‘Scrapyard challenge’ to make nuclear fusion more economic

British scientists have begun investigating ways to make nuclear fusion more economic — using research equipment they built from parts of other old machines.

A team from the Culham Centre for Fusion Energy (CCFE) has spent the last two years assembling a device for studying cheaper materials to use with tokamak reactors, in a project the programme leader called a ‘scrapyard challenge’.

The Small Negative Ion Facility (SNIF) will test ways of producing the particle beams needed to heat the plasma inside power-plant-scale reactors, studying alternatives to the highly reactive caesium used by current fusion research projects such as ITER.

‘Caesium makes it easier to produce negative ions but if you try and scale the operation to a power plant you find you’re using 20kg of caesium a year,’ technology programme leader Dr Elizabeth Surrey told The Engineer.

‘Caesium’s not a very nice material. It combusts spontaneously on contact with air, it’s highly reactive and is just not the sort of thing you want to have kilograms of hanging about.’

The researchers will use the SNIF to look for other more easily handled materials that readily give up electrons, such as diamond or lanthanum oxides, and can be used effectively to convert hydrogen atoms into negative ions.

Although the SNIF operates at a much lower energy (30kV) than the machines needed for power-plant reactors would do, its size makes it flexible enough to quickly change the ion source material and easily assess each sample’s success in producing ions.

The new research marks a return to negative-ion research at Culham after more than a decade of focusing solely on positive ions, which are less efficient in the process of heating fusion reactors but are easier to create.

SNIF Project plasma glow discharge: the negative ions produced can heat up fusion reactors

Foreseeing the need for more cost-effective methods to take fusion beyond experimental reactors such as the international ITER project towards commercially viable power plants, Surrey led a small internal programme to build a cheap test-bed that would resurrect negative-ion research at Culham.

Limited to a budget of £180,000 and a part-time team of staff, Surrey was able to source vacuum tanks from a pellet-injector, an ion source and a radio frequency (RF) power supply, all from previous research programmes at the centre.

The biggest challenge was transferring enough power into the vacuum chamber by designing the correct circuits, she said. ‘It’s getting that coupling so the power goes from the RF antenna through the window into the plasma that’s proven very difficult.’

The Culham team has now been operating the machine since June. Jamie Zacks, a lead physicist on SNIF, said in a statement: ‘For the first time in 15 years, CCFE now has its own negative ion test-bed, instead of borrowing facilities from other labs.

‘This, combined with its size, gives us much more control and flexibility over experiments and allows us to open up new collaborations with partners. So far SNIF is performing very well but there is much development still to do.’