Simple, Inexpensive Liquid Helium Temperature Controller, Using Integrated Semiconductor Circuits

Abstract

We describe a controller for regulating the temperature of a pumped liquid helium bath. The controller is a considerable improvement over previous controllers in that it is much simpler and less expensive. These improvements are due mainly to an uncommon direct‐coupled alternating current circuit, and to extensive use of the recently introduced integrated semiconductor circuits. The controller operates by measuring the resistance of a carbon radio resistor immersed in the liquid helium bath, and then feeding back a proportional correction current to a heater. The controller will control a bath to within 100 μK over a period of 20 min, at 2.1 K, and could be used to control the temperature of a copper block over a wide range of temperatures.