The OptistatDN cryostat cools samples using liquid nitrogen from an integral nitrogen reservoir. Liquid nitrogen, stored in the upper part of the cryostat, is gravity fed to a heat exchanger surrounding the sample tube. The sample is then cooled by conduction via a helium or nitrogen exchange gas in the sample space.
A vacuum case surrounds the nitrogen reservoir and heat exchanger. It needs to be pumped to high vacuum (lower than 10-4 mbar). An activated charcoal sorb is fitted to the nitrogen reservoir. This continuously pumps the residual gases from the OVC to maintain good thermal isolation.
Changing the sample simply involves removing the sample rod maintaining overpressure of exchange gas , replacing the sample and inserting the rod back into the cryostat. There is no needs to break the insulating vacuum and warm the cryostat up. The resulting sample change times are very short, typically few minutes.
Temperature control is achieved by a combination of manual nitrogen flow control and power dissipated in an electrical heater, regulated using a temperature controller.