Gamma-ray laser moves a step closer to reality

A physicist at the University of California, Riverside, has performed calculations showing hollow spherical bubbles filled with a gas of positronium atoms are stable in liquid helium.

Method for cooling a superconducting accelerator cavity

Fermilab scientists and engineers have achieved a landmark result in an ongoing effort to design and build compact, portable particle accelerators. Our group successfully demonstrated a new, efficient way to cool superconducting ...

New method for detecting quantum states of electrons

Quantum computing harnesses enigmatic properties of small particles to process complex information. But quantum systems are fragile and error-prone, and useful quantum computers have yet to come to fruition.

LS2 report: Before the return of the cold

Since the start of January, the liquid helium flowing through the veins of the LHC's cooling system has gradually been removed the accelerator and, one by one, the eight sectors of the LHC have been brought back to room temperature. ...

Energy-efficient superconducting cable for future technologies

For connecting wind parks, for DC supply on ships, or for lightweight and compact high-current cabling in future electric airplanes: scientists of Karlsruhe Institute of Technology (KIT) have developed a versatile superconducting ...

Scientists on making the Large Hadron Collider safer

An international research team headed by Evgeniy Talantsev, a senior research fellow at the Research and Educational Center of Ural Federal University, has approached the task of increasing the reliability of such complex ...

From turkeys to turn-keys

Last week, millions of Americans unwrapped a shrink-wrapped turkey for Thanksgiving. If so, they owe thanks to electron beams, which made the shrink-wrapping possible. But the electron beam can do a lot more: It can sterilize ...

Cryocooler cools an accelerator cavity

Particle accelerators are made of structures called cavities, which impart energy to the particle beam, kicking it forward. One type of cavity is the superconducting radio-frequency, or SRF, cavity. Usually made of niobium, ...

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Liquid helium

Helium exists in liquid form only at extremely low temperatures. The boiling point and critical point depend on the isotope of the helium; see the table below for values. The density of liquid helium at its boiling point and 1 atm is approximately 0.125 g/mL

Helium-4 was first liquefied on 10 July 1908 by Dutch physicist Heike Kamerlingh Onnes. Liquid helium-4 is used as a cryogenic refrigerant; it is produced commercially for use in superconducting magnets such as those used in MRI or NMR. It is liquefied using the Hampson-Linde cycle.[citation needed]

The temperatures required to liquefy helium are low because of the weakness of the attraction between helium atoms. The interatomic forces are weak in the first place because helium is a noble gas, but the interatomic attraction is reduced even further by quantum effects, which are important in helium because of its low atomic mass. The zero point energy of the liquid is less if the atoms are less confined by their neighbors; thus the liquid can lower its ground state energy by increasing the interatomic distance. But at this greater distance, the effect of interatomic forces is even weaker.[citation needed]

Because of the weak interatomic forces, helium remains liquid down to absolute zero; helium solidifies only under great pressure. At sufficiently low temperature, both helium-3 and helium-4 undergo a transition to a superfluid phase (see table below).[citation needed]

Liquid helium-3 and helium-4 are not completely miscible below 0.9 K at the saturated vapor pressure. Below this temperature a mixture of the two isotopes undergoes phase separation into a lighter normal fluid that is mostly helium-3, and a denser superfluid that is mostly helium-4. (This occurs because the system can lower its enthalpy by separating.) At low temperatures, the helium-4 rich phase may contain up to 6% of helium-3 in solution, which makes possible the existence of the dilution refrigerator, capable of reaching temperatures of a few mK above absolute zero.[citation needed]

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