Application of the magnetron sputtering technique for the deposition of niobium onto copper RF cavities for particle accelerators – Master Thesis Andrii Tsymbaliuk

Author: Andrii Tsymbaliuk ; Type of thesis: Master Thesis
Abstract: Niobium cavities will be used for super conductive particle accelerators. One of the main challenges is replacing Nb bulk cavities onto Cu cavities, sputtered by the thick Nb layer. In order to improve technology of vacuum sputtering Nb onto copper cavities, the researching work was held.
Many research institutions have studied the sputtering technology applied to complex substrates. The development of the deposition of Niobium onto copper cavities started at CERN from 1980, as a method to replace bulk cavities. Then, at Legnaro National Laboratories (LNL), since 1987 it has been studied the bias diode sputtering in order to deposit Niobium onto copper QWRs for the construction of ALPI accelerator, obtaining positives results: good film uniformity and good performance but lower deposition rates in comparison with other techniques such as magnetron sputtering technique. The magnetron sputtering is a deposition technique widely used in the thin film industry because of advantages of this method.
In the Legnaro National Laboratories were developed three different types of cavities: TESLA-type 9-cell RF cavities, Quarter Wave Resonators, 6 GHz cavities. For each type different magnetron sputtering technique is applied. The aim of the investigation is to analyse the influence of the different magnetron configurations on the Nb sputtering for every type of the developed cavities.

Upgrading of silver edible coatings on cardamom seeds – Master Thesis Vanessa Andreina Garcia Diaz

Author: Vanessa Andreina Garcia Diaz ; Type of thesis: Master Thesis
Abstract: In this work, Cardamom seeds were coated with silver by the Magnetron Sputtering technique. Twenty (20) processes were tested in different ways with wet and dry treatments and then sputtered. The wet treatment was made in order to reduce the size of a sugar buffer coating of the seeds, while surface treatments were applied to improve the aspect of the seeds. The parameters of deposition were 0,2 and 0,15 A of current for the cathode, 5×10-3 mbar pressure of work and the other parameters depend on the samples. The aim of the work was based on obtaining cardamom seeds with a silver coating that has silver appearance and small size. The ideal aspect of the seeds and their sizes are to be similar to the usual Cardamom seeds on the market. For this reason the seeds had a sugar and water layer that avoid degassing from the seeds. A dissolution of this covering was made to reduce their sizes (wet process) and a dry tumbling treatment was applied before deposition process to improve the coating.

Chemical and electrochemical treatments for accelerating cavities – Master Thesis Eduard Chyhyrynets

Author: Eduard Chyhyrynets ; Type of thesis: Master Thesis
Abstract: During my master course I worked mainly in chemical laboratory to proceed chemical and electrochemical treatment protocols that involve several steps, and they vary from Niobium 6 GHz cavities to modeling square copper samples.
My main task was dedicated to the learning different techniques, that were applied to the problem of ARIES project, that makes the second part of this thesis. Here is the list of techniques: electropolishing, chemical polishing, cleaning processes and SEM, EDS, profilometer equipment.
To investigate the role of the substrate in the SRF performances, several surface treatments were applied to a certain amount of copper samples. Here is a list of the treatments involved: chemical polishing, electropolishing, combination of chemical and electrochemical treatment and to mechanical treatment (tumbling). The quality of the sample’s surface were studied and evaluated by visual observation, under SEM, EDS, profilometer and by calculating average removal thickness.
The protocol optimization was done on flat samples in order to study the critical points of the processes and avoid wasting the real samples. In the nearest future, the quality of the work will be evaluated by comparing the performance of Nb thin film on different substrate preparation.

Brazing of Alumina/304 Stainless Steel for rotating joint applications – Master Thesis Davide Carniani

Author: Davide Carniani; Type of thesis: Master Thesis
Abstract: Mechanical face seal is a type of seal widely used in rotating equipment. They apply in all instances where movement is required, from robotics to automotive. Among the many existing fields of application, pumping systems are quite demanding in terms of performance, especially when the device has to be used in harsh environments.
The aim of the project was the development of the process for alumina (Al2O3) and 304 stainless steel in one piece for the realization mechanical systems (mechanical face seals) working in chemically aggressive environments.
Vacuum brazing technique was selected as joining technique to overcome incompatibility in the nature of chemical bonds of the materials involved. Home-made copper-based active brazing alloy (ABA) prepared starting from powders and binder was used to join two materials. A custom oven heated by IR-lamp until 1000°C was used to perform the brazing process.
The objective of the work was to study the process parameters: time of brazing, ramps of heating and cooling, temperature of brazing, issues in the join of chemically and thermo-mechanically different materials, amount of ABA to be applied and types of the binder.
Particular attention was given to the binder, changing the ease of brazing paste application and paste stability during storage, which are important factors for the industrialization of the process.
The process developed was shown to provide good integrity of the samples produced.

