Dipole Field Monitoring Electron Arm

(see special instructions for running the Hadron Dipole in field regulation mode)

Basic Setup

Each spectrometer dipole magnet is equipped with a Metrolab PT 4025 NMR Teslameter, several field probes, and multiplexers (to allow switching between the probes). Details of the operation and theory of operation for the Teslameter can be found in its user manual, a copy of which is available in the the counting house. The basic layout is shown in Figure 4.7

Figure 4.7: Basic layout of NMR system

1.

The "Gap Probes" (Group 0 in the controls) are located in two groups of three; one group on the low field side of the gap and the other on the high field side of the gap. The groups of three are made up of one each of the manufacturer's type 3, 4 & 5 probes, designed to cover different field ranges (see Table 1). The six ``Purcell Gap Probes'' (Group 1 in the controls) are located in the Purcell gap of the magnet and consists of two each of the above types. Note: Since the fall of 1998 the multiplexer-multiplexer in the electron arm, MUX 2032, has been bypassed and hence the ``Purcell Gap Probes'' are currently unavailable. There are no plans to fix this multiplexer in the immediate future.

The "Gap Probes" are equipped with coils which provide a field gradient that cancels out the field gradient of the magnet in the vicinity of the probe. These gradient compensating coils are part of a simple circuit that is completely independent of the Teslameter. The basic circuit for the compensating coils is shown in Figure 4.8

Figure 4.8: Gradient Compensating Circuit.

1.

Figure 4.9: Control Voltage calibration for Electron Dipole.

1.

Figure 4.10: Control Voltage calibration for Hadron Dipole.

1.

Figure 4.11: DAC Calibration for manual operation of NMR probes.

1.

The following graphs (see Figures 4.9, and  4.10can be used to determine optimum values for the compensating coil control voltage. It should be noted that the setting of the compensating coil current is not very critical in most cases. In general if you're within 10% of the correct value everything should work fine.

Table 4.4: Dipole NMR probe field ranges

Probe Type	Field Range (T)
3	0.17 - 0.52
4	0.35 - 1.05
5	0.70 - 2.10