Yukihiro Kusano has conducted research into plasma for 40 years and is one of the few researchers in Denmark trying to find new plasma applications. Photo: Joachim Rode

New doctorate will disseminate plasma technology

Monday 15 Apr 19

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Yukihiro Kusano
Senior Scientist
DTU Wind Energy
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Senior Researcher Yukihiro Kusano has collated many years’ research in a doctoral dissertation. Here he points to new applications of plasma technology—among other things in wind turbine blade production.

Plasma is a well-known physical phenomenon. Lightning, the Northern Lights, and the Sun’s gases are all forms of plasma. And as children, many of us have played with plasma spheres where violet blue lightning moves towards the surface when you place fingers on the glass. Plasma also has many everyday applications: neon tubes, low-energy light bulbs, and plasma displays to name just a few.

Senior Researcher Yukihiro Kusano from DTU Wind Energy is one of the few researchers in Denmark who is trying to find new applications for plasma. His many years of research have now resulted in a doctoral dissertation entitled ‘Atmospheric Pressure Plasmas for Polymer Surface Modification – Alternating Current Gliding Arcs and Ultrasound Enhanced Plasmas’.

Plasma is an ionized gas—i.e. a gas whose components—electrons among others—are separated from the atoms. A plasma state can be created with the help of heat or a strong electromagnetic field. The state can be used for surface treatment, which is precisely the focus of Yukihiro Kusano’s research. Bombarding a material with plasma can, for example, replace the need for the mechanical sanding of the polymer layers that are glued together to make a wind turbine blade.

Doctorate without master’s degree
After completing his bachelor’s degree in Japan, Yukihiro Kusano got a job with car tyre manufacturer Bridgestone in a laboratory conducting research into how to glue surfaces together using plasma.

"When we add ultrasound, we can achieve an even smoother processing of the material. This is especially true when we use the plasma, which is generated at low current. It was a very surprising result, which paves the way for new applications of plasma technology—e.g. in the treatment of our bodies."
Yukihiro Kusano

At a certain point in his career, Yukihiro was offered the chance to take a PhD at Cambridge University, despite not having a master’s degree. Cambridge, however, assessed that his more than 60 patents were sufficient qualification.

After finishing his PhD, he returned to Bridgestone, subsequently receiving an offer from his former supervisor to take part in a major EU project. He accepted, breaking with the then age-old Japanese tradition of working for the same company for an entire lifetime. Despite the changes, however, plasma research has remained the focus of his 40-year career.

In 2003, he had the opportunity to move to Risø where, among other things, he worked with plasma-assisted removal of NOx (nitrogen) from power stations. With a contact in the wind industry, he saw the potential of using plasma to improve the surfaces of the polymers which are glued together to make wind turbine blades. Improved surface means even greater strength in the areas where the parts are glued together.

Due to blade size, it is not possible to work with plasma in a vacuum chamber, which is otherwise often the case. This set the course for much of the research that Yukihiro Kusano describes in his dissertation—working with plasma at atmospheric pressure.

Hotter than the Sun
“The method, I describe (gliding arc, ed.), has actually been around for over 100 years and has also been used before. But the challenge is how to create the optimum surface of a polymer that is to be glued together with another so it can withstand extreme forces. This requires extremely accurate use of the plasma. We use electrical power, but that means that the gas becomes very hot. Up to 6,000 degrees Celsius—just like the Sun’s surface. It can melt anything,” says Yukihiro Kusano.

The electrons in the gas are actually even hotter—up to 10,000 degrees. They have enough energy to change the surface of a material, but because they virtually weigh nothing, they can not penetrate. In other words, there is a need for high electron temperature and low gas temperature at the same time. This is achieved by blowing air between the electrodes. The trick is to hit the point where the gas temperature is low enough to do no harm—a few thousand degrees—while maximum electron energy is preserved.

Plasma treatment can occasionally damage the polymer surface and create a scorched spot. Yukihiro Kusano has found a way to avoid many of these incidental flaws. The trick is to add ultrasound to the process. Ultrasound has the effect that it removes the very thin layer of gas which is naturally present on the surface of the material.

“When we add ultrasound, we can achieve an even smoother processing of the material. This is especially true when we use the plasma, which is generated at low current. It was a very surprising result, which paves the way for new applications of plasma technology—e.g. in the treatment of our bodies, where we cannot use strong currents,” he says, adding that, it can be used in medical treatment, for example, and that this is an area of research experiencing international growth.
Yukihiro Kusano defended his doctoral dissertation on 12 April.

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20 JULY 2019