Implementation of SST-1 plasma position control using vertical field

SST-1 (Steady State Superconducting Tokamak) is a plasma confinement device in Institute for Plasma Research (IPR) India. SST-1 has been commissioned successfully and has been carrying out plasma experiments since the beginning of 2014 and achieved a maximum plasma current of 75 kA at a central field of 1.5 T and the plasma duration ∼ 500 ms. After commissioning of first wall components SST-1 looks forward to carrying out elongated plasma experiments and stretching plasma pulses beyond 1sec. The plasma is very unstable in nature. In order to confine it for a longer duration various controls need to be act upon simultaneously. The most important control is the position control. One of the means to control plasma position is by adjusting Vertical Field (VF) which forces plasma to remain in centre of the Tokamak. The SST-1 Plasma control system is a distributed real-time system based on VME architecture. The plasma position and current are computed in real time on Digital Signal Processor (DSP) module and then transmitted to VF power supply controller over Reflective Memory (RFM) based data network where VF coil current is modified based on plasma position drift from the centre. The SST-1 recent campaign shows that real time control of VF enhanced the plasma duration by the order of few msec. This paper focuses on the architecture and implementation aspects of the plasma position feedback control system and presents the initial results observed in recent SST-1 experiment campaign. (author)