Design and Development of Robotic Manipulator for the Measurement of Vacuum Magnetic Field Configuration in Aditya Tokamak

Abstract

Aditya tokamak is a magnetic cage to produce and contain high temperature plasma to extract nuclear fusion energy. Magnetic field coils placed around the plasma vessel generate a cage of magnetic field lines for confining the high temperature plasma. Magnetic field within the plasma volume, which is perpendicular to the plasma current act as an error field. Insufficient compensation magnetic field, imperfections in the locations of magnetic field coils, geometry of the existing coils, small variation in the coil fabrication or misalignment and stray fields are the major sources of error in magnetic field. Error in magnetic field results in various problems like, small plasma discharge with delayed breakdown, runaway generation, narrow operation window and termination of the plasma discharge. For the reason it is important to measure and compensate the error in magnetic field of a tokamak. Presently, a Hall Effect sensor is used to measure the magnetic field, which is manipulated with fixtures to keep it steady and take the readings of magnetic field. But the manual methods of measurement are found to be time consuming and less accurate. To address these problems and to automate this measurement process, three designs of manipulator have been introduced. Among the developed three designs, a design using servo motor operated single axis robot to control the linear motion and, a stepper motor based mechanism to control the rotary motion of the sensor is developed for testing purpose. After testing it within certain level of magnetic field environment, some adverse effects of magnetic field is observed on electrical motor and manipulator’s body which is made up with steel and aluminum. From the results of testing, a fourth new design is suggested which can be produced and tested for safer working, i.e. working with higher level of current and stronger magnetic fields. In the new design, the distance of motors from the plasma vessel is greater than the previously tested model, and it can be placed outside the complete machine structure to perform the same task. To avoid the effect of magnetization, aluminum can be taken as a base material to fabricate the manipulator.