Thursday August 07, 2008 Plasma Seminar
Last Friday I gave a talk to some plasma physicists about the scrape-off layer (SOL), and it went very well. My seminar lasted an hour, and they asked many questions. It was like I was defending my research. I couldn’t answer some questions because most of what I know about the SOL and plasma physics I learned this summer. This experience was my first taste of what is to come in my professional career. Seminars, like the one I gave, are very commonplace in a research driven environment. Ideas are presented and debated among other scientists on a regular basis. It is a very exciting atmosphere for me, and I am excited to pursue science even more.In November the Department of Energy (DOE) will be sending me to Dallas, Texas to present my research at the American Physical Society – Division of Plasma Science (APS-DPS) meeting. This meeting will comprise plasma and fusion research being done all over the US, presented by top researchers in the field. I can’t wait to see what exciting new research is being done. This internship has definitely been the most worthwhile endeavor in my undergraduate career.
This past weekend I met up with my girlfriend and dad in Washington, DC to get away from Princeton for a while. We went to the Newseum, a museum about the history of journalism in the US. The Newseum, is probably one of my favorite museums now. I recommend it. The trip to DC was fun, but it makes me even more anxious to come back home. I’ve got a poster to make, a paper to write, and I’ve got to chop up my 1 hour presentation to 10 minutes so I can give the summary talk to my peers on the last day. I’ll be busy until the last day, August 15... my birthday. Then I have 4 days to rest, and then it’s back into full time student mode.
Posted by jlbarton ( Aug 07 2008, 10:00:23 AM EDT ) Permalink Comments [0]
Friday July 11, 2008 Fruit
Research has been excellent this week. Not only the bugs in my code have been fixed but also my model has shown physical results very close to observed data. Solving non-linear equations with computers has been a unique learning experience to me, but the physics of this model will help us all understand more about the plasma scrape off layer. This computational model certainly has promise, especially for optimizing real tokamak settings. In fact, my mentor wants me to plan to give the plasma physicists at PPPL a one hour seminar on my findings! As an intern, I'm required to give the other interns, my peers, a 10 minute talk at the end of the summer - but a one hour seminar to professional plasma scientists?! This summer could really turn out to be an interesting one.
I'm posting some pictures on here to help you all get a feel for what fusion devices, like the NSTX (National Spherical Torus Experiment) etc., look like.
Below is a cartoon depticting the collision needed in magnetically confined fusion.
This is outside of NSTX, the large tokamak now being used at PPPL. (Taken from www.pppl.gov)
This is the inside of NSTX. Plasma flows are shaped like a fat doughnut, swirling around in here. (Taken from www.pppl.gov)
Monday July 07, 2008 Immersed in Science
Wow. Lots of exciting things have happened within these past couple of weeks. I'm now pretty much deep into my research and learning so much. Two weeks ago, the set of Transformers 2 was on Princeton's campus. I may be in the background with some extras in the movie, so it's worth watching when it comes out.
I'm making many friends, many of whom, are into plasmas (what-a-ya know!). I'm really getting a professional experience being immersed in this culture of people motivated for a similar goal in science. We often discuss our research and suggest to each other how to approach different problems in various ways, often arguing. But this arguing is good. Holding your own in an argument shows that you really understand a topic. I'm keeping a journal of my research progress as well as papers/books I am reading. I will post some of this material soon. I also sat in on a research group meeting for NSTX. It was very interesting to see how the 'pros' work out real problems and present their individual findings.
I went to Philadelphia for the fourth of July. (What a dirty city!) I saw fireworks and went to the Institute of Natural History museum, University of Pennsylvania's Museum of Anthropology and Archeology, and the Pennsylvania Zoo. The zoo had vampire bats, which makes sense that they would come to a “sylvania”. I also had a real cheese steak. I don't know why I can't eat those every meal. Maybe it's because I felt like I was shot by a tranquilizer dart after I ate it. But it was good none the less.
