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Part 2 of 2 Parts (Please read Part 2 first)
The record plasma generated by the Wendelstein 7-X has now been analyzed in high detail. At high plasma temperatures and low turbulence losses, the usual stellarator magnetic ripple losses in the energy balance could be observed. They accounted for about thirty percent of the heating power, which is a considerable part of the energy balance.
The effects of magnetic optimization of the Wendelstein 7-X can now be shown by a thought experiment. It was assumed that the same plasma values and profiles that led to the record result of the Wendelstein 7-X were also achieved in reactors with a less optimized magnetic field. The magnetic ripple losses that were expect were calculated. They would be greater than the input heating power which is physically impossible. Professor Per Helander is the head of the Stellarator Theory Division at IPP. He said that “This shows that the plasma profiles observed in Wendelstein 7-X are only conceivable in magnetic fields with low magnetic ripple losses. Conversely, this proves that optimizing the Wendelstein magnetic field successfully lowered the magnetic ripple losses.”
However, the plasma discharges in the Wendelstein 7-X have been very short so far. To test the performance of the Wendelstein design in continuous action, a water-cooled wall cladding is being installed. Equipped with this new cooling system, the researchers will gradually extend the plasma time up to thirty minutes. Then it will be possible to check whether the Wendelstein 7-X can also fulfill its optimization goals in continuous operation.
The aim of fusion research is to develop a climate and environmentally friendly power plant. Similar to the sun, the intent is to generate energy from the fusion of light atomic nuclei. Because the fusion reaction will only ignite at temperatures above one hundred million degrees, the low-density hydrogen plasma fuel must not come into contract with the cold walls of the containment vessel. Held by magnetic fields, the plasma floats almost contact free inside the vacuum chamber.
The magnetic cage of the Wendelstein 7-X is created by a ring of fifty superconducting magnetic coils. Their special shape is the result of sophisticated computer optimization calculations. With their help, the quality of plasma confinement in a stellarator should be able to reach the level of the competing tokamak-type facilities.
There are dozens of organizations working on the development of viable commercial nuclear fusion power plants. Over twenty private companies are involved in the research. Many different designs are being explored as are many different types of fuels. Tokamaks were invented by Soviet physicists in the 1950s and are the basis of some of the biggest nuclear fusion projects currently underway. Stellarators were actually invented before tokamaks in 1951 by Lyman Spitzer in 1951. Work on tokamaks and stellarators has been carried out for decades with slow progress. Now there is a sort of fusion race and there are many other designs competing with tokamaks and stellarators. Despite their long history, tokamaks and stellarators may wind up being a dead end as other, more recent designs surpass their performance.
Magnetic field configuration for the Wendelstein 7-X fusion reactor.