Happy anniversary, liquid helium
111 years ago, Heike Kamerlingh Onnis liquified helium for the first time, a tour the force that netted him the Nobel prize. It took a laboratory of a size rarely seen. Now, ultracold helium has become a commodity for physics research. In Wolfgang Löffler's lab, it is ready at hand thanks to a coffee machine of sorts.
The coldest place on earth
It was back-breaking work in 1908. For years, physicist Heike Kamerlingh Onnes had been building the ‘coldest place on earth’ in the Natuurkundig Laboratorium, the present day Kamerlingh Onnes building on the Steenschuur street. Intricate webs arose of tubing, thermometers, manometers, pressurised vats and Dewar vats, pumps, switches and other machinery.
It was Big Science avant la lettre, long before particle accelerators, moon landings or gravitational wave detectors were conceived. On that tenth of July, 111 years back, at seven thirty in the evening, it all paid off: for the first time, helium became a liquid, at a temperature of -269 degrees centigrade.
Halvium
One tea cup of liquid helium was the full yield of all the hard work, with help from his wife Bé feeding him bread, and from technicians such as the legendarily able Gerrit Jan Flim. ‘Once the fluid surface had been noticed, we didn’t lose sight of it. It was razor clear against the vessel wall’, wrote Onnes imaginatively in his report.
Only a few months earlier, writes Dirk van Delft in his biography of Kamerlingh Onnes, he made a fool of himself when he mistook a white, flaky cloud in his apparatus for solid helium. The world press wrote about the scoop, a nice victory over Onnes’ competitor James Dewar in Londen. However, the flakes turned out to be hydrogen, and Onnes had to swallow his claim. Van Delft writes how Onnes’ students joked about ‘halvium’ (a pun on ‘helium’ in Dutch, since ‘heel’ means ‘whole’). ‘A joke that Onnes did not care much for.’
Coffee machine
But this time, success was certain. Three years later, Kamerlingh Onnes discovered superconductivity, a phenomenon that has been keeping physicists busy ever since. In 1913, Kamerlingh Onnes won the Nobel prize, and the Leiden helium monopoly lasted until 1923.
How much things have changed. Anyone in need of liquid helium can order a Montana Cryostation® for the price of a luxury car. The Cryostation has the size of a table coffee machine, and comes with a complimentary sample holder for measurements, which ensures that vibrations of the pumps don’t spoil the measurements.
‘We got it on Tuesday, it was working by Thursday’, says Henk Snijders, postdoc in physicist Wolfgang Löffler’s lab in the Huygens Laboratorium
Commodity
It’s a cryocooler, explains Snijders, in which gaseous helium circulaties. This will yield cooling down to a 271 to 272 degrees centigrade, 2 to 3 Kelvin. Snijders uses it to investigate quantum dots, tiny semiconductor structures on a nanometer scale. ‘Actually, helium doesn’t need to become liquid in here’, says Snijders, ‘even though droplets will probably form from time to time.’
In 111 years, liquid helium has evolved from being a Nobel bagging scoop to a simple commodity. Leiden still hase a Cryogenic department, which provides liquid helium by the liter: ‘One advantage of this system is that it is a closed system, so you don’t lose your helium. And you don’t have to go all the way downstairs to get it.’