Runaway electrons in tokamak disruptions in the presence of impurities

Typ
Examensarbete för masterexamen
Master Thesis
Program
Publicerad
2013
Författare
Capone, Luigino
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Disruptions in tokamak devices are phenomena where the plasma loses its confinement suddenly, on time scales of a few milliseconds, releasing most part of the plasma energy onto the machine components. These phenomena are dangerous to the plasma-facing components and they pose a severe threat to the machine's integrity, causing the deposition of intense thermal fluxes on the first wall materials and serious electromagnetic stresses on the structure. High-energy runaway electrons are also generated due to disruptive phenomena, causing further damage to the machine. The recent successful installation of the JET ITER-like wall (ILW) in place of the previous carbon-based wall, suggests an assessment of the impact of different wall composition on the runaway production. Extracting experimental data from two different plasma discharges equipped respectively with beryllium and carbon wall, the production of runaway electrons has been investigated through a numerical code. Simulations for the evolution of runaway electrons have been carried out for different scenarios, considering both a prescribed exponential temperature decay and disruptions triggered by an argon injection scenario. Argon and carbon/beryllium impurities coming from the sputtering of the first wall has also been included in a further scenario. A comparison of two different discharges in terms of generation mechanisms for runaways has also been performed, together with various scans for different argon concentrations. Simulations showed that impurities coming from different walls, have a different impact on the produced runaway currents and on generation mechanisms.
Beskrivning
Ämne/nyckelord
Fysik, Physical Sciences
Citation
Arkitekt (konstruktör)
Geografisk plats
Byggnad (typ)
Byggår
Modelltyp
Skala
Teknik / material