Helium and Impurity Transport (HIT)
The HIT group investigates the behavior of helium and other impurities in fusion plasmas, with the ultimate goal of understanding how they can impact the performance of future fusion reactors.
Helium is a product of the deuterium-tritium fusion reaction, which is the most promising reaction for energy production. As such, it is an inherent part of the fusion process. The fusion born α-particles transfer their energy to the plasma via collisions, providing the self-heating of the plasma. However, once they have done so, the thermalised helium ions, known as helium “ash”, must be removed from the plasma as soon as possible, to avoid diluting the fusion fuel.
Apart from helium, a fusion plasma inevitably contains other impurities, which can originate from plasma-wall interactions or be intentionally introduced to manage heat loads on plasma-facing components. To achieve a burning plasma, it is essential to understand the transport of the impurities inside the plasma and to control the impurity content.
Our research aims to understand how impurities behave in a fusion plasma and to provide a comprehensive picture of helium from its birth in fusion reactions to its removal from the system. Ultimately, we seek to provide sufficient information to reliably include the helium behavior in the operational scenario development and make reliable predictions for future fusion devices.
The main focus areas of the group are:
Impurity measurements:
We operate several diagnostics to provide impurity measurements in ASDEX Upgrade. Charge eXchange Recombination Spectroscopy (CXRS) is a key diagnostic that can measure the ion temperature, plasma rotation and also the densities of light impurities such as helium in the plasma. Optical Penning gauges are used to measure the helium partial pressure in the divertor and pumping regions.
Helium and impurity transport:
We design and perform dedicated experiments in ASDEX Upgrade to understand the transport of helium and other impurities from the core to the edge of the plasma and to validate the theoretical predictions.
Fast ion studies:
We study the behaviour of fast ions in ASDEX Upgrade, both deuterium and helium fast ions, to learn as much as possible about fusion-born α-particles and other energetic ions. Fast Ion Dα (FIDA) spectroscopy and Charge eXchange Recombination Spectroscopy (CXRS) are used for this purpose.
Helium exhaust:
We investigate how helium is transported from the plasma toward the divertor, to be removed with an appropriate pumping system, in several plasma scenarios in ASDEX Upgrade. Efficient helium removal is crucial in future reactors to maintain a burning plasma and prevent helium dilution of the D-T fusion fuel.