Researching the means to create an inexhaustible source of clean, large scale, energy for the continued growth of mankind is arguably the top long-term priority for humanity. When considering the global concerns regarding: (i) increasing energy demand due to rising population levels, (ii) rising global sea levels and temperatures, (iii) the inevitable depletion of existing fossil fuel deposits and (iv) political issues arising with the use of fossil-fuels and present-day nuclear power, the argument for continued nuclear fusion research becomes clear.

Solving the exponential energy crisis as the world collectively develops and becomes more energy intensive will ensure humanities continued ability to flourish technologically and culturally without concern for large energy consumption. Intensive industries aimed at reducing our growing carbon footprint such as electric arc furnaces for steel production and desalination plants for agriculture will require high yield, low carbon energy. The process of nuclear fusion has significant advantages over its competitor nuclear fission, notably the risk of severe accidents like those at Chernobyl and Fukushima Daiichi which led to cancer increases among the population, and the radioactive waste produced by fusion is calculated to be smaller than that of fission plants.

Producing this near inexhaustible source of low carbon energy, following the example noted in of a Deuterium and Tritium reaction producing an energy of 17.6MeV with each fusion event, requires several technological challenges to be overcome before successful commercial operation of a plant can commence. For the above example of a Deuterium and Tritium reaction to occur: “the two nuclei must have enough energy to overcome the repulsive Coulomb force acting between the nuclei and approach each other sufficiently close that the short-range attractive nuclear force becomes dominant”. This repulsive Coulomb force between the nuclei is overcome through the heating of said nuclei to temperatures in excess of 5 ∗ 107K, it is this extreme temperature that produces the plasma which must be confined.

The issues associated with this plasma are as follows: (i) plasma confinement, (ii) reactor materials, and (iii) heat removal. The challenge focused on in this dissertation is the material selection for the plasma confinement chamber used in fusion plants. The materials required to build a plasma facing wall, designed to protect the magnets which produce the toroidal and poloidal magnetic fields, need to be survivable against high temperatures and have low neutron irradiation properties. Because of these requirements, low neutron activation steels are being examined in this dissertation for their suitability in plasma confinement chamber walls.

The physics involved in plasma confinement chambers is not the focus of this project, however it will be noted briefly the reasons as to why the physics of plasma itself causes great issue when choosing a suitable material for the walls of its confinement chamber. The environment produced to confine plasma as stated above is one of a strong magnetic field, this requires us to examine the effect the electromagnetic fields have on the structural components. In addition to dealing with the high electromagnetic field, the materials used to line the wall of the confinement chamber are also subjected to “high particle and neutron flux and high heat loads” . The materials chosen for this dissertation, outlined below, are solely chosen to test their change in material characteristics whilst under the influence of a magnetic field, as such the concern regarding their change in material behaviour whilst under heavy neutron bombardment and subsequent irradiation is not considered.

The materials must have a “high thermal conductivity for efficient heat transport, high cohesive energy for low erosion by particle bombardment and low atomic number” . Such materials used in this dissertation emit these qualities, the Nickel Alloy 718 has a high thermal conductivity of 9.3 – 11.5 W/mK at room temperature and P91 Steel has a high thermal conductivity of 26 W/mK at room temperature.

The magnetic field produced by the reactor’s confinement chamber is designed to stop the very hot plasma from being quenched when in direct contact with an ordinary container wall. It is for these requirements, to preserve the critical temperature for significant fusion yield, which must surpass the Lawson parameter, and with the “product of density and confinement time” being critical for this successful fusion ignition, we can outline the parameters of this dissertations experiment, focusing on the magnetic field effects of the structural materials.

This project, as a continuation of the work already commissioned by UKAEA and completed by University of Bristol Technical Specialist Mehdi Mokhtarishirazabad, uses the same tensile samples. Produced by the University of Bristol Engineering Workshop. These samples are in accordance with the agreement made between the UOB and UKAEA, they had a gauge length to gauge diameter ratio of 3 which meets ASTM-E2714.

To measure the extension in gauge length of each sample, a video extensometer (RTSS by LIMESS) was required, which monitors the difference in length between two markings. The process by which the vide extensometer deciphers these two markings is as follows: The sample is painted in a bright white coating, and two markings are made that create sharp black rings around the sample. The contrast between the white paint and the black marking is noted on the video extensometers mono-chromatic filter. Using an algorithm it notes the change in grey shading on the sample and can calculate where a sharp edge is, using this sharp edge the video extensometer can lock onto the two markings of the sample and record the extension between these two markings as the tensile test is undertaken.

By using the video extensometer a fast strain measurement could be taken with the camera operating at a peak framerate of up to 500Hz. The sample markings were 11 measured beforehand and noted as being 4.5mm for each sample, however due to problems during sample preparation some samples had different marking distances with an error of plus 0.5mm.

To create the white surface and two black markings on the samples, the sample gauges were painted with a layer of matt white high temperature primer (VHT SP118). To protect the threaded ends of the samples, to avoid issues when inserting into the accurately machined parts of the tensile rig, masking tape was applied to the ends of each sample. The sample were then mounted into a Dremel 3000 rotary tool and rotated with a speed of 10000 rpm, the VHT paint was applied using an airbrush. With the sample now coated with a uniform layer of the VHT paint. Two dots were created to show the bare metal of the sample using Vernier Calliper. A piece of dental floss was stripped to small individual strands, these strands were held by the student and applied to the sample on the marked dots whilst the sample was spun in the Dremel 3000. The application of pressure from the dental floss strands removed the layer of VHT paint, revealing the dark metal surface of the sample in a ring shape. The distance and quality of these sample markings were checked using an Optimax microscope. The advantage of using this type of paint is even after deformation during tensile testing, the markings retain their clarity for the video extensometer, allowing for continued recording of gauge length extension.