Abstract
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 ripplefield 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.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
|
Award date | 9 Nov 2012 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 978-951-38-7467-4 |
Electronic ISBNs | 978-951-38-7468-1 |
Publication status | Published - 2012 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- JET
- tokamak
- fusion
- energy
- plasma
- toroidal rotation
- momentum transport
- fast ions
- neutral beam injection
- NBI