1,721,249 research outputs found
Creation, validation and application of a collisional radiative model for positive argon ions
Full text linkThe main goal of this thesis is the creation and development of a collisional radiative model for Ar+, based on the flexible package Yacora, to be used as a diagnostic for the line of sight averaged electron density and temperature in a plasmaope
Investigation of ELISE beam properties by means of the diagnostic calorimeter
Full text linkNegli ultimi anni molti studi sono stati dedicati allo sviluppo di iniettori di particelle neutre (NBI) come sistema per riscaldare e indurre una corrente in plasmi termonucleari, avendo come riferimento l'esperimento internazionale sulla fusione ITER. Questa tesi si concentra sulla caratterizzazione del fascio di neutri della test facility ELISE di IPP, che rappresenta un passo importante nello sviluppo di NBI per ITER. Lo studio, svolto mediante il calorimetro diagnostico, è rivolto particolarmente alla determinazione di potenza, divergenza e omogeneità del fascio.ope
Characterisation of a 2 MHz driven inductively coupled plasma generator for H-production
No full textThe accelerator complex of CERN (Switzerland) is currently the subject of an upgrade comprising a new injector, namely the linear accelerator Linac4. Not only is this new accelerator going to provide higher energetic beams than its predecessor Linac2, increasing from 50 MeV to 160 MeV, but also will it operate with negatively charge hydrogen ions instead of pure proton beams. This is the key feature towards a major improvement of beam injection into the PS Booster and better beam quality. The ion source delivering this negative hydrogen beam is based on the volume RF H- source developed at DESY which should suffice Linac4 specifications of an 80 mA H- beam at 45 keV a pulse length of 0.4 ms and a repetition rate of 2 Hz. In a recent study the Linac4 accelerator serves as the first stage of a 430 meter long superconducting linac, the SPL. This accelerator design demands a different source beam viz. an 80 mA at 45 keV, an increased pulse length of ~1.2 ms and a repetition rate of 50 Hz, increasing the duty factor to 6%. This requires a redesign of the Linac4-DESY source to meet the SPL specifications. This thesis deals with an evolution of the Linac4-DESY ion source to develop a new version, which satisfies SPL requirements. As a consequence a new plasma generator (PG) has been designed and constructed.Der Beschleunigerkomplex des europäischen Forschungszentrums CERN (Schweiz) wird gerade um einen neuen Injektor, dem Linac4 Linearbeschleuniger, erweitert. Dieser Beschleuniger soll den gegenwärtigen Linac2 Injektor ersetzen und einen Teilchenstrahl von 160 MeV statt der bisherigen 50 MeV, zur Verfügung stellen. Zusätzlich wird der neue Linac mit negativ geladenen Wasserstoffionen betrieben anstatt des üblichen Protonenstrahls. Dies ist einer der Hauptgründe für die verbesserte Strahlinjektion in den nachfolgenden PS Booster sowie der verbesserten Strahlqualität. Die Ionenquelle welche den negativen Wasserstoffstrahl mit nomineller Intensität von 80 mA bei einer Teilchenenergie von 45 keV, einer Pulslänge von 0.4 ms sowie einer Wiederholrate von 2 Hz liefern soll basiert auf einer Ionenquelle welche am deutschen Beschleunigerzentrum DESY (Hamburg) entwickelt wurde. Eine gegenwärtige Studie beschäftigt sich mit einem Upgrade des Injektors, welches den Linac4 Beschleuniger als erstes Element eines 430 Meter langen supraleitenden Linearbeschleunigers (SPL) sieht. Dieses Beschleunigerdesign stellt andere Anforderungen an den von der Quelle zur Verfügung gestellten Strahl: neben einem unveränderten Ionenstrom von 80 mA bei einer Energie von 45 keV, sollen Pulse von 1.2 ms Länge mit einer Wiederholrate von 50 Hz extrahiert werden was das Tastverhältnis auf 6% erhöht und eine Neugestaltung der Linac4-DESY Quelle verlangt um den anspruchsvollen Spezifikationen zu genügen.Diese Doktorarbeit beschäftigt sich mit der Weiterentwicklung der Linac4-DESY Quelle um eine Version zu entwickeln welche den SPL Anforderungen genügt. Als Konsequenz wurde ein neuer Plasmagenerator (PG) entwickelt und konstruiert
IR thermography analysis of the powerful hydrogen beam at ELISE
