Well I've been busy trying to make a start on some basement renovations but I decided to come up for air and to make contact with my poor neglected blog. I just happened to notice the curious image (left) on the main page of wikipedia which led me to today's post. A few days ago, the US national lab in Livermore announced that their National Ignition Facility is now completed, tested and ready to start doing real experiments in inertial confinement fusion.Many years ago, I remember being aware of magnetic confinement experiments using donut-shaped prototype fusion reactors. These "tokamak" reactors with electromagnetic coils wrapped around their donut shape are rather like small versions of particle accelerators, with the fusion fuel forced to circulate around the middle of the donut. Fusion holds the promise of clean energy (just like the Sun's!) since the idea is to use the same nuclear fusion reactions involving isotopes of hydrogen (deuterium and tritium) that occur in the Sun. This, of course, doesn't obviously indicate that the energy production would be clean. Deuterium and tritium combine to form helium innocuously enough. But all the unreacted tritium is radioactive, which has to be taken into account during decommissioning, but its half-life is only 12 years so it doesn't represent a long-term headache. However, the sides of the reactors themselves become radioactive due to exposure to energetic neutrons that are produced along with the helium. Nevertheless, if fusion energy became feasible via magnetic confinement, these radiation concerns are very different from today's nuclear fission reactors that create long-lived radioactive waste in direct proportion to the amount of energy created. The real issue is that no one has managed to get more energy out than they have to put in to keep the deuterium and tritium confined and hot enough to react.
But I am ashamed to admit that I was totally ignorant of the laser approach to the problem of attaining temperatures and pressures equivalent to the interior of the Sun. I feel so out of touch here it's as though I've been hiding in my basement for years not days! This laser inertial confinement method is reminiscent of the H-bomb design, whereby a fission explosion is used to implode the fusion material to create the higher temperature and pressure for the fusion reaction to proceed. Indeed, the number one motivation behind the National Ignition Facility is in fact to continue H-bomb research without doing full-scale tests. They will use 192 extremely powerful lasers which converge on a tiny pellet of fusion fuel inside the target chamber shown in the picture. The final amplified laser energy will give a total power of 500 trillion watts. This is about 1000 times the electrical power that is being used across the whole of the US at any one time, but it is only maintained for a split second. After this the optics get distorted from the heat involved in the light amplification and the system has to cool down for several hours before the lasers can fire again. Ignition is said to occur if more energy comes out than goes in.
Whereas an isolated laser firing performs a valid simulation of an H-bomb detonation, a power station would require a constant stream of fusion fuel pellets to be ignited, so that a continual stream of fusion energy could be made available to convert water into steam to run turbines for electricity generation. France has a similar project called Laser Megajoule expected to be completed next year. A large European High Power laser Energy Research facility (HiPER) aims to focus on more efficient ignition methods by using one laser pulse to provide adequate compression when combined with another laser pulse to heat the compressed fuel to reach ignition conditions.
These big science projects are all very impressive displays of technological prowess, but for many years, the promise of power stations running on nuclear fusion has remained a far-off dream. There's something comical about playing around for years with extremely expensive facilities where you always end up pumping in way more energy than you get out. No wonder we all got excited by the possibility of cold fusion!
7 comments:
i have an concept on photons whom to say
My uncle worked on the magnetic attempts. Me, I don't see fusion close up on the horizon, but it would sure be nice.
Having said that, playing around with expensive facilities that use more power than they produce might just do at least one of these things: find an error that could have made an energy producing facility INTO an H-Bomb or find the key ingredient that's missing on making a viable fusion reactor.
Both approaches to fusion are really important to our future. This work has to go forward. It costs a lot of money but against the kind of funding wasted in the oil business it's just petty cash. Magnetic confinement fusion has already endured a hard 50 years with insufficient funding to take on a technical challenge of immense proportions, yet now they are really getting somewhere, and the international ITER Project (now building in France) is taking the work forward, while perhaps the world's leading magnetic fusion development facility is at Culham in England. Laser fusion research is the new kid on the block, having only been going on for a few years, but one advantage is that it has been able to profit from knowledge and facilities left over from the cold war and the nuclear test ban treaty.... huge lasers are used to verify nuclear stockpiles without having to explode actual weapons. NIF will prove the principle of using a large laser to trigger fusion..., probably in the next 2 or 3 years... then the game really gets interesting, with the international HiPER Project setting up to develop a prototype which will demonstrate how future laser fusion plants can be built, to produce large quantities of grid-level power. Watch this space... Fat-cat bankers screwing up the economy is just a passing phase. The fusion challenge is our real history in the making !
Yeah, I didn't really mean to sound so dismissive. I think it's well worth putting some money and effort into fusion research. I think the scale of the NIF project gets me though - a laser system three football fields in size all focussed on a tiny pellet just seems so bizarre.
I guess when you take the big scale of the Manhatten project and how the scientists managed to solve the technical issues over a tight schedule of only a few years and compare it to the time-scale over which fusion research has been going on, one can only conclude that making a horrendously powerful explosion is a lot easier than developing a controlled, continuous way to extract energy for peaceful purposes.
I have changed locations, by the way.
Rocket Scientist is now at http://Rockets-r-Us.blogspot.com
Ask Me Anything is now at http://askthers.blogspot.com
Take care.
The Braille display developed at SRI is based on activating a type of polymer consisting of a thin sheet of acrylic that deforms in response to voltage applied across the film. The individual Braille dots are defined by a pattern on this film, and each dot is independently activated to produce the dot combinations for Braille letters and numbers.
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