Monday June 16, 2008 Getting Started
Today was training day for new PPPL employees. So that meant going through safety lectures and taking multiple tests, sexual harassment and work hazard videos, as well as many, many forms to fill out. It wasn't that bad, but I've never had to go through that much to start a job. I'm not complaining. I'm working in an area where they get matter that's hotter than the core of the sun, so sure, it's hazardous.
I also “got badged” as they say. That phrase was pretty much the joke of the day. How often do you take a noun and turn it into an intuitive verb and no one notice? Like right now, I'm “blogging”. But for some nouns it doesn't work. Like you can't go “carring”: you drive your car. Or you can't get some “booking” done. You get the idea. So anyway, I have a security badge for the PPPL, and it's pretty sweet.
I'm an official PPPL researcher now. It's time to get started.
Posted by jlbarton ( Jun 16 2008, 09:09:29 PM EDT ) Permalink Comments [2]
Saturday June 14, 2008 Day 4 and 5 of 5: Plasma Crash Course
These past two days have been pretty routine. Thursday and Friday comprised our last days of intensive plasma physics lectures and free food. I'm pretty much used to the heat now too. The leftovers will probably be demolished by Sunday night, then we must fend for ourselves like “responsible adults”.
I got a chance to talk to some Princeton graduate students these past couple of days. It's really interesting to find out what they're researching and how life is as a poor grad student. One grad student, originally from Arizona State University, compared life here to his “party school” undergraduate days. He said that the culture here is so much different due to its atmosphere of intelligence. You can always find yourself in an intellectual conversation because everyone here is seeking a learning experience. The best minds in the world come here to study, so you can't help but become a better student in whatever discipline you desire. The analogy I think of is like going to Micheal Jordan's house to learn to play basketball or studying Roman history in Rome: this is the place to learn physics. The motivation one gets here is comparable to nothing else. That being said, I can't wait to dive into my research on Monday.
Here are the summaries of the last 6 lectures of the crash course.
Introduction to ICF – Dan Clark, Lawrence Livermore National Laboratory
Inertial Confinement Fusion (ICF) is the theory that one can use the inertia of the atom's own mass to force nuclei to overcome the nuclear strong force and fuse. Lasers focused around a capsule of cryogenic fuel blow off the capsule and force the fuel implode on itself. The heat from the implosion can rise to thermonuclear conditions for fusion. Ignition occurs when the Strong Force is overcome, and a burn wave propagates out with hot neutrons needed for energy consumption. The laser energy needed to produce this phenomena is being built at Lawrence Livermore, and spans the length and width of three football fields. The precise instrumentation was explained as well as the engineering obstacles that have still not been overcome.
Waves in Plasma – Cynthia K. Phillips, PPPL and Princeton University Dept. of Astrophysical Sciences
This advanced subject was very difficult to grasp, especially coming from an expert who explained every facet of this science without taking a breath. An important attribute of plasma is that electromagnetic waves phase speed is faster than that of light. So the EM wave frequency has special properties. She discussed and derived many important equations as well as how radio frequency waves can be used to heat the plasma.
Plasma Diagnostics – Jill Foley, Nova Photonics, Inc.
Foley discussed the important tools used to gather useful information from the plasma and the physics behind the tool design.
Capsule Physics – Dan Clark, Lawrence Livermore National Laboratory
In ICF, the fuel needed to fuse is first put inside a capsule. The capsule design is so important, that any flaw in the structure will cause any hopes of fusion to disappear. Most of the talk centered around mathematical models of instabilities. Richtmyer-Meshkov, Kelvin-Helmholtz, and Rayleigh-Taylor instabilities were applied to how the capsule ablates and how one could change the capsule design to counter these effects. He argued a case of putting layers of different materials to ramp up densities as the outer layer material's density begins to fall.
