Mechanical and Industrial Engineering Department. Four RF test on different accelerating cavities are reported and commented. In addition a 3-cell bulk niobium 1.3 GHz cavity were prepared and measured in order to compare bulk and thin film results. Even though the work is still in progress all of the partial results to-date have been viii Abstract analyzed and commented, in order to extrapolate every possible information. The final result is a global overview of the sputtering coating techniques and a of the results obtained using each system. Suggestions for future efforts have been included as part of the conclusions. Continue reading
DEVELOPMENT AND CHARACTERIZATION OF A PLASMA-NEEDLE FOR BIOMEDICAL APPLICATIONS-Foreign Institute Thesis Matthias Bäcker
Author: Matthias Bäcker ; Type of thesis: Foreign Institute Thesis
Abstract:
Due to their unique properties, plasmas have found a broad range of applications in biotechnology and biomedicine, including surface modification of implants and instruments by plasma activation or the deposition of specific diamond-like- and biocompatible structures. A completely new field is the investigation of plasma interaction with biological tissues and the exploration of potential applications.
In contrast to low pressure plasmas, atmospheric pressure plasmas can be operated more conveniently at ambient air and do not require costly vacuum systems. However, the physical properties of a plasma alter significantly with increasing pressure. Therefore, there is a steadily increasing interest in plasma-needles in recent years. These plasma- needles operate stably at atmospheric pressure without producing (filamentary) arcs, but are restricted to their size. Arcs can develop temperatures of several thousand degrees Kelvin and are therefore undesired. The construction of plasma-needle arrays can compensate the reduced effectiveness of a single plasma-needle. The low temperature of the back- ground gas and comparable high electron density of such plasma-needles offer manifold applications.
The objective of this work is the setup of a new atmospheric plasma device for the exploration of its diverse applications with focus on biomedical applications. With the help of comparable work and on the basis of preliminary experiments, a new plasma-needle has been fabricated. Subsequent, that plasma-needle was initially characterized and experimentally tested for thin film deposition and surface modification and is ready for tests on bacteria inactivation.
At first, a review of the state-of-the-art and current research on plasma-needles and their biomedical applications is given. The following two chapters deal with the basics of plasma physics, the experimental setup and the diagnostic tools as well as the principle of the plasma-needle. The results of the different measurements are presented and discussed in chapter five.
The following diagram is intended to help understanding the different steps of the work progress. After an introductory literature review, preliminary experiments with different plasma sources were executed. Thereupon, a prototype was constructed, which then was characterized and tested on two different possible applications, surface activation and carbon film deposition.
Application of the Magnetron Sputtering Technique to the development of a Contrast Detail Test Object for mammography-Master Thesis BERMUDEZ JUDILKA
Author: BERMUDEZ JUDILKA ; Type of thesis: Master Thesis
Abstract: In the past few decades a large amount of attention has been given to health service’s technology. Advances in electronic components, computer technology, and images processing have contributed considerably to the expansion and improvement of the field. However, there is evidence that several other related topics still need to be explored, such as X-ray imaging in the routine mass screening for medical diagnosis.
Tumors formation is one of the most common human health problems and large efforts have been undertaken world wide to tackle the disease. Breast cancer specifically seems to affect a large percentage of the female population. Research indicates that breast cancer treatment is most effective if the disease is diagnosed in its early stages of development. Traditionally, X-ray technologies have been used for breast screening film mammography and its success in detecting breast cancer has been reconfirmed throughout the past few decades. However, the technique has several limitations, and further improvements are required if we wish to achieve early stage diagnosis. Image formation in radiological diagnosis is the result of the complex interdependence of many factor. Creating an ideal balance among them could improve the image to such a degree that it could be used in a clinical setting, where the minimum radiation dose would be applied to the patient. The factors which increase radiation dose and affect image quality can be grouped as: radiation quality, photon intensity, Xray detection sensitivity, and reduction of background through scattered radiation. Optimum performance is dependent on the improvement of the assessments of these phenomena. In the past, standard methods of quality control have been introduced which have lead to a partial improvement in the image evaluation techniques. Some methods, widely applied, involve the use of test objects or phantoms for the establishment of comparison parameters. However, the methods that use phantoms, are frequently not
as reliable as radiation based diagnoses of asymptomatic woman produce. In addition,the subjective nature of image interpretation by medical professionals can make the assessment process very difficult. Consequently, the currently available tools which are used for breast clinical image formation and interpretation regularly results in an incorrect diagnosis.
