Data from Sandia’s high-energy-density water studies add to the body of knowledge about the electronic properties of water, a prerequisite for correctly describing the physics of various objects such as giant planets and shock waves in water
Sandia researchers began work in the high-energy-density water arena to better understand the short-lived, high-temperature, high-pressure fluid environment inside Sandia’s Z machine. The Z machine, which is the size of a major college basketball arena, is the highest peak-current pulsed-power device in the world.
The Z machine is used for studying the physics of nuclear weapons and for learning about fusion reactions that may someday produce commercial power.
Earlier work predicted that water would transition to a state where it would behave like a metallic fluid at 7,000 Kelvin and 250 gigapascals of pressure. The new findings place the temperatures and pressures significantly lower — at 4,000 K and 100 GPa. The new work also shows, unexpectedly, that on a pressure-vs-temperature phase diagram, the conducting, or metallic, phase of water directly borders the superionic phase of water. This is a phase where the water molecule’s two hydrogen atoms are free to move about while the oxygen atoms remain frozen in place.
One ramification of the work by researchers Thomas Mattsson and Mike Desjarlais is a revision of astronomy calculations of the strength of the magnetic cores of gas-giant planets, like Neptune. Because the planet’s temperatures and pressures lie partly in the revised sector, electrically conducting water probably contributes to Neptune’s magnetic field.
In the current year, Sandia’s Z accelerator is undergoing an extensive renovation that will increase the machine’s pulse from 20 to 26 million amps — a 30 percent rise. The question to researchers: How will water behave, subjected to these more extreme conditions?
The effort thus began with a look at a specific problem. “We were trying to understand conditions at Z,” said Mattsson, a theoretical physicist, “but the problems are so advanced that they linked to other branches of science.”
For more information:
Thomas R. Mattsson, Ph.D., 505-844-9215, trmatts@sandia.gov