Full text linkThermonuclear fusion will supply the world with a safe, environmentally friendly energy source. Neutral beam injectors (NBI) provide a heating system and a current drive system for thermonuclear plants. The deuterium-tritium mixture that consists in the fuel of such thermonuclear reactors is in a plasma state and it is magnetically confined in a toroidal-shaped vessel. In ITER, the international thermonuclear experimental reactor, under realisation in Cadarache (FR), two NBI of 16.5 MW each will be installed. The ITER-like neutral beam injector described in section 1.3 is based on H-/D- RF source whose design was developed at the Max-Planck Institut fur Plasmaphysik (IPP). The use of negative ions is mandatory to reach high neutralisation efficiencies in case of beams of 1MeV energy (ITER requirements). In the source a plasma is ignited by means of RF coils, then the beam is formed and accelerated by a grid system. The extraction and acceleration stages consist in potential steps applied to grids disposed perpendicularly to the beam-line. At the IPP are present a 1/8 ITER-size prototypes and the test facility ELISE (1/2 ITER-size source) that aims to investigate the physics behind the ion sources with an extraction area is about 1000 cm2. ELISE, whose design and beam diagnostics are described in chapter 2, is an important step between small-scale prototypes and the full size ITER source. This thesis aims to characterize the beam properties of ELISE, in particular the beam width and the beam deflection, in different operational conditions by means of the IR analysis of the beam profile on a diagnostic calorimeter. The analysis described in 3.2 is automatized and the beam parameters measured from the beam imprint on the calorimeter are automatically collected in a database. The emissivity calibration was performed using the temperature measured by thermocouples embedded on the calorimeter. In section 3.3 a initial cross-check with other beam diagnostics is performed in order to test the reliability and the robustness of the analysis. The beam parameters retrieved from the IR analysis are investigated as a function of operational parameters in chapter 4. The effects of the beam optics, acceleration potential and the pressure on the beam are studied in sections 4.1, 4.2 and 4.3. The plasma in the source is modified by means of applied electric and magnetic fields and by external magnets installed inside the source. The IR evaluation results as a function of operational parameters corresponding to the electric and magnetic field are discussed in sections 4.5, 4.6 and 4.4. The beam emission spectroscopy (BES) is a beam diagnostics that provides the beam divergence by means of the analysis of the Hα Doppler peak. The beam width retrieved by the beam imprint on the calorimeter and the beam divergence measured by the BES are compared. The spectra of BES indicate the presence of an additional broad component in the beam divergence that is investigated by means of the external portions of the diagnostic calorimeter. The cross-checks and analyses are described in section 4.7.ope
Beam calorimetry at the large negative ion source test facility ELISE: Experimental setup and latest results
Full text linkInvestigation of principal reactive pathways in CO2 plasmas by numerical techniques
Full text linkA resource-efficient Europe is the flagship initiative of the Europe 2020 strategy, with the CO2 emissions control as its backbone activity. Within this framework, the main idea of this study is to investigate a novel approach that aims to convert biogas into chemicals and fuels. Central in the approach, is the use of a plasma to store energy in chemical bonds. This thesis presents a study on principal pathways in a CO2 plasma and a first application of numerical reduction techniques to reduce the chemistry.ope
Application of collisional radiative models for atomic and molecular hydrogen to a negative ion source for fusion
Full text linkI modelli di popolazione descrivono come dipendono i parametri di plasma (densità e temperature elettronica) dalla densità degli stati eccitati di molecole o atomi in un plasma.
Il più semplice modello di popolazione è chiamato modello a corona e bilancia solamente l’eccitazione dallo stato fondamentale dovuta a collisioni tra elettroni e atomi (o molecole) con l’emissione spontanea. Questo modello è valido per plasmi con bassa denistà elettronica (minore di 10^16 m^(-3)). Per densità eletroniche elevate (maggiori di 10^22 m^(-3)), si può applicare la condizione di equilibrio termodinamico (LTE) e le densità di popolazione dei diversi stati eccitati seguono la distribuzione locale di Boltzmann. Il lavoro di tesi riguarda un terzo tipo di modello di popolazione, chiamato modello collisionale radiativo, che è applicato per valori intermedi di densità elettronica. I modelli collisionali radiativi consistono in un insieme di equazioni differenziali accoppiate che bilanciano tutti i processi di eccitazione e diseccitazione.
