Thursday, 20 September 2012

Nuclear fusion, Not ready yet!

Nuclear power seems like a answer to our prayers when you think how a small piece of abundant matter can make an enormous amount of energy. The use of uranium 235 and a little know-how, changed the world as we know it. Despite using an old system of pressurized water to transfer heat from the core to the heat exchange and onto turbines to generate the electricity, can be tricky as walking a type rope to be operating within safety parameters. Nuclear reactors past record of safety comes into light when accidents like Chernobyl, Three mile Island and Fukashima are mentioned.
Despite my recommendations for a thorium system, which doesn't over heat causing a radioactive cloud to escape into the atmosphere, there is an alternative clean option. The clean option of Fusion power seems so far away but according to Sandia National Laboratories, their scientists say that magnetically imploded tubes called liners, intended to help produce controlled nuclear fusion at scientific breakeven energies or better, have functioned successfully in preliminary tests. It's a key test of a concept called Magnetized Liner Inertial Fusion (MagLIF),based on magnetic fields and laser pre-heating. In the dry-run experiments, cylindrical beryllium liners remained reasonably intact as they were imploded by the huge magnetic field of Sandia's Z machine, the world's most powerful pulsed-power accelerator.
The experimental results - the degree to which the imploding liner maintained its cylindrical integrity throughout its implosion - were consistent with results from earlier Sandia computer simulations, says lead researcher Ryan McBride. These predicted MagLIF will exceed scientific break-even.

Simulations have shown that an accelerator generating 60 million amperes or more could reach high-gain fusion conditions, where the fusion energy released exceeds the energy supplied to the fuel by more than 1,000 times. The liner is intended to contain fusion fuel and push it together in nanoseconds. However, the metallic liner doing the compressing is also being eaten away as it conducts the Z machine's enormous electrical current along its outer surface. It begins to vaporize and turn into plasma, in much the same way as a car fuse vaporizes when a short circuit sends too much current through it.

"The question is, can we start off with a thick enough tube such that we can complete the implosion and burn the fusion fuel before the instability eats its way completely through the liner wall?" says McBride. While a thicker tube would be more robust, the implosion would be less efficient because Z would have to accelerate more liner mass. A thinner tube could be accelerated to a much higher implosion velocity, but then the instability would rip the liner to shreds.
"Our experiments were designed to test a sweet spot predicted by the simulations where a sufficiently robust liner could implode with a sufficiently high velocity," says Mcbride. Next year, the team plans to take the next step of integrating in the new magnetic field and laser preheat capabilities that will be required to test the full concept.
Another promising fusion adventure is the ITER experimental reactor,Site preparation has begun in Cadarache, France and procurement of large components has started. The ITER fusion reactor itself has been designed to produce 500 megawatts of output power for 50 megawatts of input power, or ten times the amount of energy put in. The machine is expected to demonstrate the principle of producing more energy from the fusion process than is used to initiate it, something that has not yet been achieved with previous fusion reactors. Construction of the facility began in 2007, and the first plasma is expected to be produced in 2019.
In a recent keynote address, Stefano Concezzi, director of National Instruments explains the internationally involved project will build a large donut shape reactor, he mentions that the magnetic containment will be able maintain a toroidal shape for plasma containment. Plasma can not remain stable if it touches the outer walls, the Joint European Torus claims that the experimental reactor produced 16 megawatts of power. As well as containment the new ITER reactor will be utilizing a Grad–Shafranov equation that will factor in the outer flux to detect if the inner magnetic field is at equilibrium conditions. The system will be able to correct itself and maintain the proper shape every millisecond. Todays modern super computer can now take the readings compare the data on a look up table and approximating the shape back in the MIMO (multi in multi out) controller back into the plasma containment coils (possibly  by control coils at the perimeter). The small demonstration was a simulated computer view of how the plasma will be permanently remain in the middle. This reacting technology was said to be useful for weather forecasting or earthquake, though it wasn't apparent to me.

The technology to raise plasma temperature to a workable 150 million degrees Celsius has been achieved, and now the potential to maintain magnetic stability may well be reachable. Knowing that magnetic containment can finally be reliable, my views on nuclear fusion has changed and that I feel confident on the future of nuclear fusion. Despite the next experimental reactor that will be incorporating this new technology, 2019 is a long time to wait and see if this self correcting idea will work. But from past attempts with fusion reactors and the grown sophistication of computing power, it seems fitting that fusion technology will be ready in seven years time. There is still other problems yet to be solved, one main hinderance is the reactor inner walls need to be changed ever 5 years or so. Due to the abundance of neutrons, which has a destructive reaction when passing through the walls of the Reactor. Hopefully in seven years the International Thermonuclear Experimental Reactor can finally work out the bugs, and we can move on...

1 comment: