"The portable cold atom vacuum standard has passed its first big test," said Eckel. Atmospheric pressure at sea level is around 100,000 Pa. That's about the same as the pressure surrounding the International Space Station. The units were able to accurately measure pressures as low as 40 billionths of a pascal (Pa), the SI unit of pressure, within 2.6 percent.
Free pascal constants series#
In a recent series of experiments, when the scientists connected two pCAVS units to the same chamber, both produced exactly the same measurements within their very small uncertainties. This portable cold-atom vacuum standard (pCAVS)-1.3 liters in volume excluding the laser system-can be readily attached to commercial vacuum chambers a narrow channel connects the chamber interior to the pCAVS core. It does not need calibration because the interaction dynamics between lithium atoms and hydrogen molecules can be calculated exactly from first principles. NIST's system, by contrast, gauges the amount of gas molecules (typically hydrogen) remaining in the vacuum chamber by measuring their effect on a microscopic cluster of trapped lithium atoms cooled to a few thousandths of a degree above absolute zero and illuminated by laser light. And they are not compatible with the new worldwide effort to base the International System of Units (SI) on fundamental, invariant constants and quantum phenomena. These ionization gauges can become unreliable over time and require periodic re-calibration. Today, most commercial and research facilities use conventional high-vacuum sensors based on electrical current detected when rarefied gas molecules in a chamber are ionized (electrically charged) by an electron source.
"The next generations of semiconductor manufacturing, quantum technologies, and particle acceleration-type experiments will all require exquisite vacuum and the ability to measure it accurately," said NIST senior project scientist Stephen Eckel. Precision pressure measurement is of urgent interest to semiconductor fabricators who make their chips layer by layer in vacuum chambers operating at or below one hundred-billionth the pressure of air at sea level and must rigorously control that environment to ensure product quality.
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