L’obiettivo principale di questo lavoro è l’uso di diversi modelli collisionali radiativi basati su YACORA per caratterizzare il plasma all’interno dei drivers dell’esperimento ELISE, attualmente in funzione presso il Max Planck Institut für Plasmaphysik in Garching (Monaco di Baviera). ELISE è dotata di una sorgente in radiofrequenza per la produzione di ioni negativi di idrogeno e deuterio, generati in un plasma a bassa pressione e temperature.
Per stimare la temperatura e la densità elettronica in ELISE sono applicati i modelli collisionali radiativi per H e H2 presenti in YACORA con cui vengono calcolate le emissività da confrontare con quelle misurate tramite la spettroscopia ottica di emissione. Sono considerati due metodi basati sul confronto tra le emissività misurate e calcolate: il primo è basato sul rapporto tra le intensità di alcune linee di emissione selezionate, mentre il secondo usa direttamente il valore assoluto di queste linee di emissione. Il primo metodo può essere usato anche con una diagnostica spettroscopica non calibrata in modo assoluto, ma restituisce una stima meno precisa del secondo, che, tuttavia, richiede la misura delle intensità in modo assoluto. L’analisi è condotta sia in idrogeno che in deuterio.
Come ulteriore applicazione del modello collisionale radiativo per l’elio in YACORA, è stata determinata la densità e la temperatura elettronica di un plasma d'elio.
Un altro importante obiettivo di questo lavoro di tesi, direttamente connesso con quello precedente, è stato lo sviluppo di un'applicazione web completa con lo scopo di rendere pubblico l’utilizzo dei modelli collisionali radiativi per H, H2 e He basati su
YACORA. Attraverso il sito web, un utente può inserire i parametri di ingresso richiesti da yacora. Dopo l’approvazione da parte di un reviewer, il calcolo può iniziare. Alla fine del calcolo, i risultati di yacora sono caricati nella cartella personale dell’utente all’interno del sito web (www.yacora.de).ope
First hydrogen operation of NIO1: Characterization of the source plasma by means of an optical emission spectroscopy diagnostic
Full text linkSpektroskopische Untersuchung und Modellierung von mikrowellen-angeregten Silanplasmen
Full text linkIn dieser Arbeit werden mikrowellen-angeregte Silanplasmen im Druckbereich von 2 - 20 Pa mit Diagnostikmethoden, die das Plasma nicht beeinflussen, detailliert untersucht. Dabei handelt es sich um Plasmen aus reinem Silan, Mischungen von Silan mit Argon oder Helium sowie Mischungen mit Wasserstoff, die in der Praxis zur Abscheidung von a-Si:H Schichten verwendet werden. Die Plasmaparameter wie Elektronentemperatur, Gastemperatur und Rotationstemperatur verschiedener angeregte Zustände werden mit der Emissionsspektroskopie ermittelt. Die Niederdruckplasmen befinden sich nicht im thermischen Gleichgewicht und die Interpretation der Spektren erfordert daher spezielle Modelle. Hier wird das Koronagleichgewicht verwendet. Die Elektronendichte wird mit einem Mikrowelleninterferometer bestimmt. Messungen mit einem Massenspektrometer geben Aufschluss über die Silanteilchendichte im Plasma, über die aus dem Silan gebildete Disilandichte und über den im Plasma vorhandenen molekularen Wasserstoff. Absolutmessungen der Strahldichte von Spektrallinien und Molekülbanden ermöglichen die Bestimmung von Teilchendichten zugänglicher Radikale (SiH, Si, H2, H) unter Verwendung des Koronamodells und bei Kenntnis der Plasmaparameter. Kombiniert werden diese Ergebnisse mit einer Modellierung der Silanplasmen, die sowohl in der gemessenen Elektronentemperatur als auch in den Teilchendichten aus der Massenspektrometrie überprüft werden kann. Ein Vergleich der Modellierung mit den Ergebnissen aus der Emissionsspektroskopie soll die Anwendbarkeit der Emissionsspektroskopie zur Teilchendichtebestimmung demonstrieren und die Modellierung in weiteren Teilchendichten bestätigen. Nach einer experimentellen Verifizierung des Modells kann dann auf die nicht zugänglichen Teilchendichten wie SiH3 oder SiH2 oder auf die Ionenzusammensetzung der Plasmen geschlossen werden
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