Cryogen Free Magnet System 9-18 Tesla (CFMS)

The CFMS consists of the cryogen-free, high field superconducting magnet with integrated variable temperature sample space, cryocooler(s) and compressor(s), multi-channel temperature monitor, sample temperature controller and power supply. The cooling for the magnet and sample is provided by the cryocooler with a base temperature of less than 4K. The current to the magnet is supplied by a Cryogenic Ltd power supply using current leads of HTS conductor. A Lakeshore temperature controller controls the temperature of the sample.

The cryomagnet is delivered as a turnkey working system tested and ready to operate on delivery. No additional special equipment will be needed, nor will previous cryogenic experience be necessary to operate the system.

The magnet is produced using Cryogenic Ltd's proven technology for high field superconducting magnets. These magnets are manufactured using copper stabilised filamentary superconductor which is then vacuum-impregnated to form a composite structure of excellent mechanical strength and electrical insulation. The filament size and conductor type is chosen to eliminate flux jumps.

The magnet operates in vacuum and is cooled by conduction. It is passively protected against damage caused by accidental quench whether this is caused by mains power failure or by exceeding the operating temperature of the magnet or by exceeding critical current of the superconductor.

Integrated Variable Temperature Insert

The CFMS incorporates a variable temperature sample space cooled by gas flow. The same cryocooler is used to cool both the VTI and the magnet. Helium gas is circulated using a room temperature dry pump and cooled by the first and second stages of the cryocooler to 4K at which point it condenses into liquid helium. The liquid is collected in a small buffer tank just below the second stage. From here it is drawn off and expanded through a needle valve to achieve a temperature of 1.6K. The gas then passes through a heat exchanger controlled to achieve the set temperature and from there to VTI sample space. The standard temperature range is 1.6K-325K.

The temperature of the sample chamber is varied by using a heater and Cernox thermometer on the heat exchanger which is controlled by a temperature controller (Lakeshore 340).

Samples are top loaded into the sample access column via an airlock and gate valve located at the top of the VTI to allow access to the centre of the temperature-controlled region. Experienced operators can typically change samples in a few minutes.

A helium gas reservoir (50 litre NTP capacity) is supplied filled with helium gas at one atmosphere. The gas used is 99.995% purity and in the event of accidental contamination, when changing samples for instance, the gas can be replaced at low cost.