Towards magnetic liquefaction of hydrogen: experiments with an active magnetic regenerator test apparatus

Refrigeration based on an Active Magnetic Regenerative (AMR) cycle has the potential to be a more efficient way of liquefying hydrogen than conventional gas cycles. Because the magnetocaloric effect decreases quickly for most materials as the temperature moves away from the phase transition region, the combination of many magnetic refrigerants in a multi-layers active magnetic regenerator is needed as a way to produce larger temperature spans for each stage of a liquefier. An investigation of a multi layer regenerator has been performed using an AMR test apparatus (AMRTA). Gadolinium and a gadolinium-terbium alloy were used as the two layers in the fabrication of two reciprocating multi-layer regenerators working near room temperature. The performances of the multi-material regenerator is compared to a Gd regenerator in terms of temperature span (respectively 20 K and 16 K at 2 Tesla respectively) and cooling power. For the first time, a multi-material AMR has been shown to produce a larger temperature span and cooling power than a single material of equivalent mass and geometry. (author)