In past years, the commercially introduced digital detectors for mammography were seen as an important advancement since they provided both a higher acquisition speed and a lower associated radiation dose. However, up until this point, the quality of the produced images is comparable to the images obtained with film detectors. Even though applying a lower dose represents a great advantage, there is no improvement in image quality production. In addition, has been demonstrated that using traditional phantoms, to evaluate image quality on digital mammography, did not bring enough information about certainties on dose measurements. But a new window is open for innovation, since dose control on digital mammography systems depends on factors where major improvement can be achieved. Theoretically, it is possible to enhance discriminating threshold and therefore improve image interpretation at a higher degree. Although at the moment it has still not been achieved, it is within reach since there is currently underway the development of new instruments which have a better approach for the assessment of digital mammography systems. We propose one of the improvements.
The construction and research of the uniformity and replicability of a contrast detail test object could represent an advance in this research field. Until now, a phantom use for digital mammography has not been provided, that can provide both uniformity and reproducibility such that it could be used as a main interpretational tool. This knowledge would allow for the establishment of standard parameters in both the systematic and even auto Continue reading
FEASIBILITY STUDY OF A SPUTTERED RADIOFREQUENCY QUADRUPOLE-Foreign Institute Thesis Anila Gottschling
Author: Anila Gottschling ; Type of thesis: Foreign Institute Thesis
Abstract: Superconducting technology is becoming the standard route for supplying power to high-energy particle beams. Radiofrequency (RF) electric fields provide the motive power for high-energy accelerators. Superconducting Radio Frequency structures which are used for acceleration of low velocity ions are successfully operating in HERA at DESY (Germany), LEP at CERN (Switzerland) TRISTAN at KEK (Japan). A superconducting booster has the advantage that preserves the good quality of tandem beams and at the same time operating in CW (continuous work) mode has the capability to accept a high percentage of injected tandem current. The BCS surface resistance decreases rapidly at resonators of low frequencies and this permits operating at a temperature of 4,2 K (i.e. avoiding the use of expensive superfluid helium). The low b accelerating structures have been under development in the last two decades and this is related to their employment in energy boosters for …. please download the pdf file Continue reading
ELABORATION ET CARACTERISATION DE FILMS DE NIOBIUM DEPOISES SUR CUIVRE DETERMINATION DE LA RESISTANCE DE SURFACE DE SUPRACONDUCTEURS PAR THERMOMETRIE SOUS VIDE-Foreign Institute Thesis MARION RIBEDEAU
Author: MARION RIBEDEAU ; Type of thesis: Foreign Institute Thesis
Abstract: Continue reading
Herstellung von Supraleitenden Duennen V3Si Filmen Durch DC Magnetron Sputtering-Foreign Institute Thesis Klaus Schirmer
Author: Klaus Schirmer ; Type of thesis: Foreign Institute Thesis
Abstract: The TESLA linear Collider would rely on superconducting structures at 1,3 GHz with a gradient of 25 MV/m and an unloaded quality factor at temperatures of 2 K. However Nb Technology asks for superfluid e cooling systems. The use of a higher critical temperature superconductors would allow to adopt the simpler 4,2 K cryogenics. V3Si has a reported Tc value of 17 K and RRR values up to 80 …. it follows –> Continue reading
Herstellung von Supraleitenden Duennen V3Si Filmen Durch DC Magnetron Sputtering – Klaus Schirmer
Data: 10/01/1998
Abstract: The TESLA linear Collider would rely on superconducting structures at 1,3 GHz with a gradient of 25 MV/m and an unloaded quality factor at temperatures of 2 K.
