Aum Raval, BS (Honours) in Physics, Class of 2024

Supervisor: Professor Raghwinder Singh, School of Arts and Sciences

Thesis Brief

The measurement of plasma current is one of the critical parameters in characterising plasma and understanding its behaviour. Conventionally, the Rogowski coil is used to measure plasma current. The problem with this approach arises when long, steady-state plasma shots are conducted. Due to the usage of integrators, drift is generated in the output signal. A diagnostic system, Magneto-Optic Current Sensor (MOCS), has been developed and commissioned on the Aditya-Upgrade tokamak for plasma current measurements. The MOCS is an optical diagnostic technique based on the Faraday rotation effect within a single-mode optical fibre (SMF), offering a supplementary measurement approach to the conventional Rogowski coil method. This technique possesses advantages over traditional current measurement techniques, leading to a potential measurement diagnostic tool for future fusion devices and steady-state tokamak devices.

In this project, an investigation is to be made on the axial twisting of the optical fibre to suppress its linear birefringence. In the lab, a systematic study will be made to study the effect of the number of axial twists introduced in the optical fibre and the corresponding possible improvement in the linear birefringence of the SMF having different lengths. Characterisation of the Verdet constant in the lab to evaluate the sensitivity of the MOCS diagnostic setup. Following the lab characterisation, the application of the new setup to the Plasma current measurements on the Aditya-U tokamak is to be done. Additionally, an improvement in the data analysis algorithm has been carried out. It is expected that the twisted SMF will improve the plasma current measurements compared to the SMF without twists.