Category: Master Thesis

Author: Lanza Giulia ; Type of thesis: Master Thesis
Abstract: In Legnaro three laboratories are reserved for cavity treatments and analysis:the chemical lab, the sputtering lab and the cryogenic lab.
The chemical lab has the facilities for the surface treatment of single cell cavities as well as TESLA 3-cell structures. It is possible to treat two cavities (one of copper and one of niobium) at the same time. In fact, under the extractor fan, there are two completed circuits, one dedicated to the electropolishing and the chemical polishing of niobium cavities and the other one for copper cavities.
At the superconductivity lab in Legnaro it’s possible to measure a 1,5 GHz mono-cell cavity in four days: High Pressure Water Rinsing, pump down, cooling, measure at 4,2K and measure at 1,8K. During the rf test, the cavity has to be cooled at cryogenic temperatures in order to reach the superconducting state. In the rf testing facility there are four
apertures which can host a cryostat. Three of them are used to test QWRs and single cell TESLA type cavity. This kind of cryostat can hold 100 liters of helium. The last one is for the multi-cells TESLA type cavity with a volume of 400 liters of helium. This cryostat has been designed for operating at 4.2K and 1.8K with a maximum power of 70
W. In order to reduce the cooling cost, a preliminary cooling is achieved by using the liquid nitrogen of the second chamber. Once the temperature reaches 80Kthe transfer of liquid He at 4.2K into the main vessel is started.Then the temperature of liquid helium can be lowered decreasing the chamber pressure. The cavity is tested at 4.2K and then at 1.8K, it is mounted on a vertical stand and it is connected to a pumping line. Remote systems monitor its temperature, its pressure and the transmission of the radiofrequency.
All the procedures for cavity preparation need qualified and expert operators that know every sequence of operations. This report is the starting point to train new peoples and the reference point for the staff working on NbCu cavities. Continue reading →

Author: KAABI Walid ; Type of thesis: Master Thesis
Abstract: LAL-Orsay is developing an important effort on R&D and technology studies on RF power couplers for superconductive cavities. These are complex and high technology devices due to their basic functions: RF power matching between source and cavity, vacuum and temperature separation from the environment to the cavity. One of the most critical components of high power couplers is the RF ceramic window that allows the power flux to be injected in the coaxial line. The presence of a dielectric window on an RF power line has in fact a strong influence on the multipactor phenomena, a resonant electron discharge that is strongly limiting for the RF components performances. Due to its low secondary electron emission coefficient, TiN thin film is used as a multipactor suppressor coating on ceramic coupler windows. In addition, TiN permits to drain away electric charges on the surfaces to avoid material break down.
In this framework, a sputtering machine was developed allowing thin layer titanium nitride coating on ceramic. The coupler operating conditions, the physical properties of TiN layer and alumina substrate in addition to windows geometries have defined the strict constraints that have been taken into account in the definition of the coating bench design. By maintaining a constant bias and a fixed ionisation gas flow, an optimisation of reactive gas flow will be necessary for stoichiometric deposit obtaining. Once these parameters determined, a study of deposition rate variation for different process pressure value will be done. As TiN deposit thickness is a very important parameter to control, a correlation between quartz crystal microbalance given value and the real deposition thickness is determined for a better in-situ monitoring. Continue reading →

Author: Deambrosis Silvia ; Type of thesis: Master Thesis
Abstract: Preparation of cavity walls has been one of the major problems in superconducting radio-frequency (SRF) accelerator technology. Accelerator performance depends directly on the physical and chemical characteristics at the SRF cavity surface. The ambitious objective of this project is to study a cavity surface preparation process which is superior in terms of cost, performance, and safety, to the wet chemical process currently in use. Plasma based processes provide an excellent opportunity to achieve these goals. Plasmas are chemically active media. Depending on the way they are activated and their working power, they can generate low or very high “temperatures” and are referred correspondingly as cold or thermal plasmas. This wide temperature range enables various applications for plasma technologies: surface coatings, waste destruction, gas treatments, chemical synthesis, machining … many of these techniques have been industrialized. A large number of important industrial plasma applications are carried out close to atmospheric pressure, in many cases in atmospheric air. The fascinating possibility to perform cleaning and/or etching processes of RF cavities without the need of any vacuum pumping system has to be deeply explored realizing different atmospheric con gurations as corona plasma, rf resonance plasma, plasma jet and torch. Thermal plasmas (especially arc plasma) were extensively industrialized, principally by aeronautic sector. Cold plasma technologies have been developed in the microelectronics but their vacuum equipment limits their implantation. To avoid drawback associated with vacuum, several laboratories have tried to transpose to atmospheric pressure processes that work under vacuum for the moment. Their researches have led to various original sources. In the textile sector, a number of plasma applications are conceivable and some have been tested in laboratory scale. The chemical functionality and/or the morphology of a ber surface can be altered in order to improve very di erent properties to tailor them for certain demands. The wettability can be increased to achieve a better impregnation or a deeper dying or, in contrast; it also can be decreased to create a water repellent behavior. New chemical functionalities on the surface can promote the reactivity with dyes. The water free removal of sizings seems to be possible. These are only a few examples that demonstrate the potential of this technology. We decided to try to ignite a resonance atmospheric plasma into 1.5 GHz superconducting niobium cavities to perform a feasibility study. The second step has been the attempt to understand what really happens to the resonant structure internal surface. The most powerful tool consists in the atmospheric plasma treatment and fast rf characterization of 6 GHz small resonators. Continue reading →

Author: Rossi Antonio Alessandro ; Type of thesis: Master Thesis
Abstract: Since the International Committee for Future Accelerators recommended that the Linear Collider design has to be based on the superconducting technology, the scientific world interest is now focused on further developments of new resonant cavities fabrication techniques and cost reduction.
It is important to pursue research on new materials: the goal will be the achievement of superconducting cavities working better than the Nb ones at 4.2 K.
However the high beta 1.5 GHz resonant structure research, especially in this time of international economic recession, would become prohibitive and onerous both for the material costs, of production and treatments, and the cryogenic expense.
For this reason it is mandatory for the future of superconducting resonant cavities to cut down the costs introducing a new research concept. The idea is to build micro cavities 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. But, a common limitation of systems used for this, often consists in the difficulty 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.
We will proof that a mini low cost laboratory could be set up to study our 6 GHz samples in all the aspects of interest. The mentioned mini-lab consists in:
* A reduced size mechanical polishing bench
* A chemical/electrochemical minilab for BCP EP
* A mini oven for thermal treatments
* A miniaturized sputtering system
* An inexpensive cryogenics and quick RF measurements Continue reading →

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 →