System Description
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4.3 Link between the Host Computer and the AQS
Although during a typical TopSpin session this link is permanently in operation and effectively
invisible to the user, the link is broken anytime either the host computer or the console is
switched off and must be re-established when they are switched back on. This will be done
automatically.
4.4 Magnet, Shim System, HPPR and Probe
The magnet generates the magnetic field required to induce NMR transitions. To maintain a
superconducting system the magnet core is cooled to very low temperatures using liquid
nitrogen and helium (for more details see the section The Magnet and Magnet Dewar
[}27]).
The room temperature shim system, mounted into the lower end of the magnet, is a set of
current carrying coils (known as shims) used to maximize field homogeneity by offsetting any
existing inhomogeneities. The currents in these room temperature shims (so called as they
are not cooled by being immersed in a bath of liquid helium) are controlled by the BSMS and
may be adjusted from the BSMS display to optimize the NMR signal. This has a major effect
on signal resolution and sensitivity. This action of adjusting the currents in the room
temperature shims is referred to as shimming the magnet.
Figure4.3: Photo of Magnet, Shim System, Probe and HPPR
1 Operator Console 5 Probe
2 Console 6 Shim System
3 Magnet 7 Probe and Shim System
4 HPPR/2 Cover 2 Module with
Connections to the Probe
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