Tuesday, February 28, 2006

An Ion Temperature of 2 to 3 Billion Kelvin,

hotter than the interior of any known star, has been achieved in New Mexico.  This temperature record was set recently in a test shot at the Z Pinch device at Sandia National Lab where an immense amount of electrical charge is stored in a device called a Marx generator.  Many capacitors in parallel are charged up and then suddenly switched into a series configuration, generating a voltage of 8 million volts (a process captured in a famous photograph). This colossal electrical discharge constitutes a current of 20 million amps passing through a cylindrical array of wires, which implodes.  The imploding material reaches the record high
temperature and also emits a large amount of x-ray energy. Why the implosion process should be so hot and why it generates x rays so efficiently (10-15% of all electrical energy is turned into soft x rays) has been a mystery. Now Malcolm Haines (Imperial College) and his colleagues think they have an explanation. In the hot fireball formed after the jolt of electricity passes through, they believe,
the powerful magnetic field sets in motion a myriad of tiny vortices (through instabilities in the plasma), which in turn are damped out by the viscosity of the plasma (ionized atoms). In the space of only a few nanoseconds, a great deal of magnetic energy is converted into the thermal energy of the plasma. Last but not least, the hot ions transfer much energy to the relatively cool electrons, energy
which is radiated away in the form of x rays. (Haines et al., Physical Review Letters, 24 February 2006)

The American Institute of Physics Bulletin of Physics News
Number 767 February 28, 2006 by Phillip F. Schewe, Ben Stein, and
Davide Castelvecchi

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