The Electron Cyclotron Resonance Heating system of the Divertor Tokamak Test (DTT) will rely on a series of mirrors to inject high-frequency millimeter waves into the reactor vessel. The last plasma-facing and steerable mirrors are crucial for transmitting the microwave beam directly into the plasma while sustaining the harsh conditions in the ECRH ports. In particular, the main challenges faced by the mirrors are magnetic torques that may interfere with the steering mechanism, intense heat load, and high fluxes of energetic neutrals. It is therefore essential to develop mirrors capable of reducing magnetic torques and dissipating heat while remaining effective in microwave reflection and resistant to erosion by energetic particles, all without increasing ohmic losses associated with surface roughness. An approach currently under investigation involves combining a dielectric ceramic substrate with a tungsten coating. Since the design of the coating is fundamental in determining the performance and lifetime of the component, this project focuses on the production of tungsten layers with optimal characteristics for DTT’s ECRH. The project was conducted at the Istituto per la Scienza e Tecnologia dei Plasmi (ISTP-Milano) and began with the deposition of three types of tungsten multilayers on samples of ceramic substrates using radio-frequency magnetron sputtering. Coatings were investigated in morphology, composition, adhesion, and electrical resistivity, and then exposed to DTT-relevant plasma in the GyM linear device. Post-exposure samples were analyzed with morphological and electrical characterization, mass loss quantification, and sputtering yield calculations. The coatings showed good adhesion and maintained their topography and roughness after plasma exposure, without significant differences among the three types of coatings produced. The comparison of sputtering results with an established semi-empirical model suggested a mechanism for erosion enhancement. Considerations on the role of coating impurities in the increase of sputtering involved preliminary simulations with SRIM-2013. Additionally, estimations of ohmic losses were performed based on experimental data, providing an idea of the extent of this phenomenon. As one of the first experimental attempts to produce tungsten coatings on ceramic samples for DTT’s ECRH, the results obtained in this project serve as a viable foundation for future research.
Il sistema di Electron Cyclotron Resonance Heating (ECRH) del Divertor Tokamak Test (DTT) userà una serie di specchi per introdurre microonde nel volume del reattore. Gli ultimi specchi, rivolti verso il plasma e orientabili, devono trasmettere il fascio di onde nel plasma resistendo alle condizioni estreme dei port del sistema. In particolare, le principali sfide sono i momenti magnetici, che potrebbero interferire con il meccanismo di orientamento, intensi carichi termici e flussi di neutri energetici. Quindi, è fondamentale sviluppare specchi in grado di ridurre i momenti magnetici e dissipare calore, mantenendo una buona riflessione delle microonde e resistendo all’erosione senza aumentare le perdite ohmiche connesse alla rugosità. Un approccio in fase di studio prevede l'uso di un substrato in ceramica con un rivestimento in tungsteno. Poiché il design del rivestimento è determinante per le prestazioni e la durabilità del componente, questo progetto si concentra sulla produzione di uno strato di tungsteno con caratteristiche ottimali per l’ECRH di DTT. La ricerca è stata condotta presso l’Istituto per la Scienza e Tecnologia dei Plasmi (ISTP-Milano) e ha avuto inizio con la deposizione di tre tipi di multilayer di tungsteno su campioni ceramici mediante magnetron sputtering a radiofrequenza. I rivestimenti sono stati analizzati in morfologia, composizione, adesione e resistività elettrica, e poi esposti a plasma rilevante per DTT nel dispositivo lineare GyM. Dopo l’esposizione, i campioni sono stati caratterizzati di nuovo, si è misurata la perdita di massa e si sono calcolati i rendimenti di sputtering. I rivestimenti hanno mostrato una buona adesione e hanno mantenuto la loro topografia e rugosità dopo l’esposizione, senza differenze significative tra le diverse tipologie prodotte. Il confronto tra i risultati di sputtering e un modello semi-empirico ha suggerito un meccanismo di aumento dell’erosione. Considerazioni sul ruolo delle impurità del rivestimento nell'aumento dello sputtering hanno incluso simulazioni preliminari con SRIM-2013. Inoltre, dai dati sperimentali sono state stimate le perdite ohmiche per dare un'idea della portata del fenomeno. Essendo uno dei primi esperimenti di produzione di rivestimenti in tungsteno su campioni ceramici per l’ECRH di DTT, i risultati di questo progetto costituiscono una base valida per ricerche future.
Production and analysis of metallic coatings on ceramic substrates for the Electron Cyclotron Heating launching mirror of DTT
Buzzoni, Alice
2024/2025
Abstract
The Electron Cyclotron Resonance Heating system of the Divertor Tokamak Test (DTT) will rely on a series of mirrors to inject high-frequency millimeter waves into the reactor vessel. The last plasma-facing and steerable mirrors are crucial for transmitting the microwave beam directly into the plasma while sustaining the harsh conditions in the ECRH ports. In particular, the main challenges faced by the mirrors are magnetic torques that may interfere with the steering mechanism, intense heat load, and high fluxes of energetic neutrals. It is therefore essential to develop mirrors capable of reducing magnetic torques and dissipating heat while remaining effective in microwave reflection and resistant to erosion by energetic particles, all without increasing ohmic losses associated with surface roughness. An approach currently under investigation involves combining a dielectric ceramic substrate with a tungsten coating. Since the design of the coating is fundamental in determining the performance and lifetime of the component, this project focuses on the production of tungsten layers with optimal characteristics for DTT’s ECRH. The project was conducted at the Istituto per la Scienza e Tecnologia dei Plasmi (ISTP-Milano) and began with the deposition of three types of tungsten multilayers on samples of ceramic substrates using radio-frequency magnetron sputtering. Coatings were investigated in morphology, composition, adhesion, and electrical resistivity, and then exposed to DTT-relevant plasma in the GyM linear device. Post-exposure samples were analyzed with morphological and electrical characterization, mass loss quantification, and sputtering yield calculations. The coatings showed good adhesion and maintained their topography and roughness after plasma exposure, without significant differences among the three types of coatings produced. The comparison of sputtering results with an established semi-empirical model suggested a mechanism for erosion enhancement. Considerations on the role of coating impurities in the increase of sputtering involved preliminary simulations with SRIM-2013. Additionally, estimations of ohmic losses were performed based on experimental data, providing an idea of the extent of this phenomenon. As one of the first experimental attempts to produce tungsten coatings on ceramic samples for DTT’s ECRH, the results obtained in this project serve as a viable foundation for future research.| File | Dimensione | Formato | |
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2025_12_Buzzoni_Tesi.pdf
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2025_12_Buzzoni_Executive_Summary.pdf
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Descrizione: executive summary
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https://hdl.handle.net/10589/247450