Author: Cristian Pira; Type of thesis: PhD Thesis
Abstract: A key challenge for the next accelerators is the cost reduction. Bulk niobium cavities performances are closer to their theoretical limits and an alternative technology is mandatory. Niobium thin film copper cavities are the most explored solution, but the Q-slope characteristic of these resonators limits the applications where high accelerating fields are requested. In this work an original approach is adopted in order to enhance the performances of sputtered cavities, exploring the possibility to sputter 70 micron thick films to straighten up the Q-slope in Niobium sputtered copper cavities. The engineering of Nb thick films deposition on 6 GHz copper cavities, necessary to minimize the stress on niobium thick films and avoid film peeling from the substrate, is reported. Thick films show RRR values over 60. Different strategies have been used for stress reduction: deposition at high temperature of 550 °C, deposition at the zero stress pressure point (5∙10-2 mbar), and the development of a multilayer deposition procedure. Rf tests at 4,2 K and 1,8 K on 6 GHz resonant cavities are the tool used to evaluate the influence of the critical deposition parameters on the cavity performances. Two different venting procedures have been tested: a standard one, and a high temperature one, in which pure nitrogen is inserted in the vacuum chamber immediately after the end of the sputtering process. Thick films open the possibility to post treatments on sputtered cavities: the effect of buffer chemical polishing and heat treatments at different temperature have been investigated. The Rf tests on 6 GHz cavities show the fundamental role played by the surface preparation and the possibility to enhance the maximum accelerating field minimizing the film stress. Above all, for the first time, the possibility to obtain flat curve of Q-factor versus accelerating field in sputtered cavities with thick films it is demonstrated.
Category: Thesis
Development of novel cyclotron target for 99mTc production – Hanna Skliarova PhD Thesis
Author: Hanna Skliarova; Type of thesis: PhD Thesis
Abstract: Il 99mTc è un radionuclide estremamente importante, utilizzato in più dell’80% degli esami diagnostici. Generalmente, il 99mTc viene estratto da generatori portatili contenenti il 99Mo (quest’ultimo proveniente dai reattori a fissione che utilizzano 235U altamente arricchito). Il 95% di tutta la produzione mondiale del radionuclide 99Mo è attualmente supportato da cinque impianti nucleari, alcuni dei quali hanno raggiunto più di 50 anni di attività. E sono pertanto esposti a frequenti e improvvise interruzioni che causano periodici cali nella produzione del 99Mo. Presso i Laboratori Nazionali di Legnaro dell’Istituto Nazionale di Fisica Nucleare (LNL-INFN) si è scelta la strategia basata su acceleratore, come alternativa alla via standard per avere una soluzione di riserva in caso di una nuova crisi del 99mTc. Tra le varie possibilità studiate, la migliore, e più promettente, è la produzione diretta del 99mTc attraverso l’irraggiamento, con fascio di protoni, di target di 100Mo arricchito. Un’ulteriore alternativa è la produzione nel nuclide precursore 99Mo nella stessa cornice di irraggiamento. Riguardo la produzione indiretta del 99Mo, il principale svantaggio è l’attività specifica piuttosto bassa se paragonata alla fissione nucleare nei reattori. Pertanto, la produzione del 99mTc a partire dalla reazione 100Mo(p,2n)99mTc, è stata sviluppata e valutata presso LNL-INFN; tuttavia alcune questioni devono ancora essere risolte. Il problema chiave in esame è il design e la costruzione di un target idoneo per la produzione del radionuclide e il recupero del costoso isotopo 100Mo dopo la produzione del radiofarmaco a base di 99mTc. Infatti, solo una tecnologia consolidata e a circuito chiuso può rendere competitiva la via basata sull’acceleratore con la produzione standard basata sul reattore nucleare. Per massimizzare la resa della reazione nucleare, la produzione dovrebbe essere effettuata alle massime correnti protoniche. Questo significa che il target dovrebbe fornire un’elevata efficienza di dissipazione del calore. Un sistema di target solido standard si suppone essere costituito dal materiale target depositato su un backing plate, raffreddato con liquidi. Per massimizzare la dissipazione del calore, il target dovrebbe essere costruito con un materiale avente la massima conducibilità termica, e dovrebbe essere usato un metodo che fornisca un buon contatto termo-meccanico tra il materiale target in sé e il backing plate. Al fine di consentire la massima velocità di produzione di 99mTc attraverso il ciclotrone, la tecnica di deposizione metallica deve garantire: • buona conducibilità termica del Mo; • spessore uniforme e controllato dello strato di Mo; • elevata densità del Mo (bulk-like); • basso livello di ossidazione del Mo; • buon contatto termo-meccanico con il backing plate. Le più comuni tecniche di deposizione per produrre il target di Mo, che includono la sinterizzazione, l’elettrodeposizione, laser melting, laminazione, ecc., non sono in grado di soddisfare i suddetti requisiti. Il gruppo dell’LNL-INFN ha proposto di usare il magnetron sputtering come tecnica base per depositare il 100Mo direttamente su un backing plate. Una delle principali sfide tecnologiche di questa tesi è stata quella di sviluppare un metodo per depositare film ultra spessi (centinaia di micrometri) di metalli refrattari (Nb e Mo) con la tecnica magnetron sputtering. I film depositati con il metodo proposto sono risultati densi (>98% della densità bulk) e aderenti al backing plate ad alta conducibilità termica. Il comportamento termico del sistema (100 µm di spessore di Mo depositato su un backing di rame) è stato testato