By Josh Perry, Editor
Researchers from Rice University (Houston, Texas) completed 20 years of study by developing the first laser-cooled neutral plasma, which involves cooling clouds of expanding plasma to temperatures 50 times colder than deep space.
Rice University physicists reported the first laser-cooled neutral plasma, a breakthrough that could lead to simulators for exotic states of matter that occur at the center of Jupiter or white dwarf stars. (Brandon Martin/Rice University)
This new breakthrough, according to a report from the school, enables the creation of simulators that can produce exotic states of matter like those found in other planets or white dwarf stars. While the researchers admit there is no immediate practical benefit to this experiment, new techniques for laser-cooling plasma opens new avenues for study.
In the experiment, scientists used 10 lasers with different wavelengths. They started by vaporizing strontium metal and using a set of beams to trap and cool strontium atoms. The gas was then ionized using a 10-nanosecond pulse from the laser, stripping one electron from each atom to form a plasma of ions and electrons.
“Energy from the ionizing blast causes the newly formed plasma to expand rapidly and dissipate in less than one thousandth of a second,” the report noted. “This week’s key finding is that the expanding ions can be cooled with another set of lasers after the plasma is created.”
The ions are positively charged and repel each other, but the effect of kinetic energy, in the form of heat, is much stronger. In the intense gravity on Jupiter or white dwarf stars, the ions are pushed tightly together and the repulsive forces become stronger and force ions to couple. By lowering the temperature, researchers were able to mimic this.
The research was recently published in Science. The abstract read:
“Laser cooling of a neutral plasma is a challenging task because of the high temperatures typically associated with the plasma state. By using an ultracold neutral plasma created by photoionization of an ultracold atomic gas, we avoid this obstacle and demonstrate laser cooling of ions in a neutral plasma.
“After 135 microseconds of cooling, we observed a reduction in ion temperature by up to a factor of four, with the temperature reaching as low as 50(4) millikelvin. This pushes laboratory studies of neutral plasmas deeper into the strongly coupled regime, beyond the limits of validity of current kinetic theories for calculating transport properties.
“The same optical forces also retard the plasma expansion, opening avenues for neutral-plasma confinement and manipulation.”
Learn more in the video below: