16. PhD Interview

“Nuclear fusion has clearly the potential to provide unlimited amounts of clean (CO2 free) energy.”

Faro Hechenberger, Dissertant an der Universität Innsbruck

What is/was the topic of your Ph.D. thesis?

Reactive low energy ion surface collisions on fusion relevant surfaces focusing on the formation of molecules.

What is/was the focus of research?

Plasma-wall interactions play an important role in any technical and particularly also in fusion plasmas. Erosion of wall material may influence the properties of the core plasma and retention of tritium via chemical bond formation or implantation into the wall represents a major problem for future fusion devices. Preparatory studies with a new instrument indicate efficient formation of beryllium hydride upon irradiation of a Be surface with D2+. Currently our team investigates the molecular mechanism that leads to the formation of BeD+. This product ions are also formed when Ar+ collides with a Be surface that is covered with D2 of sufficiently high density.

In order to facilitate the detection of neutral sputtering products, several major modifications to the instrument are required. My colleague Lorenz Ballauf designed a completely new experimental setup, which is expected to increase the sensitivity by several orders of magnitude. Currently we assemble the instrument and first tests are planned before May 2019. One of the goals of my PhD thesis will be the analysis of neutral sputtering products upon electron ionization and subsequent mass spectrometry. Furthermore, the kinetic energy distribution of both neutral and charged products will be determined via retarding field analysis.

What is/was the benefit for fusion research?

The behavior of surfaces during ion bombardment is an important factor in safety and durability, especially in the inner reactor walls of ITER or other fusion devices. As the magnetic field cannot confine all charged particles in the plasma, ions constantly strike the wall, especially during instabilities and disruptions. So far, the mechanism of ion surface collisions under extreme conditions were mostly simulated. In our experiment, knowledge about retention of hydrogen isotopes and reaction products that may contaminate the core plasma can be acquired. This information is essential for realistic modelling of a fusion device and the choice of appropriate wall materials. The newly built apparatus allows us to characterize reaction pathways leading to complex (molecular) sputtering products. Particularly the investigation of neutral sputtering products is essential, as they can readily pass the plasma sheath and enter the core plasma.

What are/were the biggest challenges?

Building a new experiment is always challenging. Even with meticulous planning, mistakes may occur. Exactly then, strategic and problem-solving-oriented action is necessary. We have designed the new setup to achieve shorter measurement times and better signal to noise ratios by increasing the ion yield. At the same time, this leads to a better understanding of the conditions in the ITER experiments with respect to ion surface collisions. It was also necessary to develop a new ion source that can deliver a higher ion flux. With the development of a plasma ion source, new insights into the interaction of plasmas and supersonic flows have emerged. The further steps in constructing the experiment are the assembly, the connection to the software, the characterization of the plasma ion source and the first tests of the time of flight instrument. So, there are still some challenges to overcome.

Which plans do you have for your future? What will you do in 5 years? Would you like to continue research or are you going to work in industry?

Jobs in academia are very limited but research in industry can also be great. The problem-oriented and structured work I had to learn with the development of this new experiment is the perfect training for research and development in the industry. As a trained teacher, I also like to explain complex issues to students. Such a perfect job for me in industry should also contain some teaching to colleagues or customers.

What was your motivation to write a fusion relevant Ph.D. thesis? What is fascinating about nuclear fusion?

The increasing demand on energy of humankind and the problems arising with fossil fuels asks for alternatives. Nuclear fusion has clearly the potential to provide unlimited amounts of clean (CO2 free) energy. The technical problems that have to be overcome are fascinating and challenging. I hope that in my PhD I can contribute to this major project. At the same time, I can learn techniques and methods that go way beyond the skills of a master student.