This paper describes the basic structure of a two-stage pulse tube ref
rigerator. A novel phase shifter termed a double-orifice is introduced
. The machine was driven by a valved compressor and the on-off timing
was controlled by a computer and solenoids. The lowest temperature of
3.1 K at the cold end of the second stage was achieved. (C) 1997 Elsev
ier Science Ltd.