Dry Orange Cryostat

X. Tonon, E. Bourgeat-Lami, O. Losserand, S. Turc, E. Lelièvre-Berna
Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France

In the sixties, the cryostats consisted in a vessel filled with liquid nitrogen or helium suspended in a vac- uum tank. The cryostat was warmed up and opened for exchanging the sample and the consumption of cryogen was quite huge, especially at elevated temperature when a heater was fitted on the sample holder. The concept of the variable temperature insert developed at ILL in the seventies simplified enormously the life of the users. The Orange cryostat was born, featuring a top-loading access, a low boil-off allowing to hold a week-end, and a modularity facilitating the exchange of the tail.

In the eighties, several new generations of the Orange cryostat appeared. The first one, called Orange Cry- ofurnace, extended the high temperature limit from 320 to 550 K. This could be achieved by replacing the indium seal with a stainless steel/copper friction welded junction. The next ones extended the low limit with the addition of a dilution refrigerator (insert inside a cryostat and dilution cryostats).

During the last decade, the specifications of the cold heads have made big progress while the cost of the helium gas has increased. The total cost of an Orange cryostat (investment + operation) is still attractive but much less compared with a dry cryostat simplifying the work of users. We present a dry version of the Orange cryostat and the difficulties encountered with the use of cold-heads. Indeed their apparent ease of use hides a number of issues. In particular, the cooling power of a cold-head cannot compete with the presence of liquid helium and the impossibility to tune the cooling power generates temperature gradients. We compare the performances and conclude on the pros and cons of these wet and dry versions.