Magnetic Measurement Lab - Home - Walter Scott, Jr ...Magnetic Measurement Lab Equipment •...

Magnetic Measurement Lab Equipment

• Gaussmeter o Lake Shore 425 o Transverse Hall Probe

• Power Supply o B&K Electronics o 3 Channels

• Quadrupole Magnet • Multimeter • Translation Stage

Precautions Induced voltages: Do not disconnect the magnet from the supply when the supply is powered! Be very careful with the hall probe. It is expensive and we only have one. To Do

• Read manuals for the Gaussmeter and power supply. Note the details of probe geometry (see earlier viewgraph).

• Measure magnet resistance • Attempt to count turns in the coils • Measure magnet radius • Calculate current and voltage required to generate a pole tip field of 1 kG • Measure magnet core length and width • Determine center of quadrupole • Devise a method to determine micrometer set points that would place the Hall probe tip

at the center of the magnet

• Place Hall probe o Longitudinally centered o Vertically centered o Horizontally offset by 1 cm

• Ramp up magnet current to the calculated “1 kG setpoint” o Is the poletip field what you think it should be? o Where does the difference come from?

• Ramp the current up to 10% higher than the “1 kG setpoint” then slowly back down to 0 o Repeat 5 times

§ This should take about 5 minutes with roughly 10% steps at a time o Finish by ramping up to the 110% current and then back down to the 100%

current point § The magnet is now standardized § You should be noting all measurements along the way

• Plot the data B/I for each cycle to ensure that the last and the next to last cycles are basically identical.

o B/I is used to get rid of the primary slope of the B vs H(I) plot so that one can see the hysteresis more clearly.

• Leave the current at that setpoint • Move the hall probes transversely to measure the vertical field as a function of horizontal

position o Plot out the data and fit

§ Perform error analysis based on the specs of the Gaussmeter and power supply

§ Was zero where you thought it should be? § The goal here is to make an accurate determination of the guadrupole

gradient • Move the probe to 1 cm,0,0 (x,y,z) • Back the probe out completely until the field goes to zero

o Did you remember to zero the field at the beginning? o Now measure the longitudinal profile of the field over 1,0,z

§ Plot out and integrate the plot § Divide the integral by the peak found at 1,0,0

• This is the effective field length • What is your certainty in this measurement?

• Mount a second quadrupole on the box beam so that the iron to iron distance is 4 cm o Repeat the longitudinal profile measurement

§ What differences did you find?