Introduction

This user guide will help scientists and technicians correctly use the ASC Scientific IM10/ IM10-30 Impulse Magnetizers (Figure 1). The IM10/IM10-30 Impulse Magnetizer (hereafter referred to as IM10 unluess otherwise noted)  is used to impart isothermal remanent magnetism (IRM) by exposing the sample to a short burst of a large magnetic field. The field is produced by the discharge of energy from a capacitator bank through a coil surrounding the sample cavity. The capacitator bank is first charged to the desired voltage (corresponding to the desired field). It is then discharged through the coil very quickly to magnetize the sample.

IRM is the form of remanence produced in hysteresis experiments and is acquired by ferromagnetic grains with coercive force less than the applied field. The maximum remanence that can be produced is called the saturation isothermal remanent magnetization (SIRM). The field at which saturation is reached depends on the composition and microstructure of the specimen.

Coercivity of remanence is a very useful hysteresis parameter that can be used in determining magnetic mineralogy and grain size and in helping to characterize magnetic mixtures. It is the field that reduces the saturation isothermal remanence to zero.

The impulse magnetizers are ideally suited for the study of acquisition of IRM and the coercivity of remanence of discrete samples. Both are characteristic rock magnetic properties that are used for a preliminary magnetic carrier identification.

The ASC IM-10 impulse magnetizer is capable of imparting a magnetization of up to 1.2 T while the IM10-30 is capable of imparting a magnetization of up to 5T. The desired charging voltage can be approximately adjusted with the voltage adjustment knob and is precisely displayed on the charging voltmeter. The charging voltages corresponding to specific field levels for the unit on board are given in Appendix X.

Caution: The magnetizer produces a strong magnetic field capable of remagnetizing material within 1 m of solenoid.

Procedures

1. Turn the "Power" switch on. No warm-up period is necessary.
2. Place the sample in the holder in the desired position. Insert the holder into the sample cavity until it hits the back of the cavity.
3. Set the voltage adjustment knob so that the ascending voltage displayed on the meter approaches the desired charging voltage slowly. There is a lag time between adjusting the voltage knob and charging of the capacitors to a given voltage. The set voltage is approached asymptotically over a 30- to 60-s time period. The voltage buildup can be monitored via the digital meter. The most accurate and reproducible results will be obtained if the adjusting knob is set to a point slightly above the desired voltage, so that the desired voltage is approached at a rate of 0.5 V/s.
4. Allow the charging voltage to ascend to the desired value and push the trigger button. For most accurate and reproducible results, do not press the trigger button if the voltage is still building rapidly.
5. If you overshoot the desired voltage, push the trim button until the displayed voltage drops below the desired value. Allow the charging voltage to ascend to the desired value and trigger.
6. Measure the induced magnetization in the cryogenic magnetometer or with the spinner magnetometer.
7. At the end of each work session, turn the voltage adjustment knob fully counterclockwise and trigger the circuit before turning off the power.
8. Note: after being magnetized, samples with a high concentration of magnetic minerals may become too strong to be measured in the SRM. In this case a small rock chip can be used for IRM acquisition experiments or SIRM determinations.

Orienting the Samples

The ASC IM10 impulse magnetizer produces a positive field coming out of the coil towards the user.

The ASC IM10-30 impulse magnetizer produces a positive field going into the coil, away from the user.

Coil Installation and Removal (IM10-30 only)

The IM10-30 impulse magnetizer is equiped equipped with interchangeable coils. Each coil is unique and has its own charging voltage to desired field table. Charging voltage tables for each coil are presented in Appendix X. Follow the steps below to change the coils.

1. Hold the coil with the scribed line on the edge of the front face of the coil pointing up (12 o'clock).
2. Push the coil into the cavity on the front panel of the unit until the coil protrudes out of the cavity about 2 cm. Align the scribed line on the coil with the scribedon the front face of the cavity and push the coil in the remaining distance until it protrudes by only about 2 mm
3. Screw on the retaining ring until it tightens against the face of the coil. Lightly hand tighten only! You are now ready to use the instrument.
4. To remove a coil, unscrew the retaining ring. To remove the  #2 coil, insert index and middle fingers of each hand into the sample cavity with your thumbs against the front face of the cavity. Pull the coil straight out. To remove the #3 coil, turn the handle of the coil extractor counterclockwise a couple of turns while holding the rubber end. Insert the rubber plug of the extractor into the sample cavity and while pressing it against the side of the cavity, turn the handle clockwise until the plug expands enough to fit snug inside the coil. pull the coil out about 5 cm. Unscrew the handle a few turns until the extractor can easily be removed. Pull the coil straight out. To remove the #4 coil , insert the plastic handle of the extractor slowly into the sample cavity. With a quick jerk, pull the coil out of the cavity about 5 cm. A small finger may also be able to accomplish this. Next, slowly pull the extractor or finger out of the coil and pull the coil straight out.