Impact of plasma diamagnetism and plasma currents on the superconducting field coils in Wendelstein 7-X

During operation of the Wendelstein 7-X stellarator, there were discharges with unusually fast plasma decay, which surprisingly triggered the quench detection system of the superconducting field coils, although no actual quench happened. We analyse the design of the field coils in conjunction with the particular technical set-up of the quench detection system and can model and quantitatively reproduce the observed behaviour. Several ways are proposed how the undesired effect could be mitigated. In addition, we discuss how the current and voltage signals of the field coils can be used in turn to derive diamagnetic energy and toroidal plasma current. ... mehrThe application is demonstrated, using signals from the existing machine control electronics, and reasonable agreement with the energy measurement of a diamagnetic loop is demonstrated

During operation of the Wendelstein 7-X stellarator, there were discharges with unusually fast plasma decay, which surprisingly triggered the quench detection system of the superconducting field coils, although no actual quench happened. We analyse the design of the field coils in conjunction with the particular technical set-up of the quench detection system and can model and quantitatively reproduce the observed behaviour. Several ways are proposed how the undesired effect could be mitigated. In addition, we discuss how the current and voltage signals of the field coils can be used in turn to derive diamagnetic energy and toroidal plasma current. ... mehrThe application is demonstrated, using signals from the existing machine control electronics, and reasonable agreement with the energy measurement of a diamagnetic loop is demonstrated.