The engineers at Montana Instruments just completed this amazing feat:
There are over 100 DC wires plus four RF coax cables in the 4K sample space. The DC wires are connected through an extended double 50 pin D-shell ribbon connector side panel. Can you guess what the base temperature of this system is? The platform is at 3.3K and the sample is at 4.1K!
All wires leading into the sample space are made of phosphor bronze. Using the proper wire material is an important component of achieving the lowest base temperatures; see the chart below for wiring types and temperature rise contributions:
For a 6" wire length the temperature rise in milliKelvin is given below
Another important factor to achieving low base temperature is making sure that there is enough length of wire between each stage. Too short of a wire will cause Ohmic heating between the 30K stage and 4K stage or room temperature to 30K stage; too long of a wire will be difficult to manage and touches to a warmer stage can also cause an increase in base temperature. Generally if 6" of wire is used, 3" will run from the room temperature to 30K stage and the other 3" will run from the 30K stage to the 4K stage. Splitting the length of the wire between the stages is a good rule of thumb.If copper is hardwired to a component in the 4K stage, a wiring harness made of phosphor bronze should be used to bridge the connection from the 4K stage to the 30K stage. The copper wire can be coiled for wire management and then adapted to a phosphor bronze line.
With proper technique and a little patience the base temperature can be optimized. Montana Instruments understands low temperature challenges and can show you how to reach the performance needed for your research. Please contact our engineers about achieving the lowest base temperature for your system or to discuss your application.