Plasma Astrophysics – Michael Brown, Swarthmore College
This was, by far, my favorite lecture of the series. Brown showed how Magnetohydrodynamics and other conservation laws work in astrophysical plasmas. He also showed video clips from the Hinode satellite telescope of the sun's flares and examples of magnetic reconnection.
Phase Space Engineering – Nat Fisch, Princeton University Dept. of Astrophysical Sciences
Fisch presented a way to heat plasma using rf (radio frequency) waves. He explained the apparatus that creates these waves and mathematical strategies to impose the correct frequency inside the plasma. The frequency one needs inside the plasma is reflected outside the plasma, so he must change the frequency on the fly once the wave is inside the plasma. This is a very hot area now in fusion research.
Posted by jlbarton ( Jun 14 2008, 09:14:36 PM EDT ) Permalink Comments [1]
Wednesday June 11, 2008 Day 2 and 3 of 5: Plasma Crash Course
Sorry I didn't post anything yesterday. It's hard to be productive in this sauna-like building. At least last night I only sweated through half the night. The thunderstorm seemed to cool down everything. We did have an interesting dinner last night, however. Since the Princeton dining halls have, for some reason, shut down this week, the Department of Energy has been footing the bill for our recent dinners. They ordered 24 pizzas for 30 people (the NUF and SULI programs combined). And tonight we got tons and tons of pasta. Since the PPPL takes care of our breakfast and lunch, we have more food than we know what to do with at the dorm. Food is always a luxury, no matter how bad we wish for AC.
Today we took a tour of the lab and saw all the major current projects going on. In my experience, I have only seen university standard labs. It's amazing what machines one can build and what progress one can have when the budget is in the billions. I also got to meet my research mentor today. Dr. Rajesh Maingi has three degrees from NC State, believe it or not, and his title reads “Distinguished Researcher”. So naturally we already have some things in common. (Well, maybe someday “distinguished” will be part of my title.) Dr. Maingi showed me where my office, the gym, and, most importantly, the coffee pots were all located. Basically for now I will just be learning IDL (the programming language I will be using) until next week, when the lectures are finished and the real research begins.
Now I will summarize an even more brief version of my notes from yesterday.
Computational Plasma Physics – Bill Dorland, University of Maryland
Dorland showed various slides and animations resulting from simulations attempting to model the turbulence in plasma, whether it be astrophysical or in the NSTX (spherical tokamak). He discussed his method of modeling physical phenomena and some data layering tricks in modeling the plasma flow in toroidal tokamak. What was really interesting was the future in modeling plasma may come from parallelizing video game consoles to make computations even faster. It's amazing how much effort has been put into “blood spattering” physics in video game designs. Now this technology may be used for some really advanced physics!
Magnetic Reconnection – Jan Egedal, MIT
Egedal's talk was mainly on his experiments at MIT on magnetic reconnection: how his device works and what he and his collegues were able to produce. Magnetic reconnection is a phenomena when two antiparallel magnetic field lines are squeezed together until they intersect, causing them to “pinch off”, they separate and reconnect with part of the other field line. Think of when you squeeze the middle of a balloon, except when you squeeze to the middle of the balloon, it seals off both sides and separates.
Z-pinch – Mark Herrmann, Sandia National Laboratories
Z-pinch is mainly an inertial attempt to fusion. They ramp up a magnetic field really high and really fast so that a cylinder of copper wires implodes on itself and the material to be fused. This process would not be a continuous burn of plasma, but rather separate, quick bursts (explosions) of energy. It costs $100,000 each time they want to blow up one tiny piece of fusion material.
Introduction to Plasma – Greg Hammett, PPPL
I don't know why they gave us this lecture so late in the week. It seems like it would make sense to do this lecture first... It was nice to have a review of basic material.
