| Top Stories in General Info |
| IAEA Conference on Fusion Energy | | Date Created: Nov 10, 2004, 08:02 AM |
 A report from the 20th IAEA Conference on Fusion Energy held last week at the small resort town of Vilamoura, Portugal.
My first observation is size. I've been attending these meetings for more 16 years, and the number of participants attending each meeting grows. I don't know the exact count, but there were well over 500 scientists from around the world. The larger numbers of
Europeans and Japanese scientists were particularly noticed. Several meetings encouraging further international collaborations in fusion research were held. With the growing success of the Chinese fusion program (their construction of the superconducting "EAST" tokamak) made interest in stronger Chinese-U.S.
collaboration very welcome. |
 My second observation was the quality of fusion-plasma "imagery". High-speed diagnostics and image processing were everywhere. Movies of plasma dyanamics and of realistic computer simulations of plasma dynamics made a big impression on me. Previously, I could only visualize the complex motion of magnetized plasma in my
mind. I would make line graphs of data measured at localized positions around a torus. Now, I could see the whole thing! Long, stretched-out flux tubes of hot plasma would be accelerated at high-speeds to the vacuum vessel walls of the magnetic containment experiment. These are laboratory equivalents to the coronal loops at the surface of our sun. When the first pictures from the SOHO and TRACE satellites appeared 10 years ago, I remember feeling the same way: it was like a child walking past a toy store, day after day, and finally earning the opportunity to walk inside and see everything with eye's open.
Third observation: the remarkable advancements in high-temperature plasma control tools. RF waves, beams, current-drive, external coils, passive and active feedback. Today's fusion device is covered with actuators. It seemed complicated to me, but it
worked!
Finally, I noted science and basic physics alive and well. Two talks were particularly impressive: Mike Zarnstorff and Stewart Prager. They spoke of quasi-symmetric stellarator and reversed field pinch experiments.
Figure at top: Frame from the neutron tomography images of the Joint European Torus (JET) experiment. Small puffs of tritium were injected at the edge of the plasma, and tomographic movies could trace the particle transport of the fusion fuel. Beautiful. |
| Research Conference (and Fusion Energy Alternatives) | | Date Created: Sep 25, 2004, 09:05 PM |
 Every Friday morning beginning at 9:15 am, the Department of Applied Physics and Applied Mathematics holds its "Research Conference". Here, faculty staff, and graduate students share their research progress, plans, and ideas. It's alot of fun, and one of the events that I most enjoy. This is the time when I can learn about the many new developments, projects, and discoveries made by members of our Department.
This past Friday, the Research Conference began with a talk by Prof. Chris Wiggins about bio-molecular networks associated with gene expression. The talk discussed the mathematical modeling used to understand and predict this very complicated process. Gene expression changes depending upon the cell's chemical environment. This is a fascinating and important area of research.
One comment by Prof. Wiggins was especially relevant to our class. Scientists are making great use of radiation to investigate the biochemistry of genes. Radiation can selectively destroy (or turn off or "knock out") genes, and the effects are now being studied from the point of view of cellular systems biology. The now routine use of DNA micro-array chips has accelerated the pace of this research. |
I was the second speaker, and I spoke about my research specialty in high-temperature plasma physics and fusion energy. I described my laboratory and computational studies of plasma "mixing" in an "artificial radiation belt." I described the world?s effort to build a large $6 billion experiment to investigate the behavior of strong self-heated (or ?burning?) plasma. This device would produce net power at the scale of a possible fusion power plant. Finally, I spoke about a new experiment, the Levitated Dipole Experiment that was completed this past summer at MIT.
During my talk, I had to explain the basic nuclear science of fusion power. Laboratory fusion involves nuclear reactions that release tremendous amounts of energy when light isotopes of hydrogen combine to form helium. A glass of water contains enough deuterium to be the energy equivalent of more than 250 glasses of oil! |
|
To date, fusion power has been generated by the fusion of deuterium with tritium to form an alpha particle and a fast neutron. The cross-section for this fusion reaction is the largest (why?), and this makes it the easiest to produce in the laboratory. However, D-T fusion has two disadvantages. First, the neutron that carries away most of the energy (can you calculate how much?) is highly penetrating. As it passes through the materials that surround the hot plasma, the neutron causes activation. (Fortunately, these materials can be selected to nearly eliminate any long-lived radioactive material.) Secondly, tritium doesn?t exist naturally. With a half-life of about 12 years, it must be created.
The hoped-for plan for D-T fusion energy involves three nuclear reactions, and two of these are fission reactions. The D-T fusion reaction creates a fast neutron. This neutron most often splits a Li-6 nucleus into an alpha particle and a triton. But, we must make certain that there is enough tritium to replace that burned in the fusion reactor. Be-9 is also used in the material near the plasma. When a D-T neutron collides with Be-9, it fissions into two alpha particles and two more neutrons. Be-9 is a neutron multiplier. |
|
The Levitated Dipole Experiment aims at a much more difficult fusion power cycle: one that does not require breeding of tritium. In this scheme, deuterium is combined with other deuterons and with the (natural) light isotope of helium, He-3, to form protons and alpha particles. This fusion cycle only involves fusion. As the reactions above illustrate, tritium is one of the (fusion) products, but if the plasma particles can be made to circulate from the hot core to the colder edge, there's a chance that the tritons can be pumped from the reactor before the create fast neutrons. If the tritium is stored for 12 years, it decays into He-3 (and an electron). The He-3 can then be injected back into the plasma where it can fuse with deutrerium to form He-4 and protons.
This fusion cycle avoids the need to breed tritons and reduces the damage and activation of the surrounding structure by reducing the intensity of neutron radiation. |
| Welcome to my AP4010 Class Blog | | Date Created: Sep 01, 2004, 04:22 PM |
 This is a new idea for me: Create and maintain a web "blog" for our class AP4010 Introduction to Nuclear Science. Today's students and faculty are busy, balancing activities at multiple sites and keeping very full schedules. The idea of a "blog" is to have one on-line location for informal, up-to-date comments about our course, materials, homeworks, comments, answers, and corrections. The blog will not replace class handouts; it will not replace or serve as a substitute for our classroom discussions and lectures; and it will not replace any one-on-one conversations that you may wish to have with me about our course (or anything else about Columbia.)
|
Like other blogs, I intend to write the material with a "first-person" point-of-view. Often, I will give some personal comments about what excites me about our lecture topics. I'll include links to supplemental materials. Since I love the historical context of the development of nuclear physics during the last century, I also intend to include links to relevant biographies, papers, and insights by some very remarkable scientists.
|
Like other blogs, I want to make comments interactive. Interactive class "blogs" are not yet available at Columbia University (although this feature has been discussed!) I am not yet sure whether or not this feature will be helpful or not. For one thing: it is not private! We may get comments from medical physicists and students from around the world. Alternatively, you may email your comments to me mauel@columbia.edu. I'll post your contributions to the blog if two conditions are met: (1) you have to give me permission to share your question with others, and (2) your comments/questions must be judged by me to be relevant or interesting.
|
I'm really looking forward to our first class next week. Until then, best wishes...
|
| Articles in General Info (Total Entries: 10) | | | | | | | | | | |
|
|
|
