Real time control developments at JET in preparation for deuterium-tritium operation

Content Robust high performance plasma scenarios are being developed to exploit the unique capability of JET to operate with Tritium and Deuterium. In this context, real time control schemes are used to guide the plasma into the desired state and maintain it there. Other real time schemes detect undesirable behaviour and trigger appropriate actions to assure the best experimental results without unnecessary use of the limited neutron production and Tritium budget. Rather than discussing the traditional plasma position, current and density control systems, this paper will concentrate on more advanced control schemes which are in use or under development at JET. Such controllers fall naturally into two categories: 1: Continuously active controllers, exemplified by the control of Beta via NBI as developed in the 1990s, use various diagnostics together with real time processing to generate actuator requests aimed at maintaining the plasma in the desired state. More recent successful advances include: (i) Control of the degree of plasma detachment via impurity injection; (ii) ELM frequency control via gas/Pellet injection; (iii) Sawtooth pacing using ICRH modulation. 2: Event/threshold detection algorithms triggering a variety of actions: (i) Execute the safest possible termination strategy if the plasma is heading towards a disruption. Different actions, such as reduction of plasma current or the triggering of massive gas injection for disruption mitigation, are executed depending on whether the disruption is imminent or not. (ii) Terminate pulses early, when they do not seem likely to produce the desired plasma conditions. This would save neutron and tritium budget allowing an increased number of successful discharges to be run. Before going into Deuterium-Tritium operation these control schemes should be integrated into the plasma scenarios, assuring that the various controllers are mutually compatible. Work to assure this integration will be of high priority for JET in the next experimental campaign.