Chemical and electrochemical treatments of Copper components for Special applications – Master Thesis Lorenzo Cerasti

Author: Lorenzo Cerasti ; Type of thesis: Master thesis
Abstract: Copper is probably the metal that the human race knows from more time, and in recent
years its use is growing exponentially1. It is employed in every industry, from architecture
to sculpture, from electronics to medicine, from food to musical instruments, and so on.
The ultra-pure Copper then, for its characteristics of thermal and electrical conductivity,
and corrosion resistance (all three exceeded only by Gold and Silver), is critical in special
and advanced applications such as particle physics, the superconducting accelerators
and all the components involved in high value-added applications.
For the latter components, the surface finish is not only an aesthetic whim but a
necessary request.
Roughness plays an important role in determining how a real object will interact with its
environment. Rough surfaces usually wear more quickly and have higher friction
coefficients than smooth surfaces. Roughness is often a good predictor of the
performance of a mechanical component, since irregularities in the surface may form
nucleation sites for cracks or corrosion. Although a high roughness value is often
undesirable, it can be difficult and expensive to control in manufacturing. Decreasing the
roughness of a surface will usually increase its manufacturing costs.
his project work focuses on the ultra high cleaning protocol of Copper components for
particle physics, superconducting cavities and technology transfer of this knowledge to
anodes for X-ray tubes.

Sputtering of Molybdenum thick films for cyclotron targets to produce Technetium-99m – Master Thesis Sara Cisternino

Author: Sara Cisternino ; Type of thesis: Master thesis

99mTc is the principal radioisotope used in medical diagnostics worldwide. Its 6-hour physical half-life and the 140 keV photopeak makes it ideally suited to medical imaging using conventional gamma cameras. 99mTc is derived from its parent element 99Mo that is derived almost exclusively from the fission of uranium-235 targets (using primarily highly-enriched uranium) irradiated in a small number of old-aged research nuclear reactors.
A global shortage of 99Mo exposed vulnerabilities in the supply chain of medical radioisotopes, therefore, individual countries and companies are exploring options for a future supply of medical radioisotopes. Cyclotron-based production of 99mTc starting from 100Mo by 100Mo(p,2n)99mTc reaction has been developed and evaluated at National Institute of Nuclear Physics – Legnaro National Laboratory (LNL-INFN); however some issues must be resolved. Among them innovative target development, because different requirements should be considered:

  • target strength;
  • ability to achieve desired thickness of target material;
  • adherence of target material to baking;
  • chemical resistance of backing;
  • thermal performance at desired current.

Target design strategies, which have been identified in literature, include evaporation, e-beam melting, rolling of thick/self-supported targets, sintering, and electrodeposition. However, they are not performing good enough from the heat conduction point of view. In fact, the resulting targets have high oxidation level and low density, and the deposition technique does not allow to control the thickness and to deposit onto specific substrates .
The purpose of this thesis is the development of an innovative target based on the deposition of the target material, specifically Mo, by magnetron sputtering technique in order to provide high density, thick, uniform and adherent film onto chemically inert backing, as sapphire.
After the sputtering parameter optimization, thick ( ̴ 100 μm) Mo films have been obtained and neither stress nor delamination have been observed.
Successful irradiations were carried out with 16 MeV cyclotron in Sant’Orsola Hospital, in Bologna, with different current beams. In fact, the system has performed at a current of more than 20 μA.

