Neon gas-gap heat switch I. Catarino a, * , G. Bonfait a , L. Duband b a Cefitec – Faculdade de Cie ˆncias e Tecnologia da Universidade Nova de Lisboa, Campus de Caparica, 2829-516 Caparica, Portugal b Service des Basses Tempe ´ratures, DRFMC, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France Received 6 July 2007; received in revised form 28 August 2007; accepted 4 September 2007 Abstract A self-contained neon gas-gap heat switch featuring an internal charcoal adsorption pump has been developed and tested. This heat switch can be used with cold base temperature ranging from 17 K to 40 K offering an extension to sorption based helium gas-gap heat switch limited to below 20 K. For this prototype, an ON conductance about 74 mW/K and an OFF resistance about 3000 K/W were obtained, giving an ON/OFF conductance ratio about 220 at 20 K in agreement with calculations obtained from a simple model. These characteristics can be further optimized working on the geometry. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: A. Adsorbent; B. Neon; C. Thermal conductivity; C. Heat transfer; F. Space cryogenics 1. Introduction Cryogenic heat switches are one of the key technologies in many cryogenic systems. Indeed the ability to make or break a thermal contact finds direct applications in numer- ous devices. It can be used to produce adiabatic environ- ments, to couple/decouple a redundant cryocooler from the operating one, to decrease the cooling time in a tran- sient operation, to control the temperature gradient and thereby allow to manage the liquid phase in specific closed cycles [1], to control Energy Storage Units [2], etc. Many cryogenic heat switches based upon different physical mechanisms have been developed in the past [2]. However, if high reliability is needed as well as a minimum of moving parts, as for instance in thermal space buses, the so-called gas-gap heat switch (GGHS) using a sorption pump is one of the best solutions. For instance, for GGHS working with helium, ON conductances ranging from 35 · 10 3 W/K [3] to 3 W/K [4] and OFF conductances ranging from 1500 K/W [4] to 77 · 10 3 K/W [3] at 4 K, depending on the geometry and purpose, were reported. Unfortunately, up to now, this kind of switch was mainly used with helium gas and then limited to temperature below 20 K. In this article, we describe a GGHS working between 17 K up to about 40 K, using neon as the conducting gas and a mini- ature cryogenic adsorption pump (activated charcoal) to manage the gas pressure. After a brief description of the physical mechanism used in a GGHS and particularly on the working temperature range, we describe our prototype and the simple thermal model used to calculate its characteristics. Its performances, such as the ON and OFF thermal resistance values as well as the sorption temperature needed to actuate this switch, were measured and compared to our calculations. The very good agreement found shows that the characteristics of such heat switch type can be confidently extrap- olated for other gases and consequently for other temperature ranges. 2. Low temperature gas-gap heat switches In its most common form, the hot and cold terminals of the gas-gap heat switch are two coaxial copper blocks sep- arated by a thin cylindrical gap which is filled with or emp- tied of gas to achieve the switching action (Fig. 1). A 0011-2275/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.cryogenics.2007.09.002 * Corresponding author. Tel.: +351 212948576; fax: +351 212948549. E-mail address: isacat@fct.unl.pt (I. Catarino). www.elsevier.com/locate/cryogenics Available online at www.sciencedirect.com Cryogenics 48 (2008) 17–25