Hall Probe Measurement Bench
The Hall probe measurement bench enables point-by-point measurement of magnetic fields produced by insertion devices and magnets. The bench has a Hall probe mount movable in three axes, with a position resolution (as measured by optical encoders) of 1μm in all three directions. The range of movement is as follows:
A selection of different Hall probes are available depending on the magnet aperture, field direction and magnitude. Probes are attached using a flexible mounting arrangement which can be tailored to meet the needs of the specific magnet under test.
Movement of the probe and data acquisition is controlled from a PC. Aligning a magnet to the bench is usually carried out by moving the probe to several reference points on the magnet and adjusting the angle of the magnet to the bench based on encoder readings.
Flipping Coil Bench
The flipping coil bench is typically used to characterise the integrated field of long insertion devices. A long coil is stretched between the two ends of the device, and rotated through 180° about the ID axis. The integrated voltage induced in the coil is proportional to the integrated field along the length of the ID. This information can be acquired using Hall probe measurements, but is susceptible to accumulated small errors. A flipping coil measurement can give greater accuracy.
The two ends of the flipping coil are mounted on horizontal and vertical movement stages, with a resolution of 1μm. Data acquisition and movement is controlled from a PC.
The pulsed-wire technique involves passing a pulse of current along a single wire through an insertion device. The magnetic field of the device induces a small transverse movement in the wire, which can be picked up using a laser/photodiode pair mounted downstream of the device. We have equipment in the lab to carry out these measurements, but the technique has not been verified in this lab yet.
The lab has a pair of Helmholtz coils for permanent magnet characterisation. A PM block is placed in the centre of the coils and rotated through 180°. The voltage induced in the coils is proportional to the magnetisation strength of the PM block along the axis of rotation. Using this setup, the strength in all three directions can be characterised, allowing for accurate 'sorting' of PM blocks within an ID array.
A large dipole magnet and stable power supply are used to calibrate Hall probes. The PSU supplies up to 140A/76V with a stability of 10ppm, giving a maximum field in the dipole of 3.5T. The central field in the dipole is uniform over a wide area. An NMR teslameter is used to give an absolute field reading to an accuracy of 5μT. This system is used to provide an absolute calibration of the Hall probes used in the lab.
For further information please email AMICI@stfc.ac.uk