Fusion Energy (Inertial and Magnetic Confinement)

Fusion is a potential source of abundant, zero-carbon-emission and low-waste energy, and a sustainable long-term solution to the world’s energy needs. There are significant challenges ahead to realise fusion as a commercial energy source and the timescales are uncertain. However, the global potential of fusion energy is motivating international projects in fusion energy research. Researchers at SUPA institutions are playing important roles in these research programmes.

What is fusion?

Fusion is the nuclear reaction process which powers the sun. It occurs when light atomic nuclei, overcome the repulsive Coulomb force between them, fuse into heavier nuclei releasing a huge amount of energy in the process. The high temperature and pressure conditions required to enable this are achieved by confining fuel in the form of a plasma – a gas of charged particles produced when electrons are separated from their nuclei and move independently. The plasma must be heated to temperatures above 100 million °C to achieve fusion reaction rates high enough to produce a useful energy source. Typically deuterium and tritium, two isotopes of hydrogen, are used as the fuel. These nuclei fuse to form a helium nucleus, and in the process release large amounts of energy in the form of high energy neutrons. A total of 17.6MeV (megaelectron volts) of energy is released per reaction. The energy carried by the neutrons can be slowed down in a blanket surrounding the reaction chamber and the resultant heat could produce steam to drive turbines in a commercial fusion power station.

Confinement of the plasma is important to sustain and control fusion reactions in the laboratory long enough for fusion to work as an energy source. There are two main approaches to achieve that, inertial (laser-) confinement and magnetic confinement and SUPA researchers are working on both approaches.

Inertial (Laser-) Confinement Fusion

Inertial Confinement Fusion(ICF) is a process in which a millimeter-size pellet containing the deuterium and tritium fuel is heated and compressed for a very short period of time to achieve the temperature and pressure conditions required for fusion reactions to occur. The energy to compress and heat the fuel is delivered to the outer layer of the pellet using high energy laser beams. The outer layer is heated and ablated, producing a reaction force in the form of a shock wave which travels inwards to compress and heat the fuel at the centre to initiate fusion reactions. With sufficient heating and compression an “ignition” fusion burn wave is achieved in which a significant proportion of the fuel is burnt.

The Fast Ignition (FI) approach to ICF involves the use of ultra-short duration high intensity laser pulses to ignite the fuel core that has been compressed by longer laser pulses. This scheme holds the promise of reducing the laser drive energy required to achieve ignition, and hence improve the overall efficiency of inertial confinement. FI is a major focus of research at several laser laboratories around the world and is central to the UK-led EU FP7 Roadmap project, HiPER (High Power laser Energy Research), which started in 2008.

Researchers at Strathclyde are investigating the physics of laser energy transfer and heating of plasma via the generation and transport of high flux, high energy beams of electrons and ions. This physics underpins the Fast Ignition approach to laser-fusion and is funded by EPSRC, STFC and the HiPER project.

Magnetic Confinement Fusion

In Magnetic Confinement Fusion (MCF) strong magnetic fields are used to confine the deuterium and tritium plasma and avoid contact with the walls of the containment vessel. Much of the effort in magnetic confinement has been based on the tokamak (“donut” shaped bottle) design. A current is driven through the plasma to create a magnetic field, which together with a toroidal field confines the high temperature plasma. Tokamak fusion reactors would operate in steady state.

Significant progress has been made towards producing a “burning” plasma. Much of this work has been carried out at the Joint European Torus (JET) facilities in the UK. Sixteen megawatts of fusion power has been achieved and strides have been made in controlling the behaviour of the confined plasma. This has been achieved through advances in our understanding of plasma turbulence, and stable operating regimes.

Strathclyde researchers provide primary atomic physics data and modelling used to investigate the physics of plasma magnetic confinement and energy loss mechanisms. This work is carried out in collaboration with the Culham Centre for Fusion Energy (CCFE) and is funded by EPSRC and EURATOM.