sotto fascio a 15.6 MeV e 60 µA. Il film di Mo spesso 100 µm depositato con la tecnica magnetron sputtering sul backing di rame ha mostrato un’eccellente stabilità termomeccanica (nessuna delaminazione o rottura) sotto un fascio di protoni di circa 1 kW/cm2 di densità di potenza. Il rame è lontano dall’essere un materiale ideale per il backing plate, poiché si dissolve nella soluzione reattiva di H2O2 nella quale il materiale target è normalmente disciolto dopo l’irraggiamento e prima della separazione chimica, utilizzando un modulo 100Mo/99mTc. Questi svantaggi costringono ad usare moduli di separazione aggiuntivi per ottenere il prodotto finale puro, ma questi sono incompatibili con la necessità di abbreviare e automatizzare le procedure. Il concetto proposto in questa tesi include un sottile strato di materiale ceramico chimicamente inerte, per evitare impurità di radioisotopi. A questo scopo, sono stati proposti i materiali ceramici ad alta conducibilità termica, come parte del target plate. Per minimizzare l’energia persa sulla parte ceramica, è stato minimizzato il suo spessore. Inoltre, per mantenere una rigidità meccanica del sistema, e minimizzare i costi del target, i substrati ceramici sono stati brasati in vuoto a un backing plate di rame. Per realizzare questo prototipo, è stata studiata la brasatura in vuoto dei materiali ceramici con i metalli con diversi filler brasanti. Sono stati usati filler a base di rame in forma pastosa “home-made” per la preparazione del prototipo di target. Al fine di migliorare il contatto brasato, la parte ceramica è stata metallizzata con un sottile strato di Ti depositato con la tecnica magnetron sputtering. I prototipi di target sviluppati sono stati preparati depositando, mediante magnetron sputtering, 100µm di Mo su dischi ceramici che sono stati brasati al supporto metallico ad alta conducibilità termica (rame). I prototipi di target prodotti hanno mostrato buona stabilità termomeccanica sotto la massima potenza di fascio di protoni del ciclotrone GE PETtrace (60 µA, 15.6 MeV, densità di potenza di circa 1 kW/cm2). Sono stati realizzati test brevi (1 minuto) e test lunghi, più vicini alle condizioni di irraggiamento per la produzione. Per diminuire i costi per la produzione di 99mTc con il metodo basato su ciclotrone, è stato sviluppato un sistema per recuperare in forma metallica, il costoso 100Mo dagli scarti del modulo di separazione. In questo modo, il metodo proposto permette il recupero del MoO3 con un’efficienza del 94% partendo dallo scarto, arricchito di Mo, del modulo. La seguente riduzione dell’ossido di molibdeno, in un sistema chiuso in sovrappressione di idrogeno (senza flusso di idrogeno), fornisce più del 95% di Mo metallico. Lo stesso metodo di recupero può essere applicato per minimizzare le perdite del costoso 100Mo durante la deposizione via magnetron sputtering.
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.
Innovative PVD technologies for depositing superconducting Nb films into TESLA-type 9-cell RF cavities for particle accelerators – Giorgio Keppel PhD Thesis
Author: Giorgio Keppel; Type of thesis: PhD Thesis
Abstract: Superconducting radiofrequency resonators have become standard components inside particle accelerators. This paper proposes the research and development of copper cavities internally coated with a niobium thin film, as an alternative to the niobium bulk cavities. This R&D work is part of the ISIDE experiment, of the National Institute of Nuclear Physics, and has been carried out at the Legnaro laboratories. Specifically, at the Material Science and Technologies for Nuclear Physics Service of INFN, it has been built a new system for coating, via magnetron sputtering, a thin film of superconducting niobium inside the TESLA-type 9-cell copper resonators. The work was divided into two main areas. A first phase consisted on the design of a sputtering configuration for coating superconductive cavities based on the construction of a vacuum system using a 3D CAD software and FEM simulations in order to verify the final structure of the vacuum system. Parallel to this a phase for the construction of the induction heating apparatus was followed. Afterward, the assembly of the vacuum system was performed, with connected vacuum tests, and followed by the commissioning of the induction and pumping systems. A second phase, however, focused on the study of coating configurations, particularly on the benefits and/or problems that each configuration can lead. This study ended with the design of four different coating configurations; which will be short-tested in order to check the most suitable for coating the 9-cell copper cavity with good uniformity and excellent superconducting properties. The most promising configuration is definitely the last taken into account, which involves the use of the inductor to heat the cavity during the process and the use of an innovative cylindrical magnetron with a rotating magnet pack inside that confine the plasma on the target surface. The target consists on a Niobium tube, and the study of the magnetic configuration and at the same time rotation of magnet pack permit to have a constant deposition rate along the whole cavity (high cathode erosion rate in the cavity cell regions and low cathode erosion rate along cavity cut-off). Even if the work is still evolving and the deposition tests are just starting, what as been performed is definitely innovative and original; up to now, in literature, there are no reports of coating performed by coupling the induction heating with the magnetron sputtering. The development of a plant that allows coupling these two technologies is the main aim of this work.
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
Abstract:
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.