The hardware used for magnetization measurements is shown at the Fig.2. As Helmholtz Coils power supply the Kepco Power Supply Model BOP 20-10M is used. This model is high powered operational amplifier with full 4-quadrant, bipolar operation. It operates in remote control mode and is directed with using Digital Analog Convertor Model VMIVME 4145. The DAC works as Wave Form Generator of high linearity and accuracy. For Helmholtz Coils operation the sin wave form of output current with frequency up to 4 Hz and 9.5 A range is used. In measurement procedure the sine wave form sweeping up to 10 full periods has used. This form is seems more preferable as soon as it allows to get the maximal pick-up signals and the best signal-to-noise relation in the acceptable mode of the power supply operation. The signals from Power Supply current monitor output and two pick-up coils from each of foils are measured by multichannel Analog to Digital Converter Model HPE1313A. The sampling frequence 10 kHz is using. After measurements all ADC Data are saved for data processing. All electronic blocks are placed in VME-Crate at Hall A space. CODA Software Package, developed at CEBAF, is used for Data Acquisition and Processing. As usually the changing internal magnetic induction field produces in pick-up coil the induced voltage E. The pick-up voltage for positive and negative loops of magnetization process then is averaged on 10 periods and integrated over time to give the total change of the magnetic flux for each of foils. Typically, pick-up signal values from foil remagnetization are up to 50 mV in a peak. The air-flux level did not exceed 2 mV value, the noise level is less than 0.1 mV. For determination air-flux contribution the next procedure is used. The pick-up signal is measured for field sweeping near 9.0 A value in the 0.1 A range. In these conditions the foil is in saturation, the foil-flux contribution is a constant and induced voltage is only air-flux result. Then the air-flux contribution for full range sweeping can be precisely recalculated. This procedure was tested in a magnetization calibration measurements with using pick-up coil of a special design. This pick-up coil surrounding the foil had the extended dimension along a foil and could be placed with the zero profile to the field direction. In definite coil position the air-flux signal was decreased in hundreds times, and could be negligible. These two pick-up coils with different designs were used simultaneously and the saturation value results are in a good agreement. With using this procedure the air-flux subtraction should be repeated every times after angular position change, because the correlation between air-flux and foil-flux is depended from foil inclination angle. For air-flux subtraction after only one magnetization measurement we are using the next pick-up coils design and procedure. At the same foil position in 8 mm from foil edge two pick-up coils are used: one inside another with the same turn numbers. For these coils the correlations between air - and foil-flux are different. As result the single normalization calculations of two coils signal are needed for foil-flux separation. Only single above mentioned measurement of air-flux contributions for pair coils are needed. The resulting correlation coefficient has only geometry origin and is not changed with angle or field value (excepting near 90 deg foil inclination angle). In general any empty coil air-flux subtraction is correct only for foil full saturation state. Otherwise any subtraction procedures will be over-estimate or underestimate air-flux contributions.
Figure 2.
Figure 3.
Last Update: 1 August 1997
