Cryogen
Free ESR Systems
Cryogenic
offers a + 16 Tesla 5ppm magnet with a large
room temperature bore. The magnet is permanently fitted with leads
and a superconductivity switch for persistent mode
operation.
ESR measurement systems require high
homogeneity, which can be maintained over a wide range
of fields. Experiments are performed at fixed frequency
and the spectrum is obtained by sweeping the magnetic
field. This requires the field to be stable in spatial
homogeneity and change steadily and repeatedly over
time. As the spectra can vary considerably in width it
is essential to be able to control the magnet current
and therefore the field accurately over a wide range of
field with sufficient precision to see narrow
resonance's.
With a cryogen free system it is not
necessary to reduce helium consumption, as there is no
liquid helium to evaporate. Instead it is merely
required to have accurate and smooth ramping of the
magnet current. With the Cryogenic power supply it is
possible to set and measure the current accurately and
perform sweeps by maintaining and regulating a small
levitate across the inductance of the magnet.
The magnet is made from NbTi and NbSn
superconductors with truly superconducting joints to
provide good persistent mode performance. A single
magnet power supply is provided for the magnet. The ramp
rates available are from approximately 10-8 to 10-3 per
second of full value. A single current transducer is
supplied to measure the current to 1pppm and output the
result to the computer on the IEEE bus. A control
computer is used to control the magnet field and to
drive the temperature controller using the GPIB
interface.
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