America's Hottest Lab

A temperature of 2 to 3 billion degrees Kelvin -- hotter than the interior of any known star -- has been achieved in a lab in New Mexico.

The temperature record was set recently in a test shot at the Z Pinch device at Sandia National Laboratory, 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. The process captured in a famous photograph, see Physics News Graphics.

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 (see PNU 702).

Why the implosion process should be so hot, and why it generates X-rays so efficiently (10-15 percent of all electrical energy is turned into soft X-rays), has been a mystery.

Now Malcolm Haines of Imperial College, in London, 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, which is made of 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
Contact Malcolm Haines, m.haines@imperial.ac.uk
Image at Physics News Graphics