Posted by jlbarton ( Jun 11 2008, 11:51:21 PM EDT ) Permalink Comments [0]
Monday June 09, 2008 Day 1 of 5: Plasma Crash Course
I
have grown a great appreciation for air conditioning. The heat wave
has not held back and my Princeton dorm has no AC. It's no wonder
that Princeton offers no summer courses. But after my first day at
the PPPL, I can already tell this experience will be worth it. Our
first day of intensive plasma physics lectures has begun: O, how one
forgets how hot it is outside when one is trying to understand plasma
dispersion and turbulence...
My favorite quote from today's lectures came from the famous Werner Heisenberg, “When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the first.”
For those who are interested, I am going summarize (very briefly) my notes from today's lectures. This will reinforce the material for me as well as list some high points of plasma and fusion science for those who wish to know more about the subject.
Introduction to Magnetic Fusion – Stewart Zweben, PPPL
Zweben's talk was basically split up into three parts: “The Dream”, “The Reality”, and “The Future”. The Dream is the logic and optimistic outcomes of fusion reaction. You put Deuterium, a naturally occurring isotope of Hydrogen, and Tridium, a radioactive isotope of Hydrogen produced in the reactor from a Lithium “blanket”, nuclei together by making them collide at energies as high as 20 keV (about 200 million degrees C) and you get 17.6 million eV out. Zweben stated, “Deuterium in 1 gallon of water can produce the energy of 300 gallons of gasoline, if burned in a fusion D-T reactor.” Plasma tends to lose energy rapidly and cools down, but if an “ignition” stage is reached, the energy in the plasma will be self-sustained. Ignition is possible, and we have observed it in our Sun and in the H-bomb. The Sun has confined plasma energy over a long time with gravity squeezing its mass tightly at the core. The H-bomb releases its energy all at once, an occurrence no one wishes to observe. Theoretically we can confine the plasma long enough for save ignition in the lab. Plasma ions and electrons helically revolve around magnetic field lines, and scientists have been able to design devices that bend the fields in such a way to keep plasma in a controlled space. Some popular designs are the Tokamak and the Stellarator. If we can confine the plasma long enough for ignition, then we can use the net energy flux of the reactor to heat fluid, exchange that energy to a turbine and generate electricity. In short, this is the most advanced plan ever proposed to boil water.
The Reality is that, “... fusion is facing many serious scientific and engineering problems, and it is not yet clear that we can make a reactor.” The problems arise from the lack of ability to hold the plasma in long enough for ignition at the proper densities and temperatures required. Plasma transport is extremely difficult to understand due to turbulence. Pressure limits, confinement, maintaining steady-state plasma, and plasma-wall interactions are all problems facing a practical reactor.
The Future holds new inovations in plasma science with ITER and other Tokamak designs, better Stellarator designs, and a world wide effort to master magnetic fusion. Computational sciences are hopeful in finding optimum designs without costly experiments. Technological innovations like in superconducting technologies improve experiments. And we also hope for what Zweben calls “physics surprises”.
Magnetohydrodynamics (MHD) – Ben Chandran, University of New Hampshire
Magnetohydrodynamics or MHD takes a fluid modeling approach to understanding plasma. Chandran derived the single fluid equations for MHD and made the assumption of Quasineutrality in the plasma. After seeing how involved this “simple” approach was, I as well as all of the other interns were surprised at how much Chandran could get into a one hour lecture. Quasineutrality is the assumption that the ion and electron densities are approximately the same and so the velocities are approximately the same. What's interesting is that the velocity is a function of both space and time in a fluid. This more complex definition of velocity makes sense if you have ever seen water go down a drain and notice water closer to the drain moves faster. Also, the pressure force in the fluid is simply proportional to the gradient of the pressure. If you have ever gone so deep under water that your ears have “popped”, then you have a first hand experience with this pressure gradient.
Using these special terms of acceleration (from velocity) and pressure combined with the Lorentz force, Chandran showed a relation of plasma current to a magnetic pressure force and a magnetic tension force. The tension force has to do the resistance to pulling the field lines (much like pulling a rubber band). This equation is used to describe the momentum. A magnetic induction equation was derived using Ohm's law with the magnetic term added in.
