In 2006, scientists at Sandia Labs recorded temperatures of 3.6 billion degrees Fahrenheit, or two billion degrees Kelvin, within a super-heated gas called plasma. The temperatures were reached with the aid of the Z machine, which is an x-ray generator.
The only things in the Solar System that comes close to such an extreme temperature are the center of the Sun, estimated to be 29 million degrees Fahrenheit, and thermonuclear fusion experiments, which are about 500 million degrees Fahrenheit. The Z machine is the biggest x-ray generator on the planet. Exactly how this temperature was reached puzzled the scientists because the amount of energy released after the reaction was far greater than the amount going in.