Concepts and challenges in the design of a tokamak plasma control system. ITER PCS for First Plasma and beyond

Electricity production through the control of nuclear fusion reactions is a promising option to meet the increasing demand for clean energy sources. The magnetically confined approach based on the tokamak is presently investigated through the international ITER project. ITER is the largest fusion development project aimed at demonstrating the capability of generating 500MW of fusion power with an input of 50MW (Q=10) for long durations (> 5 min) by controlling fusion reactions. The project requires a multidisciplinary development approach from materials to cooling system and, of course, control. The high temperature plasmas generated in a tokamak require continuous control to guarantee the achievement and sustainment of the required performance to demonstrate a high fusion energy gain. This requires an integrated set of controls with multiple inputs and multiple outputs, sharing the available actuators supported by an effective system to avoid, where possible, conditions that could ultimately, compromise the integrity of the device. This role is in the scope of the Plasma Control System (PCS). A lot of experience has been already gained from present fusion devices, but the scale of ITER and future reactors requires further developments in the field. The control in ITER is similar to other devices, but more complexity is required by the new physics to be explored in ITER scenarios, the robustness against larger loads (e.g. high neutron flux rate) and the systematic application of multiple controls sharing resources or by narrow operational spaces/proximity to instability boundaries associated with high Q operation. Moreover, the design of the PCS requires a model-based approach, considering that the machine for which it is designed is under construction. On the other hand, while the control schemes will be validated through simulations ahead of operation, the PCS will only be fully tested and commissioned through ITER operation itself. In this paper, an overview of a PCS and its design is presented followed by recent development targeting the ITER PCS for First Plasma and future operations. Constraints, limitations and challenges will be illustrated and the adopted solutions presented.