10.6 Studies on HTS linear synchronous motor Ë 379Fig. 10.4:Profile of the magnetic field generated by the racetrack-shaped single-pancake
superconducting coil magnet whenIDC=40 A measured atz=10 mm [24].
Another superconducting coil was a single-pancake coil which consisted of 100
turns having the shape of a racetrack, 4.1 mm in height, with outer dimensions of
103.5 mm and 41.5 mm and inner dimensions of 75 and 12 mm [25]. The profiles of the
magnetic field component along thez-direction and thex-direction generated by the
superconducting coil magnet across itsx-axis atIDC=40 A and a distance of 10 mm
are displayed in Fig. 10.5. The maximum value of the magnetic flux density increased
with addition of iron components to the superconducting coil magnet.
Four single-pancake racetrack coils were fabricated and connected in series. They
consisted of a four-pole excitation system with a coil pitch of three times wider than
the width of the coils [26–28]. The coil form was made of paramagnetic stainless
steel with a hollow middle so that silicon steel laminations could be placed for
further testing. The thickness of the coil form was 5 mm since the width of the coated
conductor (CC) was 4.2 mm. The coils were flat and thin since each coil consisted only
ofN=10 turns with one layer of Kapton insulation tape on each subsequent turn.
The total thickness of the CC plus the insulation layer>0.2 mm. The coils had the
following dimensions: inner short radiusa 1 =19 mm, outer short radiusa 2 =21 mm,
inner long radiusc 1 =75.5 mm, outer radiusc 2 =77.5 mm, and a height 2b=4.2 mm
(Fig. 10.6a and b). A total of less than 16 m of CC wire was used for all four coils
combined including all current leads and links between adjacent coils.
The critical current (Ic) of each coil was measured beforehand. Even though a
higher standard was normally set on superconducting coils with a critical electric field
ofEc=0.1 V/cm, we set ourIctoEc=1 V/cm since each coil used only consisted of 10
turns. Then-value was determined from the slope of the logarithm of current versus
the logarithm of voltage near the critical current value. Even though direct current was
applied to the superconducting coils, we plan to use alternating current in these same
coils in the future for other experiments so their inductance was also measured and
listed in Tab. 10.3. To determine the inductance, the voltage generated by each coil was