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 20th
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
