Category: Thesis

Author: Li Jin Hai ; Type of thesis: Master Thesis
Abstract: The superconductor accelerator cavity is one of the most important and perspective technology for an advance accelerator. For example, the International Committee for Future Accelerators decided that the Linear Collider design had been based on the superconductor technology. Moreover, the accelerator operating with continue wave (CW) mode must use the superconductor technology in stead of the normal conductor technology, such as the Accelerator-driven sub-critical reactor system (ADS), the Accelerator Transmutation of Waste (ATW), the Accelerator Production of Tritium (APT), and so on.
In order to meet all kinds of application, the scientific world interest is now focus on further developments of new resonant cavities fabrication techniques to reduce cost and improve the performance of the accelerator cavity. To realize this object, one of the important methods is to pursue research on new materials. The goal will be the achievement of superconducting cavity working better the Nb ones at 4.2K. For example, the better parameters of the Tc, the surface resistance, the critical field Hc and the Q value are needed.
Up to now, the most possible candidate is Nb3Sn. The Nb3Sn has not only the better superconductivity parameters, but also the stable property and the easy fabrication. There are two methods to fabricate the superconductor cavity with the Nb3Sn, which are including the diffusion method and the multilayer deposition method. In the thesis, we focus on the multilayer deposition method, and …… Continue reading →

Author: Yin Meng ; Type of thesis: Master Thesis
Abstract: Particle physics is now at the threshold of great discoveries. The experiments with particle accelerators and observations of the cosmos have focused attention on phenomena that can not be explained by the standard theory. The technology based on superconducting niobium accelerating cavities can reach a high expenditure of energy by many orders of magnitude lower than that of normal-conducting copper cavities. Even taking into account the power spent to maintain the temperature of liquid helium, the net gain in economic terms is still unassailable.
The sputtering technology was chosen first in the pure diode configuration and subsequently in the magnetron configuration. High Power Impulse Magnetron Sputtering (HIPIMS) is an evolution of the magnetron technique which relies on 100μs high voltage pulses of the order of 1 kV compared to the 300 V of the standard DC magnetron process. During the pulse a huge power density is deposited onto the target, of the order of a few kW/cm2 compared to a few W/cm2 of the standard DC process, producing a highly dense plasma in which also the Nb atoms are partially ionized. These can in turn be attracted to the substrate with a suitable bias. A further advantage of the technique lies in the fact that no hardware changes are required compared to a standard DC biased magnetron system, except for the obvious replacement of the power supply.
In this work, an R&D effort has been undertaken to study the HIPIMS, to improve it and understand the correlation between the parameters applied and the film morphology, the superconducting properties and the RF film quality.
The experiment system is based on the NEW HIGH-RATE SYSTEM for the deposition cavity 1.5 GHz. The experimental details and the measurements of the characteristics of the deposited films are described. Even though the work is still in progress, all of the partial results from now on have been analyzed and commented, in order to extrapolate all the information. The final results are a global overview of the HIPIMS techniques for Nb on 1.5Hz superconducting cavity. Suggestions for future efforts have been included as part of the conclusions. Continue reading →

Author: Rupp Vitalii Volodymyrovych ; Type of thesis: Master Thesis
Abstract: Electropolishing is one of the oldest electrochemical techniques which is widely adapted in industry. Since many years electropolishing has been growing and from day to day it fills more and more niches in different fields of science and technology. Among possible Surface Treatments, electropolishing occupies a key role, because it is the cleanest way for removing hundreds of microns of material. Most galvanic processes start their life from water solutions. Electropolishing is not an exception, even now Nb electropolishing based on water solution with sulfuric and hydrofluoric acids is the most used. Literature results with this standard mixture are excellent,
however the EP of thousands of cavities could become an industrial nightmare from the point of view of security at work. HF is not like other highly corrosive acids: if, by accident, it gets in contact with skin, pain is not felt, but F- ions begin to pass through, searching for the bone calcium.
Since many years world’s science has been interested in ionic liquids and it is not for nothing. A green chemistry based on ionic liquids has come to the fore, and at INFN-LNL laboratories was done the first Niobium electropolishing by a harmless mixture of Choline Chloride and urea heated around 150°C.
In my work I will try to study influence of adding to the mixture some regulators. While it has already been showed the possibility of Nb dissolving with electropolishing effect,I will try to find recipe for technological Nb electropolishing. My second goal is to have ready a
recipe to application on 6 GHz cavities. Continue reading →

Author: Gonzalez, Winder A. ; Type of thesis: Master Thesis
Abstract: 

Vacuum coating processes use a vacuum environment and an atomic or molecular condensable vapor source to deposit thin films, typically less than 5µm in thickness. An example of such a process is magnetron sputtering where material is removed from a solid target by ion bombardment and deposited on a substrate in atomic layers. It is one of the most flexible and controllable methods of generating a metal vapour in vacuum. Applications include low friction coatings for tools, antireflective coatings on glass, semiconductors, decorative coatings e.g. bath taps, touch panel screens, car headlamps, telescope mirrors and coatings for photovoltaics.
A magnetron sputtering source is composed by a cathode, an anode and a combined electric and magnetic field. There are various types of magnetron depending on the application and the target efficiency required. Each type requires an optimized design of magnetic field to ensure operation of the magnetron source. As the price of raw materials becomes higher, the efficiency of the usage of the deposition materials also becomes an important concern.
The purpose of a magnetic field in a sputtering plasma is to increase the efficiency of ionization by capturing electrons emitted from the target to enlarge the rate of the collisions between electrons and neutral gas atoms. The lack of uniformity of the magnetic field produces a non-uniform plasma density, hence differential sputtering rates across the surface of the target. It is obvious that increasing uniformity of the magnetic field will improve the uniformity of the erosion of the target.
This thesis shows the setup of a d.c. magnetron sputtering configuration for a 4″ diameter Copper target, based on a computational study of different magnetic confinements, as well as with an optimization …..
of the erosion sputtered from the target. Continue reading →

Author: Lytovchenko Oleksiyi ; Type of thesis: Master Thesis
Abstract: Photovoltaics constitutes a new form of producing electric energy that is environmentally clean and very modular. In stand-alone installations, it must use storage or another type of generator to provide electricity when the sun is not shining.
Photovoltaics is very suitable as the power supply for remote communication equipment. Its use is increasing rapidly to produce electricity in grid-connected houses and buildings in industrialized countries, despite a 5 to 10 times higher cost than conventional electricity. Crystalline Si technology, both monocrystalline and multicrystalline is today clearly dominant, with about 90% of the market.
Thin-film technology is one of the candidates to take over from Si technology. There are many technological options regarding thin-film materials and methods of deposition but their primary claim to the throne currently occupied by Si is that they can be ultimately produced at much lower cost. Copper oxide is a good candidate for low cost photovoltaic element. It is non toxic and has high absobtion in visible spectra of light. In order to improve it performance doping methods and “partner” component for hetero- or homo –junction have to be studied.
In summary, it is very likely that photovoltaics will become in the next half century an important source of world electricity. Public support and global environmental concerns will keep photovoltaics viable, visible, and vigorous both in new technical developments and user applications. Nations which encourage photovoltaics will be leaders in this shining new technology, leading the way to a cleaner, more equitable twenty-first century, while those that ignore or suppress photovoltaics will be left behind in the green, economic energy revolution. Continue reading →

Author: SERGEY SYNECHKO ; Type of thesis: Master Thesis
Abstract: Continue reading →

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: 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: 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 →