Reduced transport modelling of fast ions in MAST Upgrade

In fusion plasmas, fast ions have energies much higher than the thermal plasma background. Fast ions are generated by external auxiliary heating such as Neutral Beam Injection (NBI) and Ion Cyclotron Resonance Heating
(ICRH) or by the fusion reactions themselves. In the former cases, fast ions are hydrogen isotopes with energies in the range from tens of keVs up to a few MeVs. Fusion reactions produce, in addition to hydrogen isotopes, alpha particles with energies in the MeV range.Fast ions play an important role in heating the plasma, maintaining the high temperatures necessary to sustain the fusion reactions and crucial in achieving a burning plasma. NBI heating is also important for current drive, that is for long pulse operation of tokamaks beyond the inductive regime and therefore for the realization of a fusion reactor.Confining fast ions in the plasma for time long enough so that they can transfer their energy to the background plasma is therefore crucial for achieving the goal of a power plant based on thermonuclear fusion reactions. However, fast ion confinement is degraded by plasma instabilities some of which are triggered by the fast ion themselves. In this case, energy exchange between the fast ions and the instabilities result in the redistribution and loss of fast ions, ultimately reducing the performances of fusion reactors. Furthermore, the loss of fast ions in the plasma can result in the damage of the reactor first wall, an issue particularly for the very energetic alpha particles that will be produced in ITER and DEMO.The interaction between FIs and MHD instabilities is an active and intense field of research Recent modelling developments include MHD and particle kinetics codes (with realistic description of the instabilities' amplitude and spatial structure and full orbit calculations) such as HALO (developed at CCFE) and the reduced transport "kick-model" for TRANSP/NUBEAM (developed at PPPL). Of particular importance, especially for MAST Upgrade, is the modelling of the FIs full orbits for the validation of theoretical predictions of the interplay between FIs and MHD instabilities such as sawteeth, fishbones, toroidal Alfvén eigenmodes, long-lived modes and edge localized modes. The spatial structure and temporal evolution of these instabilities, at times non-linearly coupled to the dynamics of the FIs, is crucial for the correct prediction of the confinement of FIs. The project is aimed at a systematic comparison of full-orbit and guiding-center reduced transport calculations with a set of fast ions experimental measurements on MAST Upgrade in presence of perturbations of the plasma equilibrium due to sawteeth, TEAs and fishbones. A particular focus will be dedicated to the modelling and interpretation of collimated neutron flux measurements using the upgraded neutron camera installed on MAST Upgrade and the comparison with other FI diagnostics (FILD, FIDA, compact NPA and charged fusion product detector). This is a modelling project for which good numerical computation skills are required. The research will be carried out mainly at Durham University with collaborations with CCFE (for HALO), the Princeton Plasma Physics Laboratory (for TRANSP/NUBEAM) and Aalto University (for ASCOT). The outcome of this project is a framework of reduced, rapid fast ion transport models that will be used to compare simulations and measurements probing different regions of the phase space thus providing an integrated understanding of the FIs dynamics. In turn, the outcome of this project will enable the development of operating scenarios where the effect of performance limiting distributions will be suppressed thus allowing improved FI confinement and non-inductive current drive. The main focus of this project is MAST Upgrade thanks to its on-axis/off-axis NB injection flexibility but the developed framework will be applicable to conventional tokamaks and will be of relevance to STEP, ITER and DEMO.

Identifying a sustainable energy supply is one of the biggest challenges facing humanity. Fusion energy has great potential to make a major contribution to the baseload supply - it produces no greenhouse gases, has abundant fuel and limited waste. Furthermore, the UK is amongst the world leaders in the endeavour to commercialise fusion, with a rapidly growing fusion technology and physics programme undertaken at UKAEA within the Culham Centre for Fusion Energy (CCFE). With the construction of ITER - the 15Bn Euro international fusion energy research facility - expected to be completed in the middle of the 2020's, we are taking a huge step towards fusion power. ITER is designed to address all the science and many of the technology issues required to inform the design of the first demonstration reactors, called DEMO. It is also providing a vehicle to upskill industry through the multi-million pound high-tech contracts it places, including in the UK.
ITER embodies the magnetic confinement approach to fusion (MCF). An alternative approach is inertial fusion energy (IFE), where small pellets of fuel are compressed and heated to fusion conditions by an intense driver, typically high-power lasers. While ignition was anticipated on the world's most advanced laser fusion facility, NIF (US), it did not happen; the research effort is now focused on understanding why not and the consequences for IFE, as well as alternative IFE schemes to that employed on NIF.

Our CDT is designed to ensure that the UK is well positioned to exploit ITER and next generation laser facilities to maximise their benefit to the UK and indeed international fusion effort. There are a number of beneficiaries to our training programme: (1) CCFE and the national fusion programme will benefit by employing our trained students who will be well- equipped to play leading roles in the international exploitation of ITER and DEMO design; (2) industry will be able to recruit our students, providing companies with fusion experience as part of the evolution necessary to prepare to build the first demonstration power plants; (3) Government will benefit from a cadre of fusion experts to advise on its role in the international fusion programme, as well as to deliver that programme; (4) the UK requires laser plasma physicists to understand why NIF has not achieved ignition and identify a pathway to inertial fusion energy.

As well as these core fusion impacts, there are impacts in related disciplines. (1) Some of our students will be trained in low temperature plasmas, which also have technological applications in a wide range of sectors including advanced manufacturing and spacecraft/satellite propulsion; (2) our training in materials science has close synergies with the advances in the fission programme and so has impacts there; (3) AWE require expertise in materials science and high energy density plasma physics as part of the national security and non-proliferation strategy; (4) the students we train in socio-economic aspects of fusion will be in a position to help guide policy across a range of areas that fusion science and technology touches; (5) those students involved in inertial fusion will be equipped to advance basic science understanding across a range of applications involving extreme states of matter, such as laboratory astrophysics and equations of state at extreme pressures, positioning the UK to win time on the emerging next generation of international laser facilities; (6) our training in advanced instrumentation and control impacts many sectors in industry as well as academia (eg astrophysics); (7) finally, high performance computing underpins much of our plasma and materials science, and our students' skills in advanced software are valued by many companies in sectors such as nuclear, fluid dynamics and finance.