RF Characterization of Thin Film Sputtered Superconducting Resonators – Master Thesis Giovanni Caldarola

Author: Giovanni Caldarola ; Type of thesis: Master Thesis
Abstract: Long time has passed from the discovery of superconductivity, in 1911. Since then theoretical and experimental progress have been made continually. Nevertheless, there are still much to learn about superconductivity and the uses of superconducting materials. At INFN/LNL research and development is being done in order to understand the properties and uses of various superconducting materials to push forward the field of particle accelerator technology. These are used to fabricate radio-frequency (RF) accelerating cavities in order to minimize the power dissipated and increase their figures of merit, such as accelerating gradient (Eacc) and intrinsic quality factor (Q0 or Q) which is a convenient parameter for the number of oscillations it takes the stored energy to dissipate to zero.
Superconducting properties of high purity niobium makes it the preferred material for many accelerator projects using superconducting technology. In fact, niobium possesses very intriguing physical and mechanical properties, not only the highest superconducting transition temperature (Tc) of 9.26°K and the highest superheating field of 240 mT among all available superconducting pure metals but also excellent ductility, which enables machining to be done relatively easily. In addition, the high quality factor and cavity accelerating gradient are fundamental parameters as they affect the overall cost of the accelerator in a direct way.
The accelerating gradient of the superconducting niobium cavities has been remarkably raised in the past decades with an advance of the cavity fabrication technology.
Cavities used to-date are made of niobium either in bulk or niobium coated on copper and are operated at 1.8 and 4.2 °K where the BCS component of the surface resistance is reduced to minimum and the cavity works in the residual resistivity regime.
In Legnaro three laboratories are reserved for cavity treatments and analysis: the chemical, the sputtering and the cryogenic lab, which is dedicated to the whole process of RF testing.
The work will focus on the influence on cavity performance of external surface conditions (in bulk cavity) and of the interface between niobium and copper (in thin film sputtered cavities). Specifically the interest is aimed to investigate how to better allow heat transfer from the resonator to the helium bath

For this purpose, 6 GHz elliptical cavities have been used. The main advantages over a 1.3 or 1.5 GHz superconducting RF cavities (SRF) are saving time, cost and material. Furthermore, due to smaller dimensions, the processes involved have been characterized by a reduction of energy in thermal treatments and a fast cryogenic measurement. A spinning technology is used to create seamless bulk-Nb and bulk-Cu cavities [1].
As a parallel activity, RF characterization of a 101 MHz Nb-Cu QWR (quarter wave resonator) has been conducted and compared with previous tests, varying sputtering parameters.
During the RF test the cavities have to be cooled at cryogenic temperatures in order to reach the superconducting state. In the testing facility there are two apertures which can host a cryostat and allow that this task is accomplished. While 6 GHz elliptical cavities are tested at 4.2°K and then at 1.8°K, for the 101 MHz QWR a temperature of 4.2°K is sufficient.

Protocol for the preparation of alumina/metal brazed joints-Master Thesis MANUEL RAMONES

Author: MANUEL RAMONES ; Type of thesis: Master thesis
Abstract: Brazing is the joining of materials through the use of heat and a filler metal with a melting temperature above 450°C but below the melting point of the metals being joined. This technique joins parts by creating a metallurgical bond between the filler metal and the surfaces of the two materials joined. There are several factors which have direct influence on the final quality of a brazed piece:
the filler metal selection, the heating technique, the atmosphere in which the process is performed, the cleaning procedure, the assembly of pieces, etc. In metal-ceramic junctions, ceramic surfaces, especially oxides, are very stable chemically, consequently, molten metals do not wet them well. There are several techniques that allow to overcome the chemical challenge. In order to develop a procedure that ensures the conditions to achieve a successful brazing process, several techniques for metal-ceramic brazing in a controlled atmosphere (vacuum) were tested. Brazing using active filler metals and direct brazing using ceramic metallization by sputtering were studied in this work. Alumina (Al2O3) was chosen as the ceramic part, whereas stainless steel 304 and Inconel were chosen as metallic components, cylindrical samples were assembled in lap configuration and were heated by IR lamps. The pieces were cut and the cross-section was studied by Scanning Electron Microscope SEM and energy-dispersive X-ray spectroscopy (EDS, EDX) searching for evidence of filler metal uniform spread and diffusion. The samples brazed using Pallabraze 850 disc of 0.01 mm of thickness for braze Inconel and Metallized alumina with 1m of Titanium and using Argon atmosphere showed the more uniform distribution and diffusion.