The Frozen-in Law was discussed and is basically a statement that the plasma “fluid” that is connected by two intersecting flux surfaces remain attached to a field line. So if you have two planes, both of which have magnetic fields pointing in the same direction, the plasma moves with the field lines, but at the line of the two planes' intersections, the plasma attaches to that field line. In fact, the plasma can change that field line due to turbulence making the field stretched and tangled. These changing field lines create low frequency Alfven waves that propagate transversely away from the plasma.
Single Particle Motion – Bill Dorland, University of Maryland
In Dorland's talk, he derived the motion of ions/electrons in a plasma with uniform fields. The helical motion of an ion around a magnetic field (with no E field) can be simply found by setting the Lorentz force equal to the acceleration times mass. The perpendicular velocity divided by the cyclotron frequency is defined to be the Larmor (gyro-) radius. When an electric field is introduced, we changed our frames of reference to get a velocity at which we cannot “see” an electric field. As it turns out, the solutions are similar, but there is now a new term in the velocity that has nothing to with mass, time, or any properties of the plasma: only the E and B fields. This term is called the ExB drift. And from this drift term we found what is called the drift velocity. These drifts result in plasma escaping magnetic field lines and hitting walls in plasma confinement chambers. This problem is hopefully solved in stellarator confinement, which is a twisted magnetic field as opposed to the circular fields in a tokamak. Stellarators hope to average out forces that try to let ions out of parallel and perpendicular confinement.
Turbulence and Transport – Nikolai Gorelenkov, PPPL
We first reviewed some basics on random walks and mean free path theory to get a basic idea of gas transport principles. Diffusion is a problem in plasmas because, like gasses, they want to gain as much entropy as possible. For fusion, we want ions to collide, so diffusion is naturally the enemy. Parallel diffusion (along B field lines) is small due to the confining nature of the field. So perpendicular diffusion is of interest because magnetic field strength is responsible for how much the plasma is allowed to diffuse. But with a stronger field, Coulomb interactions increase turbulence. Eddies in these turbulent flows create changing diffusive gyro radii much like random walks. Gorelenkov showed some linear estimates to the diffusion rate equations and discussed some hopes of computational, theoretical models to help solve the behavior of turbulent flow, especially its internal structures.
Posted by jlbarton ( Jun 09 2008, 08:23:12 PM EDT ) Permalink Comments [0]
Wednesday May 21, 2008 About the Princeton Plasma Physics Laboratory
The PPPL is a Department of Energy Lab overseen by Princeton University. Its main purpose is study fusion and plasma science to make fusion energy an avialable energy source that will rid our dependence on foreign oil and reduce the amount of harmful emissions into the atmosphere. While fusion is a lofty goal, the lab has also made breakthroughs in plasma science that have led to inovations in many fields and applications, including: supercomputer networking, computer chip manufacturning, medical MRIs, plasma tv's, energy saving light bulbs, plasma astrophysics, dynamo theory, space plasma physics ("space weather"), and high energy density physics just to name a few. To see more about the lab and its contributions to fusion science, here is a video from the PPPL website: "Fueling the Future".Posted by jlbarton ( May 21 2008, 06:53:50 PM EDT ) Permalink Comments [1]
Wednesday May 14, 2008 New Weblog Created!
Hello all. This is my new weblog for the summer. I will be periodically updating this page with the new and exciting things I will be doing. Feel free to post comments and questions!Currently I am working with Dr. Blondin in the Physics department here at NC State creating a 3D computational model for self gravitating systems to ultimately understand why stars explode. This has been a semester project that will hopefully produce some fruit before I leave for my internship this summer at the Princeton Plasma Physics Laboratory. More details about the internship will follow soon.
Posted by jlbarton ( May 14 2008, 01:55:31 PM EDT ) Permalink Comments [0]