Minimizing pressure inhomogeneities across large samples under helium pressure media at low temperatures

Article type: Research Article

Authors: Leão, Juscelino Batista^{; *}

Affiliations: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA

Correspondence: [*] Corresponding author. E-mail: juscelino.leao@nist.gov.

Abstract: When using gas pressure media to achieve hydrostatic pressure under a constant pressure and volume, passing through the melting curve (P×T) of the gas to achieve low temperatures (1.5 K ⩽ T < 30 K) will cause an overall pressure reduction at base temperatures of at most 25 percent of the pressure read while under hydrostatic conditions at the P×T. In-situ inert gas high pressure vessels for neutron scattering for pressures of up to 1.0 GPa and temperatures as low as 1.5 K pose a particular problem due to the P×T phase diagram of the pressure media. A methodology for pressurization to ensure minimal pressure loss as temperature falls below the pressure media phase change, at the same time minimizing pressure inhomogeneity throughout the length of the sample; as well as calibration data are presented within this work.

Keywords: Pressure, hydrostatic, neutron scattering, helium, pressure gradient

DOI: 10.3233/JNR-210034

Journal: Journal of Neutron Research, vol. 24, no. 1, pp. 15-22, 2022