Development of a Tungsten-Diamond Composite for High Heat-Flux Plasma Facing Components (materials strand project)

Supervisor/s – Aneeqa Khan, Ed Pickering & Paul Mummery (University of Manchester). Yiqiang Wang (UKAEA), David Bowden (UKAEA) & Steve Lisgo (Independent).

Laboratory production and testing of a next-generation, high heat-flux tolerant, self-repairing, composite material consisting of a tungsten thin film matrix inside bulk polycrystalline boron-doped diamond from chemical vapour deposition (CVD).

Technical Context
ITER divertor plasma facing components (PFCs) are engineered to withstand 10 MW m-2 of steady-state surface heating. For comparison, the value is approximately 1 MW m-2 for a spacecraft heat shield during re-entry, 10-80 MW m-2 for an arc welder, and 50-150 MW m-2 for a cryogenically cooled rocket engine nozzle.

For the last 25 years, progress in fusion has largely relied on the use of fine grain graphite and carbon fiber composites in the high heat-flux regions, where the carbon technology was adapted from the fission and aerospace industries. More recently, the carbon surface has been enhanced with high performance tungsten thin films (10-200 microns) in order to increase erosion resistance.

Over a similar timeframe, diamond from CVD has become readily available. A CCFE led research programme from 2007-2010 included: (i) a 5 mm thick boron-doped plate prototype exposed to high heat-flux electron beam testing (Figure 1), and (ii) thin films exposed to plasma in several fusion devices.

This is of interest because diamond has many relevant properties that are often best-in-class compared to all other materials:

  • isotropic thermal conductivity 5 times higher than copper at room temperature,
  • very low thermal expansion,
  • the above combine to give diamond unparalleled thermal shock resistance,
  • sublimates instead of melting, low chemical reactivity with hydrogen in a gas environment,
  • forms strong carbide chemical bonds with many metals, including tungsten, high tensile strength, and
  • good resistance to neutron radiation damage.

Objective
The goal is to incorporate layers of tungsten films throughout a boron-doped diamond plate. The intended benefits are:

  • reduce chemical reactivity,
  • increase the erosion resistance to physical sputtering,
  • marginal improved ductility at elevated temperatures, and
  • quasi-self-repairing, since the diamond erodes until a new tungsten layer if the surface film is lost.

If the films are thin enough (< 10 microns approximately), then the bulk properties of the composite should be similar to diamond.

Doping the diamond with boron increases the electrical conductivity without dramatically altering the bulk properties.

This project will aim to produce such a material and test it under fusion relevant conditions.

The project will mainly be based at Manchester but will work closely with UKAEA . There may also be opportunities to collaborate with other labs to carry out high heat flux/plasma testing of the novel materials.

This project is offered by The University of Manchester. For further information please contact: Aneeqa.khan@manchester.ac.uk

This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.

Figure 1: 5mm thick boron-doped CVD diamond.