Fast Ions in Fusion Plasmas – Towards Numerical Tokamaks

Research output: ThesisDoctoral ThesisCollection of Articles


Constructing a fusion device is a complicated, expensive, and time-consuming enterprise. To avoid costly errors in the design and operation of such a device, sophisticated predictive modelling is needed. To that end, there are several on-going projects striving towards the ambitious goal of building a numerical tokamak; i.e., a set of numerical tools that could be used to simulate the evolution of the fusion plasma through an entire discharge. In a fusion device, fast ions are born in fusion reactions. They also arise from acceleration of thermal particles using electromagnetic waves, and from injection of energetic neutrals that are ionized promptly upon entering the plasma. Fast ions are crucial for heating the plasma but they are also used for driving toroidal rotation and current. In addition, if the fast ions escape the plasma, they can pose a threat to the first walls of the device. Therefore, tools for modelling the fast ions are an integral part of any numerical tokamak. In this work, development and applications of two fast ion modelling tools, the beamlet-based neutral beam injection code BBNBI and the particle-following Monte Carlo code ASCOT, are presented. The former simulates the injection and the ionization of a neutral beam, whereas the latter models the motion and the slowing-down of fast ions in the plasma. The validity of BBNBI and ASCOT is confirmed by benchmarking them against other established neutral beam codes in Joint European Torus (JET) and ASDEX Upgrade (AUG) plasmas. The codes are then utilized to investigate (i) the losses of neutral beam injected (NBI) ions due to in-vessel coil induced magnetic perturbations in AUG, (ii) the distribution function of NBI ions in ITER, and (iii) the behaviour of fusion-born alpha particles in JET advanced scenario plasmas. Finally, the two numerical tokamak constructions into which BBNBI and ASCOT have been incorporated are introduced. While both BBNBI and ASCOT are widely used in JET Integrated Transport Code (JINTRAC), the first results utilizing them within the EFDA Integrated Tokamak Modelling (ITM) framework are presented here. The importance of orbit width effects is highlighted in a benchmark between different fast ion tools on the ITM framework. A study charting the capability of neutral beams to drive current in a future Demonstration Power Plant (DEMO) proves that BBNBI and ASCOT are capable of flexible and sophisticated modelling of NBI on the ITM framework.
Translated title of the contributionNopeat Hiukkaset Fuusioplasmoissa – Kohti Numeerisia Tokamakeja
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Groth, Mathias, Supervising Professor
  • Kurki-Suonio, Taina, Thesis Advisor
Print ISBNs978-952-60-6096-5
Electronic ISBNs978-952-60-6097-2
Publication statusPublished - 2015
MoE publication typeG5 Doctoral dissertation (article)


  • fusion
  • tokamak
  • integrated modelling
  • fast ions
  • neutral beam injection


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