“Clean” Liquid Helium

Liquid helium is the coldest fluid that exists in nature. By virtue of this fact, any unwanted substance present in liquid helium, that is, any impurity, will be “frozen” and will be in solid form. In practice, these solid impurities can be easily eliminated to obtain “optically clean” liquid. However, even “optically clean” filtered liquid helium may contain a non-negligible quantity of molecular hydrogen. These minute traces of molecular hydrogen are the causes of a known problem worldwide: the blockage of capillary tubes in helium evaporation cryostats. This problem seriously affects a wide range of cryogenic equipment used in low-temperature physics research at a considerable operational cost increase. In this chapter, we propose an underlying mechanism for this effect and provide a definitive solution by means of production of hydrogen-free liquid helium, that is, not only “optically clean” liquid helium but completely “clean” liquid helium. Moreover, basic superfluidity research studies could benefit from the availability of “clean” liquid helium

Crystal structure and magnetism of Co(HPO3)⋅H2O: A novel layered compound of Co(II)

Under the terms of the Creative Commons Attribution (CC BY) license to their work.-- et al.The crystal structure and magnetic properties of Co(HPO3)⋅H2O have been determined. The solid crystallizes in space group P c a21, a=8.984(2) Å, b=7.918(2) Å, c=10.139(8) Å, V=721.2 Å3. Z=4 d calc =2.89 g/cm3. The structure consists of layers only connected by hydrogen bonds. These layers can be viewed as formed by zigzag chains of edge‐sharing Co(II)O6 octahedra interconnected by a three atom bridge (O‐P‐O) and a single oxygen bridge. ac magnetic susceptibility measurements show a sharp peak at T c =(10.8±0.1) K, and are consistent with a transition from one‐ to two‐dimensional magnetic order, in agreement with the structure. An analysis of the χT/C vs ε=(1−T c /T) data in the critical region, for T>T c , using a double‐logarithmic plot, yields a critical exponent γ=1.75 for 0.01<ε<0.1, which correspond to a two‐dimensional Ising model.The financial support of the Spanish Commission Interministerial de Cienda yTecnologia (C.I.C.Y.T. No. BP086-0187) is acknowledged. M. D. M., P. A. and F. S. thank the Spanish Ministerio de Educacion y Ciencia for predoctoral fellowships and P. G. R. for a postdoctoral fellowship.Peer Reviewe

Purification of recovered helium with low level of impurities: evaluation of two different methods

Helium gas coming from low temperature experimental systems is recovered to avoid losses of this scarce gas on Earth. Once this helium gas has been recovered and before its liquefaction, the impurities contained should be removed. It is possible to achieve a low level of impurities by using the proper materials and procedures on the road to helium recovery. A comparison of two different methods applied for the purification of recovered helium with low level of impurities is reported in this paper. One method is the use of liquid nitrogen traps and the other one is the application of a purification system based on getter materials. The cleaning efficiency has been probed experimentally for both methods through the analysis of the purified He gas. The evaluation covers the life time between regenerations, the everyday care as well as the long term, the energy consumption, the initial investment besides the cost of maintenance of both methods

Enhancement of the Liquefaction Rate in Small-Scale Helium Liquefiers Working Near and Above the Critical Point

Low-temperature research laboratories with typical liquid-helium consumption of the order of tens of liters per day have greatly benefited from the recent development of small-scale liquefiers. In general, these liquefiers are based on Gifford-McMahon or pulse-tube closed-cycle refrigerators with a nominal cooling power ranging from 1 to 1.5Wat 4.2 K. The liquefaction rate for these cryocooler-based liquefiers depends on the pressure at which the helium is liquefied, although the final user conditions of the produced liquid helium are always atmospheric pressure and boiling temperature (e.g., 4.2 K at 100 kPa). Here, we show a systematic study on this effect, in which an enhancement in excess of 70% in liquefaction rate is found experimentally for pressures near and above the critical point of helium (220 kPa). We propose that the underlying mechanism for the liquefaction enhancement is based on the increase in cryocooler cooling power with temperature and the decrease of the helium enthalpy with pressure

New ATL developments

Trabajo presentado al ATL user workshop, celebrado en Zaragoza del 23 al 24 de octubre de 2018.Peer Reviewe

Recuperación de He con empresa Internacional Americana y Japonesa

Trabajo presentado al 8º Foro Europeo para la Ciencia, Tecnología e Innovación (TRANSFIERE), celebrado en Zaragoza (España) del 13 al 14 de febrero de 2019

¿Es el helio líquido una sustancia pura?

Trabajo presentado al II Congreso del Instituto de Ciencia de Materiales de Aragón: “Materiales para los retos de la sociedad", celebrado en Jaca (Huesca) del 2 al 3 de febrero de 2017.Peer Reviewe