PCB Rogowski Sensor Designs for Plasma Current Measurement

The Rogowski coil is very useful in transient current measurement. A Rogowski sensor consisting of a Rogowski coil and an integrator is one of the most important diagnostic instrumentations in a Tokamak. In recent years, new structures of the Rogowski coil based on a printed circuit board are developed to replace the traditional handmade Rogowski coil for more excellent accuracy, better temperature stability, more accordant mutual-inductance, more symmetrical windings and other advantages. However, the existing structures of the Rogowski coil based on a PCB are useless in a Tokamak because the required Rogowski coil installed on the vacuum vessel should have large diameter and little volume. This presentation provides a new twin-loops Rogowski coil (TRC) consisting of several PCB strips. The TRC has all the advantages of existing PCB Rogowski coils and can meet the limited space requirement in a Tokamak at the same time. A special experiment is carried out to prove that the mutual-inductance of TRC is immune to the variation of center position of plasma current. Moreover, a differential long-term integrator is designed to cooperate with the TRC. Two switches are used in the integrator to release the remaining electric charges on integrating capacitors once the measurement is over. Then, the error accumulation of integrator is canceled in repetitious measurements. The designed new Rogowski sensor can be used to measure long pulse current below 1 second.