HOT GAS TEMPERATURE CONTROLLER FOR A CRYOSTAT INSERT HAVING HIGH-STABILITY

A very low-noise, variable temperature insert for a standard liquid-he lium cryostat has been developed. The design provides a 10-100 K opera ting range, with temperature stability better than 20 mK in the range 25-100 K, improving to 2 mK below 25 K. This temperature stability fig ure is obtained by balancing the cooling power due to the thermal coup ling of the sample to liquid helium, with the heating power of a strea m of room-temperature He gas flowing through a heat exchanger. The hea ting power is continuously regulated within a feedback loop by throttl ing the gas flow with a proportional valve, using the error signal fro m the temperature controller. The system provides good temperature sta bility without the need for low-resistance leads in the vicinity of th e sample holder as those needed to feed an electrical heater. This is relevant to experiments where electromagnetic interference must be min imized. (C) 1997 American Institute of Physics.