Recent developments in ITER magnetic control algorithms

Axi-symmetric magnetic control functions are an important part of the ITER Plasma Control System (PCS) which is now at an advanced design stage. They are aimed at plasma current control, plasma shape control, and vertical stabilization. In principle, these control actions could be decoupled using different sets of active CS/PF coils as in many existing tokamaks. However, in large tokamaks with superconducting coils the controller design becomes more challenging given the high level of coupling among control circuits, the long control fields penetration time, and the use of the same actuators for different control purposes (the so-called actuator sharing). The objective of this paper is to make evidence of ITER PCS flexibility with an illustration of the architecture of the axi-symmetric magnetic control. Important features are (i) the capability to implement both a current-driven and a voltage-driven control scheme, (ii) the capability of controlling the plasma current either at the shape control level or at the circuit current control level, (iii) the concurrent use of both in-vessel and ex-vessel coils to tackle the vertical stabilization problem, (iv) and the capability to manage coil current limits and other exceptions in real-time. To guarantee satisfactory performance over all the operating envelope, a scheduling of the controller parameters is implemented at the control functions level, whereas a magnetic control local supervisor is in charge of the interface with the higher level supervisor, as well as of control algorithms selection. The design is carried out according to the general philosophy of the PCS design including also test assessments on the PCSSP platform.