However Nb Technology asks for superfluid e cooling systems. The use of a higher critical temperature superconductors would allow to adopt the simpler 4,2 K cryogenics.
V3Si has a reported Tc value of 17 K and RRR values up to 80 …. it follows –>
Author: Klaus Schirmer
Sputtering niobium films into a RFQ model & Sputtering of superconducting V3Si film-Foreign Institute Thesis ZHANG YAN
Author: ZHANG YAN ; Type of thesis: Foreign Institute Thesis
Abstract: Superconducting technique has been widely applied to linac particle accelerators for more than two decades. Cryogenic RF performance of SC cavities has been improved a lot due to improvement on purification of SC material, as well as SC cavity design, fabrication and surface treatment techniques. The Sputtering technique of SC cavities provided another chance to particle accelerators: the cost of cavity fabrication greatly decreased, while the performances of sputtering coated niobium cavities are competitive with those of bulk material SC cavities.
In this thesis some important features of RF cavities are briefly introduced; the difference in design of a SC cavity and that of a normal conducting cavity are indicated. The design parameters of a 144 MHz SC QWR and an 1.5GHz monocell spherical cavity are presented. The SC material for cavity fabrication, and measurement method of SC cavity are introduced, then the fabrication and surface treatment technique of SC cavities are discussed.
The application of sputtering technique in SC cavities is a recent development of SRF technique. After nearly two decades study, the sputtering coated niobium film SC cavities achieved a cryogenic RF performance close to that of bulk niobium cavities. The thesis introduced various sputtering techniques on this purpose from preliminary glow discharge, discusses the LNL, Peking University and Australia National University’s QWR sputtering configurations, and introduces LNL’s surface treatment technique for copper substrate cavity.
In the study of niobium sputtering for 1.5GHz monocell spherical cavity, different magnetron configurations were tried and measured a large amount of sputtered niobium samples. By improving the magnetron configuration and surface treatment technique of the substrate cavity, sputtered niobium cavities with better RF performance were obtained. It was found out that substrate surface treatment takes a very important role in the sputtering of a SC cavity, as sample measurement cannot give out helpful information of the RF performance, the study with substrate Continue reading
Sputtern von Supraleitundem Duennen Filmen fuer Radiofrequenz Beschleuigungsresonatoren-Foreign Institute Thesis JUERGEN BRODERS
Author: JUERGEN BRODERS ; Type of thesis: Foreign Institute Thesis
Abstract: A cylindrical postmagnetron has been designed for sputtering Niobium films into 1,5 Ghz monocell Copper cavities of the TESLA-type.
For sputtering 1.5 GHz monocells we built a cylindrical post-magnetron . The idea under such a design was the search of high sputtering rates and high thickness uniformity of the coating sampled along the cavity profile. Higher sputtering rates respect to classical cylindrical magnetron are possible when sputtering from the whole target surface. The advantage is twofold: the fraction of impurities trapped in the film linearly decreases versus deposition rate, moreover the deposition takes shorter time.
On the other side for the classical cylindrical magnetron, when the discharge is switch on, plasma do not live simultaneously on the whole target surface, instead it is strictly confined onto the target surface portion where ionizing electrons are trapped by magnetic field lines. A large portion of target surface, the one just outside of the magnetic trap, reaches high temperatures as well, but there is not sputtering from it, unless the electromagnet is moved toward this region.
On the basis of our experience on cylindrical magnetrons of such a design, we have observed that films untouched by plasma have systematically worse purity than films immersed in the discharge. This problem becomes not important for postmagnetrons,since the whole target surface is sputtered simultaneously. When designing a post-magnetron two choiceswere possible: a) the cathode must follow the profile of the cavity, keeping the magnetic field lines constantly parallel to the target. End losses being avoided by an electrostatic mirror outside of the cavity. In this case the shape of the target is rather complicated since to get into the narrow bore of the cutoff,it must be collapsible. b) the cathode is a straight tube and
the magnetic field follows the shape of the cavity. Continue reading