Fusion "Breakthrough" at NIF? Uh, Not Really …

As usual the news agencies have run off half cocked screaming "Breakthrough!"....when in reality it was only a small step forward in a long journey that has really just begun....

"One requirement for ignition is that energy output should exceed the energy input from the laser, i.e., that gain (output divided by input) should be greater than 1. NIF's laser input of 1.8 MJ is roughly the same as the kinetic energy of a 2-tonne truck traveling at 160 km/h (100 miles/h). The output of the reaction-14 kJ-is equivalent to the kinetic energy of a baseball traveling at half that speed. Numerically speaking, the gain is 0.0077. The experiment "is a good and necessary step, but there is a long way to go before you have energy for mankind," Campbell says."

"For fusion experiments, NIF directs 192 laser beams from all directions at the fusion target in a pulse that carries 1.8 million joules (MJ) of energy. The outer part of the target is a tiny metal can the size of a pencil eraser, called a hohlraum, at the center of which sits a plastic sphere smaller than a peppercorn containing frozen fusion fuel-a mixture of the hydrogen isotopes deuterium and tritium, known as DT. The ultraviolet beams are fired into the hohlraum through holes at each end but not directly at the fuel capsule. Instead they hit the inner walls of the hohlraum, heating it so much that it emits a pulse of x-rays. The x-rays cause the plastic capsule to explode, driving the fuel inward toward its center.

If all goes according to plan, the fuel-compressed to 100 times the density of lead-will ignite a fusion reaction, but the laser-driven implosion does not provide enough energy to burn all the DT fuel. Some energy from the fusion reactions is needed to keep the burn going. DT fusion reactions produce two products: helium nuclei (aka alpha particles), which carry 20% of the reaction energy as kinetic energy; and neutrons, which carry the rest. For fusion to work as an energy source, the alpha particles must efficiently heat up the fuel to keep the reaction running."

http://news.sciencemag.org/physics/2013/10/fusion-breakthrough-nif-uh-not-really-%E2%80%A6