Interviewer(INT): Today we will speak to one of the scientists taking part in this KSTAR project. Prof. Na Yong-Su at Seoul Nation University Department of Nuclear Engineering.
Great to have you with us Prof. Na.

Prof. Na (Na): Good Morning!

INT: First of all, could you briefly introduce yourself to our listeners.

Na: It is, indeed, my great pleasure to talk about nuclear fusion and KSTAR with you in this outstanding program. I’m Yong-Su Na from Department of Nuclear Engineering at Seoul National University. I have been working on nuclear fusion since 1998. So it’s about 20 years now. My first study was control of KSTAR tokamak plasmas in 1998 during my Master’s course. After I received Master’s degree, I continued my study in Max Plank Institute and Technical University of Munich in Germany for my Ph. D. I received the Ph. D degree in nuclear fusion in 2003 and started working in Seoul National University in 2008.

INT: Hmm, so you have long resume there. (laughs) When you think about nuclear engineering the first impression that many of us have is it’s difficult to understand and complicated science. Please make it easy for us in layman’s term to start with: What is nuclear fusion?

Na: Okay, I will try to explain as easy as possible. Nuclear fusion is the origin of star energy or sun energy. Mankind was very curious about the huge amount of sun’s energy for a long time. The origin was discovered in the beginning of the 20^th century. And it was nuclear fusion. If 2 light nuclei meet at very high temperature, they can be combined to form another atomic nucleus. For example, 2 hydrogens, you know hydrogen is the lightest element in the universe can form helium by nuclear fusion reaction. This is the process happening in the sun. While two hydrogens make a fusion reaction, the mass of hydrogen is reduced, and the amount of mass reduction is transformed into energy by the famous Einstein law: E=mc2.

INT: Ah… (epiphany)

Na: Where E is the energy, m is the mass, and c is the speed of light. Since the speed of light is very large, huge amount of energy can be released even with the tiny change of the hydrogen mass.

INT: Then, why is KSTAR called an artificial sun?

Na: Okay, KSTAR is a tokamak device, to make and confine an artificial sun to have a nuclear fusion reaction. The hot sun particles so called plasmas, (we say plasma is the fourth state of matter), react against the magnetic field. So in other words they gyrate along the magnetic field lines. KSTAR has strong magnets to produce strong magnetic field to confine some particles plasma particles. Therefore, we say KSTAR is an artificial sun.

INT: So we all know that the real sun is up in the sky, but where is KSTAR?

Na: KSTAR is located in Daejeon. So it was constructed and is being operated by National Fusion Research Institute in Daejeon. It is very close to KAIST.

INT: Right, right. Then, as I mentioned earlier, your team was successful in sustaining fusion temperatures of KSTAR at about 100 million degrees Celsius for 1.5 second I believe. How big of a deal is this? Could you explain the significance of this?

Na: Yes, it is a significant achievement, I would say. To have a fusion reaction, we need high temperature. As you know, hydrogen atom is composed of electrically positive nucleus and electrically negative electron. So it is globally electrically neutral. But for nuclear fusion reaction, two hydrogen nuclei should meet together. The problem is that both are electrically positive, so they push each other due to the repulsive for between them. But if temperature is high enough, they can overcome this repulsive force and can be combined. For the fusion reactions to occur, the plasma temperature should be high enough about 100 million degrees. KSTAR has achieved this 100 million degree for the first time in tokamaks with superconductive magnets.

INT: So to give us, our listeners, a bit of a background. How hot is the real sun? what’s the exact temperature of Sun and why does the temperature of this artificial sun have to be above 100 million degrees?

Na: The temperature of the Sun’s core is about 16 million degrees. So 6 times lower than the KSTAR core plasma. The Sun is much bigger than KSTAR.,10^8 in diameter. So much more plasma particles confined in the sun compared with KSTAR. So the probability of fusion reaction is much much larger in the Sun. To get high fusion power, KSTAR should have higher temperature. So if I use a metaphor, KSTAR plasma is a sports car engine. On the other hand, the sun is a kind of a bus engine.

INT: So higher the temperature higher the fusion power that it creates. And I mean 100 million degrees is just unimaginable. How do you measure the temperature? What kind of special device do you use?

Na: Yeah, this is a good question. It is, it is very interesting to know that we can measure the temperature of the sun and even stars far from our galaxy where we cannot reach. We have experience that the light dispersed according to its wavelength by a prism. So we analyzed the light from the stars, such as the wavelength and its broadening, then we can calculate the temperature of the sun and KSTAR is doing exactly the same as this. We call this diagnostics or measurements spectroscopy.

INT: Professor Na, I understand that KSTAR is already 10 years old. How far has nuclear fusion research in Korea come along so far? And where does it stand as of now compared to other countries?

Na: I would say that KSTAR is the first worldly known fusion device in Korea. In 1979, a tokamak device was constructed in department of nuclear engineering at Seoul National University, so called 79. But it was simply for education of students, a very small device. The KSTAR project was initiated in back to 1995, and its construction was completed in 2007. Since than KSTAR has shown world leading remarkable results: particularly on high performance, long pulse operation, and control of plasma instabilities. Before KSTAR, Korea was invisible country, I would say in terms of fusion research. But after KSTAR construction, Korea has started leading world fusion community.

INT: I want to go back to fundamental question. Why is the artificial sun research so important? I mean the Earth has suffered from global warming. South Korean in particularly is choked with hazardous levels of fine dust recently. Does artificial sun research help in dealing with these environmental problems?

Na: Yes, the fusion uses hydrogen as fuel. So hydrogen can be easily found in H2O, water. So in other words fusion uses sea water to produce electricity, and it does not produce CO2, carbon dioxide, or fine dust during the process. So it produces only a little amount of nuclear waste which can be recycled at least within 100 years. And after the improvement of the technology, we believe that the nuclear waste can be significantly reduced as well. So I can say that fusion an ultimate energy source and a good solution to the global warming and fine dust problems.

INT: It can definitely be an alternative source of energy to solve these many problems. Then how did you first get to join the KSTAR project?

Na: As I introduced earlier, I started graduate course with KSTAR in 1998. After I finished my Ph. D, I joined the KSTAR team at National Fusion Research Institute in 2004 and worked there before I moved to Seoul National University, but I am currently service KSTAR as deputy leader of Advance Operation Scenario Group.

INT: For ordinary people, like me or our listeners, from our perspectives, this project seems to be a tough one. Something that seems almost impossible, but what were some of the biggest difficulties or hurdles in your research?

Na: My research topic is to achieve high temperature and performance and sustainment for long time in stable way. That is highly challenging task indeed. For example, you can reach high temperature as KSTAR obtained 100 million degrees, but to sustain this for 10 seconds is another big challenge. So simultaneous achievement of high temperature, high performance, and long sustainment is very difficult, I would say.

INT: So that would be your next challenge extending that period of time from 1.5 seconds to 10 seconds.

Na: Yes

INT: Okay, and Moon Jae-In administrations pushing to transform the countries power systems switching the main energy sources into renewable ones. And there is a global project called ITER, or International Thermonuclear Experimental Reactor, currently under way for the commercialization of nuclear fusion. And I believe you are serving as a chair of the international experts group on integrated operation scenarios group. Could you tell us more about this project?

Na: Okay, ITER is the world largest fusion program as well as the biggest international research project, where 7 parties are involved. So European Union, including 28 countries, is it now 27 because of U.K. Brexit?

INT: Maybe? (laugh)

Na: Yeah, and the United States, Japan, Russia, China, India and Korea are participating in this project. It is known as the second largest world science program, and you know the first one is ISS International Space Station. And ITER is under construction in Cadarache, southern part of France, very close to Marseille and more than 60 percent of ITER are completed. And the first plasma is foreseen in 2025 and the main goal of this big project ITER is to demonstrate scientific and technological feasibility of fusion power. It aims at producing fusion power 500MW for longer than 400 seconds.

INT: There are so many other questions that I want to ask you, but since we are running out of time, I want to ask you about your future plans for this ongoing research.

Na: Okay, I will work in my effort to achieve high temperature high performance plasmas in long pulse operations in KSTAR. My dream is to contribute to realize fusion energy development. And I will do my best to make this dream come true with students in my group at Seoul National University.

INT: It seems that you are already contributing a great part in this nuclear fusion research in the country. Thank you so much Professor Na for joining us today and sharing your insight with us.

Na: Thank you very much for having me here today