Field stability study

Results of magnetic field stability study (August 2014): Media: field_stab.pdf‎

• The field is stable with time well within our 10^-3 accuracy goal. There is a 5 Gauss shift after the power supply trip at the end of day one, although the same power supply setting was restored. The influence of the solenoid field (1200A) is at the one Gauss level when the pair spectrometer field is at its nominal 1.8T. We noticed a ~20 Gauss field in the pair spectrometer when the Solenoid was at 1200A and the pair spectrometer power supplied turned off.

• The Danfysik power supply readout is precise. There will be no need for a DCCT. Some of the small field changes seem to loosely correlate with small change in the power supply output.

• The Hall probe is stable and correlate well with the NMR probe in spite of their different locations. (The NMR probe is at the center of the magnet. The Hall probe is on the side, outside the vacuum chamber. We added a 135 offset to the Hall probe field to have it on the same plot)

Field dependence with temperature (August 2014): Media: field_stab.pdf‎ There is clear field dependence with temperature. However, it is very small (). We do not expect such large changes of temperature: To increase the temperature by 4 degrees, we closed the flow valve by 90%. In conclusion, the temperature effect on the field is well below our accuracy goal and can be neglected.

• In conclusion, a Hall probe and the Danfysik power supply readout will be enough to monitor the stability of the field during operations.