Abstract of thesis
Thermonuclear fusion is a potential candidate for providing a clean source of energy and satisfying the high electricity demands of the future. The fuel in a typical reactor is heated to a very high temperature forming a gas of charged particles known as a plasma. The plasma has to reach a self-sustainable regime to minimise the input power required to drive the reactor. Reaching this regime demands a sufficiently low transport of energy, which remains one of the biggest challenges in plasma physics today. Turbulence driven by small scale instabilities causes large heat and particle transport and is a major limiting factor of current fusion devices. Above a critical value, the ion temperature gradient increases the growth of a microinstability - the ion temperature gradient mode- believed to dominate the ion energy transport.
It has recently been discovered that energetic ions generated by auxiliary heating may reduce the growth of this instability. By applying the gyrokinetic formalism and performing linear simulations using the local continuum gyrokinetic code GS2, we explore the linear physics of this stabilising effect. In order to isolate important effects due to the presence of fast ions, we make use of the flexibility of GS2 to consider approaches of changing the plasma and magnetic geometry parameters independently. We assess the possibility to neglect magnetic geometry changes to simplify the analysis, by investigating its contribution to the stabilising effect. For the cases studied we find that the Shafranov shift and safety factor profile might have to be taken into account. For fixed density and temperature a destabilising influence of the fast ion density gradient is found, while the high temperature gradient is stabilising, both as predicted by analytical models. A large part of the observed stabilisation comes from the contribution to the ratio of the total thermal to magnetic pressure. In addition, the effect of this ratio is enhanced because of the large density and temperature gradients of the fast ions. We investigate the role of hot ion mass and charge in order to evaluate the stabilisation of different types of hot ions. Finally, the possibility of adjusting the electron and ion profiles to account for the presence of fast ions without including them as a kinetic species, is considered.
Student project presentation
N6115 seminar room, Origo building 6th floor, Fysikgården 1
18 May, 2017, 10:00
18 May, 2017, 11:00