Guida all’uso del magnetometro criogenico del laboratorio di paleomagnetismo dell’Istituto Nazionale di Geofisica e Vulcanologia

Abstract

The idea of writing a technical report on the cryogenic system installed at the INGV paleomagnetic laboratory has come when it was decided to upgrade the old control software; originally, the system was driven by the Visual C++ program 2GLC, working on a Pentium 75 Mhz PC on Windows NT 3.5 Operating System. The new software, developed in LabView, forced us to upgrade the PC to a new one able to run Windows 98/Me operating system; it was decided to use an old Pentium I or II generation mainboard with simply a faster clock, to have ISA bus still available and to continue using the multi-serial RocketPort board to interface the magnetometer controllers to the computer; it was not necessary, in this way, to change all the cables due to the plug differences in the new RocketPort models.
The most critical stage in replacing the control software (and the operating system) was in finding the new settings; some of these were not a problem, since they were identical to the ones used before, but it was necessary to change all the values related to the positions of the subsystems (home positions, left and right limits, susceptibility probe, AF coils, SQUIDs, IRM coil), due to the different reference position employed by this new program.
The first part of this note concerns all the settings needed to run correctly the system; it is obvious that the effective quality of the measurement strictly depends on the precision by which we individuate the SQUIDS sensor, and that, for example, a perfectly axial IRM or AF demagnetizing field is achievable only when the center of the coils is reached by the sample.
The best possible precision was also used to calculate the real “length” of the SQUID sensors, that means, practically, the least spatial resolution of the instrument when measuring u-channels; new measurement curves for the magnetization of a dipole (placed along the three axes) vs distance on the track were achieved to precisely detect the sensors’ position and to evaluate the real volume “felt” by the sensors measuring in continuous mode.
The next big change in the new software is...