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“Physics is my hobby”

Prof. Toshiki Tajima is known as the inventor of laser electron acceleration. He is a brilliant theoretician covering a very broad range from fundamental physics to plasma physics. The Munich-Centre for Advanced Photonics is very proud to have attracted him as a guest professor at the Ludwig-Maximilians-Universität (LMU) in 2008. From October 2010 he will be a regular professor at the LMU. Here he talks about mathematics, physics, and where he has his best ideas.

Prof. Tajima, you were born in Japan, studied physics at the University of Tokyo, and left Japan right after reaching your master degree. What was the reason for leaving your home country?

Well, at that time I had a supervising professor, Prof. Ichimaru, who came back from a long research stay in US such as at the Institute for Advanced Study at Princeton. I was quite impressed by his very vigorous science and wanted to emulate his career. The United States promised to keep ready research possibilities and exciting science. Of course going to the United States was a kind of adventure, and in 1973 I was young and tried to find my way.

So you had the same reasons as young people today have?

Yes, exactly the same ones.

You stayed a really long period in the United States and returned not until 2002 as Director General of the Kansai Photon Science Institute to Japan. Are you more American or Japanese?

Culturally, I would say I am more Japanese; I grew up in Japan, got my nearly complete education there and was of course strongly influenced by the Japanese culture. Professionally, I am American; except for the last several years I spent my whole professional life and career in the States.

Prof. Tajima, could you tell us something about your family background?

My family is not a very big one; I do not have many relatives. We were three brothers at home and my father worked in a bank, mother passed away earlier.

So, according to your description, science and specially physics, was not a tradition in your family. How did you discover science and decided to study physics?

When I was a young boy of eight or ten years, my parents subscribed to a science magazine for children. I found it very interesting and liked physics and mathematics best. At the college I decided to study mathematics and physics. After a short time I had to recognize that I am not good enough as a mathematician, but physics was natural to me. It is not a labor but fun; physics is among my best hobbies.

What was your favorite subject at the beginning of your career as a physicist?

The first interesting subject to me was plasma, because it differs from all other matter. If you have solid materials, liquids or gases you may deal it with the means of classical physics: you separate them in single particles and answer your questions by regarding these parts. This will not work in plasma because in this media all parts are connected to each other. Controlling of plasma is very difficult: If you disturb it on one point, the disturbance propagates far beyond and ends in a collective motion, which is very, very hard to work with. Plasma is like a bunch of unruly mob. I found a secret how to let them well behave. My vision was: How can I use its own property to withhold this unruliness of the plasma? And it fascinates me till today: if properly done, plasma is capable to collectively move particles and thus to start up nice and robust movements. In my talks and lessons I often use as an example the image of a pyramid, of which I was fascinated as a boy. The single parts were too big for a person to move, but the collective work of many well-behaving people resulted in a movement of these huge parts into a pyramid.

Science is not a job from nine to five. Many good ideas were generated while taking a shower or driving a car. Where do you have your best ideas?

In the late evening! In the morning I need one or two hours and as many cups of tea to put my dead brain into operation. Then it gets less dead through the day and in the late evening it works best. When I was a student I always had paper and pencil beside my bed to make a note of my thoughts. Today my memory has a kind of framework so I hold my idea hung in my mind.

Thank you very much for the interview!

Interview: Christine Kortenbruck
Photos: Thorsten Naeser