laboratory notes J. Appl. Cryst. (2020). 53, 297–301 https://doi.org/10.1107/S1600576719016704 297 Received 25 September 2019 Accepted 13 December 2019 Edited by D. Pandey, Indian Institute of Technology (Banaras Hindu University), Varanasi, India Keywords: cryostats; cryogenics; neutron scattering; sample environment. A fast-cooling sample-positioning probe for low- temperature neutron scattering experiments Andrew Manning,* Maxim Avdeev and Paolo Imperia Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Australia. *Correspondence e-mail: andrew.manning@ansto.gov.au Top-loading exchange gas cryostats have for a long time been a widely used sample environment device for a variety of neutron scattering experiments. In particular, they allow for simpler and faster changes of samples mounted on sample-positioning probes than is possible with bottom-loading cryostats under vacuum. Here, a new design for sample probes using composite materials is investigated, which significantly decreases the time required to cool a newly installed sample in two different types of closed-cycle exchange gas cryostat. 1. Introduction Cryostats are fundamentally important sample environments for neutron scattering experiments. In particular, ‘top-loading’ cryostats, which use an exchange gas to thermalize the sample, are widely used as they allow faster and simpler sample changes compared with ‘bottom-loading’ cryostats which require that the refrigerator be warmed to ambient tempera- ture and vented to atmosphere. Modern top-loading cryostats broadly fall into three categories characterized by their cooling mechanism, each of which are regularly used at the Australian Centre for Neutron Scattering (ACNS; https:// www.ansto.gov.au/research/facilities/australian-centre-for- neutron-scattering). ‘Wet’ cryostats with a liquid helium bath, such as the ‘orange cryostat’ (Brochier, 1977) as shown in Fig. 1, offer a high cooling power via the Joule–Thompson throttling process down to a base temperature of 1.5 K. However, this comes at the cost of the consumption of liquid nitrogen and helium and thus the requirement to refill the cryogenic liquids periodically during use. Alternatively, closed-cycle cryostats, which are directly coupled to a cryo- cooler such as a Gifford–McMahon (for example the Sumi- tomo RDK-408D2) or pulse-tube (e.g. Sumitomo RP-082B2) cold-head, provide a moderate cooling power down to around 1 W at 4.2 K and the ability to run without maintenance for extended periods. Finally, by combining aspects of these two designs, closed-cycle cryostats can also incorporate a pumped gas flow loop (Chapman et al., 2011) to achieve cryogen-free operation and the ability to reach a base temperature of 1.5 K for extended periods, but with the caveats of a much lower cooling power and thus longer system cool-down time, and a more complicated setup. Although the mechanism for achieving cooling is different in these three cases, temperature control occurs in the same way from the perspective of the sample to be investigated. First, the sample is mounted on the end of a sample- positioning probe which is fitted with a thermometer and ISSN 1600-5767 # 2020 International Union of Crystallography