Plasma Vertical Velocity Measurement from Unintegrated Magnetic Signals

Due to the vertical instability of an elongated plasma, it is necessary to provide an active feedback system to control the plasma's vertical position. Modern magnetic diagnostics, which require integration to calculate the magnetic field, are insufficient for future devices with long run-times due to the integration drift introducing a non-negligible error. This work explores the possibility of using the unintegrated signals from Mirnov coils to directly calculate the vertical velocity of the plasma, which can be used in a feedback control system that partially suppresses the growth of the vertical instability. A code has been developed to perform this calculation in real-time. The effects of vessel wall eddy currents are taken into account in the calculation. By delegating the fast response portion of the vertical stability control problem to unintegrated magnetic signals, the plasma position can be controlled on a longer timescale using slower diagnostics, such as a camera, that can circumvent the integration drift issue.