Physicists reported recently that they have successfully used the lasers built for fusion reactions at the National Ignition Facilityin Lawrence Livermore National Laboratory to compress a synthetic diamond to pressures of 50 million Earth atmospheres (5 terapascals). For the first time scientists measured pressure-density curves of matter at trillion pascal pressures, an extreme environment found in the core of gas giants and super Earth planets.
A tiny sample of synthetic diamond, millimeter-sized and in the shape of a cylinder, was held upright and put into the crosshairs of 176 high powered fusion laser beams. The beams have total peak power of 2200 gigawatts (GW). In comparison, a nuclear power plant only produces as much as energy at a rate of 0.5 to 2 GW. Since power is the energy output over time, the laser beams can only run a very short time at such power, so the total output of energy is not high.
Half the beams are focused on the top half of the cylinder and the other half on the bottom. This squeezes the cylinder when the lasers fire. Upon firing, the physicists measured the rate of diamond material moving under the tremendous heating and counter-reactions. As the cylindrical piece of diamond is compressed, its middle bulges out at extremely high velocities. The measured peak velocity was 109,000 miles per hour, or about 45 kilometers per second.
They found that at the peak pressure of 5 trillion pascals, or equivalently 50 million Earth atmospheres, the density of the diamond had more than tripled. Therefore the diamond was compressed to three times a smaller volume than before, making its density equal to that of lead.
The results were compared to a type of computer simulation called density functional theory (DFT). DFT is based on a branch of physics known as quantum mechanics. While it is an approximate method, meaning that accuracy of representing the underlying physics is sacrificed for purposes of speed, it is quite successful in predicting many complex aspects of matter. The researchers used two types of theories in DFT and showed that the measured results fall right in between the computer predictions.