First Fusion at the Z machine was announced this week at the April meeting of the American Physical Society in Philadelphia. For the first time, Sandia National Laboratories' Z facility in New Mexico has created a hot dense plasma that produces neutrons associated with nuclear fusion. According to Sandia's Ray Leeper, the neutrons emanate from fusion reactions within a BB-sized deuterium capsule placed within the central target in the Z facility, itself about a third of a football field in diameter. While tokamaks cause fusion reactions to occur by confining plasmas in large magnetic fields, and laser facilities focus intense beams on or around a target, Z applies a huge pulse of electricity (about 12 million joules) with very sophisticated timing. The pulse creates an intense magnetic field which crushes an array of 360 tungsten wires into an ultra-light foam cylinder to produce x rays. Striking the surface of the fuel capsule embedded in the cylinder, the x-ray energy produces a shock wave that compresses deuterium gas within the capsule, fusing enough deuterium to produce neutrons. Sandia researchers measured a yield of approximately 10 billion neutrons, around the expected energy of 2.45 MeV, corresponding to a very modest level of nuclear fusion (about 4 millijoules of energy). The deuterium capsule reached a temperature of about 11.6 million Kelvin and was compressed from a diameter of 2 mm to 160 microns. The whole compression took about 7 nanoseconds. Providing outside commentary, Cornell University's David Hammer said the Sandia group performed pretty much a full set of tests to verify that they had achieved nuclear fusion. The ZR (Z-Refurbished) facility, an upgrade scheduled to go online in 2006, is slated to attempt scaled-up fusion experiments. While the Z approach to fusion is a promising, straightforward, and potentially robust method, researchers caution that they are at the start of a very long road in investigating its feasibility as a fusion power source.

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Clearly they have to improve their ratio of energy ouput - to - energy input by approximately 3 billion-fold. Similar strides have been made by tokamak fusion labs over the last few decades. Another problem to solve is how to make energy production continuous, since the fuel capsule at the z-focus has to be replaced each time it fires.