_:n7be865198d2247928fa4922bb18f7025xb0
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"Fast ions are an inseparable part of fusion plasmas  They can be generated using electromagnetic waves or injected into plasmas as neutrals to heat the bulk plasma and to drive toroidal rotation and current  In future power plants fusion born fast ions deliver the main heating into the plasma  Understanding and controlling the fast ions is of crucial importance for the operation of a power plant  Furthermore  fast ions provide ways to probe the properties of the thermal plasma and get insight of its confinement properties  In this thesis  numerical code packages are used and developed to simulate JET experiments for a range of physics issues related to fast ions  Namely  the clamping fast ion distribution at high energies with RF heating  fast ion ripple torque generation and the toroidal momentum transport properties using NBI modulation technique are investi gated  Through a comparison of numerical simulations and the JET experimental data it is shown that the finite Larmor radius effects in ion cyclotron resonance heating are important and that they can prevent fast ion tail formation beyond certain energy  The identified mechanism could be used for tailoring the fast ion distribution in future experiments  Secondly  ASCOT simulations of NBI ions in a ripple  eld showed that most of the reduction of the toroidal rotation that has been observed in the JET enhanced ripple experiments could be attributed to fast ion ripple torque  Finally  fast ion torque calculations together with momentum transport analysis have led to the conclusion that momentum transport in not purely diffusive but that a convective component  which increases monotonically in radius  exists in a wide range of JET plasmas  Using parameter scans  the convective transport has been shown to be insensitive to collisionality and q-profile but to increase strongly against density gradient "
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