MODELLING DUST FORMATION IN A FUSION DEVICE

In fusion reactors, the fuel (hydrogen isotopes) is heated to the plasma state which must be confined through extreme magnetic fields. However, confinement losses expose the reactor walls to plasma loads that cause damages and dust particles.
Dust formation is a major concern for fusion reactors performance and safety. Dust retains significant amounts of hydrogen, which affects the efficiency of the reactors losing fuel and being a potential radiation hazard if it escaped from the walls. Furthermore, due to its high chemical reactivity, it may cause explosions and damage to vessels in the case of an accidental loss of coolant or water.
Although several formation mechanisms of dust formation are well-known, such as 1) fracture and delamination of parts of deposited films and 2) remobilisation of solidified droplets of molten metal (usually beryllium) due to plasma disruptions, a more complete understanding is necessary for the choice of materials of future fusion devices.
In this project, we aim to develop a finite element model capable of simulating and predicting the fracture and delamination of deposition layers and the delamination of redeposited particles. The model will use temperature distributions derived from the thermal loads of the plasma to calculate the resulting stresses induced. The use of known values of interfacial and bulk strength and toughness will allow us to determine when and how deposition films break and interfacial decohesion occurs, and thus simulate how the dust is formed.
The model will be used for the analysis and prediction of dust formation and its behaviour in ITER, the world's largest fusion reactor, with the expectation to be of general usage and as such will be able to tackle other candidate materials and material mixes for future reactors as DEMO and STEP.
The project will be performed in conjunction with another PhD experimental project which provides data necessary for the simulations from interfacial properties of deposits and melt droplets of the JET walls, a prototype reactor previous to ITER with similar characteristics.
The student undertaking this project will be based at the Culham Centre for Fusion Energy (CCFE) and will also be a member of the Solid Mechanics and Materials Engineering Group (SMMEG) in Engineering Science with joint supervision from both organisations.

This project falls within the EPSRC Energy research area

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.