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.

Our high temperature interfaces use a unique combination of mechanical and thermodynamic properties to create a high temperature thermal disconnect between the cold head and the sample space. This allows for heating of the sample space far in excess of the maximum 355K temperature of our cryocoolers.

450K The easy way

Our 450K interface is a simple semi-perminant addition to the cold tip that expands the upper sample temperature range by 95K utilizing most of the same instrumentation as our standard cryocoolers.

800 K Pouring on the Heat

Our specially design 800K interface goes beyond the standard techniques to provide a unique system that maximizes thermal conduction at low temperatures while minimizing heat transfer at high temperatures. Beyond the safe operating temperature of Silicon Diodes the standard sensors are replaced with E-type Thermocouples and Platinum RTDs.

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.

Whether the measurement is optical or electrical in nature, the sample large or small, we have a sample holder for almost any measurement. The LT3B can accept all but our largest sample holders. As will all of our cold fingers the LT3 has a 1/4-28 threaded hole on the cold tip to mount the sample holder. So even if you do not find what you need from our wide variety of sample holders there is always the option of attaching a custom sample holder.