THE POLO COIL, A PROTOTYPE TOKAMAK POLOIDAL FIELD-COIL, DESIGN-FEATURES AND TEST-RESULTS

A prototype tokamak poloidal field con of 3 m diameter was successfull y tested. The coil was designed to withstand typical field transients like fast ramping, plasma controlling and plasma disruptions, In order to achieve these requirements a low loss conductor was developed: The coil with its components was designed according to rules of high volt age technology. A realistic test of the magnet requires at 23 kV a cur rent of 15 kA, that means a peak power of 345 MW. Therefore, a fast sw itching circuit was used combined with an additional current lead at t he middle of the magnet winding. This allowed the performance of fast field changes with increasing or decreasing field, In one operation mo de the coil was discharged into a dump resistor. In another operation mode, only one coil half is discharged which generated a field increas e in the second short circuited half of the coil. Discharging time con stants of 1 ms and local field sweep rates of about 240 T/s were obtai ned without quench. A reproducible and sharp quench boundary was found . The results showed clearly that ramp rate limitations are only given by the expected stability limit or the load line boundary.