The objective of IPP is to develop a power plant that, like the sun, derives energy from fusion of atomic nuclei. Its feasibility is to be demonstrated by the ITER (Latin for "the way") international experimental reactor with a fusion power of 500 megawatts. Construction will start next year at Cadarache in France. The aim here is to confine the fuel – an ionised low-density hydrogen gas, a "plasma" – in a magnetic field cage without letting it touch the wall and then heat it to ignition temperatures of over 100 million degrees. One of the major challenges involved is to achieve tolerable interaction between the hot plasma and the wall of the enclosing vessel.
For ITER, however, beryllium and carbon are no longer without problems: Sputtering of these when bombarded with hydrogen is relatively high. The high hydrogen fluxes from the large ITER plasma would therefore cause severe material erosion. Furthermore, hydrogen particles readily accumulate in carbon, and in ITER so also does its radioactive version, tritium, this being highly undesirable for safety reasons. A wall completely clad with tungsten would obviate these problems with light elements: Tungsten affords advantageous thermal properties, low sputtering caused by hydrogen, and no long-term accumulation of tritium. This leaves the critical question how many of the heavy tungsten particles can penetrate to the core of the plasma. Recent estimates for ITER indicate that it may not be more than a few hundred thousandths.Tungsten experiments at IPP
Despite bad experience in other laboratories, IPP started in 1996 to apply tungsten to special areas of the wall otherwise completely clad with carbon tiles. This relied on the differently chosen, ITER-like, i.e. cold plasma edge of ASDEX Upgrade. The positive result prompted a further reduction of carbon. The aim was to check how this affected the plasma and its interaction with the tungsten components. In order not to jeopardise other research objectives, the tungsten surface was only successively enlarged. Reliably determining the particular tungsten concentration amassing in the plasma is not a simple matter, the less so when the emission losses are attributable not only to a single impurity. Once the necessary measuring methods were developed it was found, however, that even an extensive tungsten surface does not unduly affect the plasma of ASDEX Upgrade.
It remains to prove that even complete metal cladding of the vessel is compatible with the favourable plasma states wanted for ITER – such as the high-confinement regime developed at IPP. After the last carbon tiles had been replaced and all surfaces carefully cleaned, experiments were recently resumed with a purely tungsten wall. To ensure clean experimental conditions no resort was made to the otherwise standard pretreatment of the vessel with boron. In order to reduce losses due to impurity radiation, this process serves to coat the wall surfaces with a thin layer of boron by means of a glow discharge in a boron hydrogen gas. However, in ITER or a subsequent power plant this will no longer be possible.
ASDEX Upgrade has therefore also started without boronisation – and was successful: The tungsten concentration is below the critical threshhold and the desired favourable plasma states can be achieved with only slight loss of quality. Further investigation will aim at exactly checking the tungsten compatibility in ITER-relevant plasma states. The decisive issue will be whether permanently "good" high-confinement plasmas can be achieved without boronisation. For this work IPP has about two years – before the decision on the interior wall of ITER is taken.
Isabella Milch | alfa
Smallest transistor worldwide switches current with a single atom in solid electrolyte
17.08.2018 | Karlsruher Institut für Technologie (KIT)
Protecting the power grid: Advanced plasma switch for more efficient transmission
17.08.2018 | DOE/Princeton Plasma Physics Laboratory
There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.
The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...
New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference
Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
17.08.2018 | Event News
08.08.2018 | Event News
27.07.2018 | Event News
20.08.2018 | Information Technology
20.08.2018 | Life Sciences
20.08.2018 | Information Technology