The Helitran® incorporates an extended surface tip heat exchanger (Matrix Heat Exchanger)  which provides efficient heat transfer between the helium and the sample mount.  The Liquid helium flows through this heat exchanger and as the latent heat of  vaporization cools the sample mount,  the liquid evaporates, the gas continues to flow through the exchanger providing additional cooling (capturing the enthalpy of the gas) to the sample mount.  If the flow is optimized the helium gas will exit the Matrix Heat Exchanger at a temperature equal to the sample temperature.

The consumption of He during initial cooldown is 40 times higher without an extended surface cryostat tip heat exchanger from 300K (room temperature) to 4.2K and 14 times higher when cooling from 77K to 4.2K.

Conventional helium flow cryostats utilize a capillary tube in a vacuum jacket with super insulation to reduce the radiant heat load.  However as the helium absorbs radiant heat the liquid is vaporized and forms bubbles of gas which have a larger volume than the liquid thus forming a temporary block to the flow of the liquid called “vapor binding”.  At the delivery end of the transfer line this results in the liquid/gas mixture being delivered in spurts with accompanying pressure and temperature cycling.

The coaxial flow transfer line incorporates a shield flow surrounding the tip flow for the entire length of the transfer line.  The entrance to the coaxial shield flow tube is provided with a nozzle which results in a pressure and corresponding temperature drop in the shield flow which cools the tip flow in the center tube. This cooling prevents boiling and gas bubble formation in the helium, even at very low flow rates.  The Helium is delivered at the sample end with the desired temperature stability and low vibrations.

From our standard offerings of single strand copper and low noise coaxial wiring packages, to any number of custom wiring configurations, our technicians painstakingly wrap each cold head for optimum thermal anchoring.

Typical instrumentation for temperature measurement and control include, one 36 ohm thermofoil heater, one curve matched silicon diode for rough temperature control, and one free length calibrated diode for direct attachment to the sample or sample holder for accurate temperature measurement. Silicon diode sensors are favored heavily for most standard applications, because of their low cost, durability, and stability, but we do offer a wide variety of other sensors for different applications such as Cernox sensors for high magnetic fields, E-type thermocouples for 4 K - 800 K measurements, and Platinum RTD's for accurate high temperature measurements.

Our wide selection of wiring and instrumentation is matched by an equally wide selection of temperature controllers from Cryocon, Lakeshore, and Scientific Instruments.