Real-time control of theq-profile in JET for steady state advanced tokamak operation

Abstract

In order to simultaneously control the current and pressure profiles in high performance tokamak plasmas with internal transport barriers (ITB), a multi-variable model-based technique has been proposed. New algorithms using a truncated singular value decomposition (TSVD) of a linearised model operator and retaining the distributed nature of the system have been implemented in the JET control system. Their simplest versions have been applied to the control of the current density profile in reversed shear plasmas using three heating and current drive actuators (neutral beam injection, ion cyclotron resonant frequency heating and lower hybrid current drive). Successful control of the safety factor profile has been achieved in quasi steady state, on a time scale of the order of the current redistribution time. How the TSVD algorithm will be used in the forthcoming campaigns for the simultaneous control of the current profile and of the ITB temperature gradient is discussed in some detail, but this was not yet attempted in the present pioneering experiments.

Diagnostics and control for the steady state and pulsed tokamak DEMO

“…Demonstrative experiments of the q-profile control were done on a JET using heating systems as actuators and interferometry/polarimetry as sensors [57,58] used for the reconstruction of the equilibrium in real time.…”

Dynamic optimization of open-loop input signals for ramp-up current profiles in tokamak plasmas

“…The problem of manipulating the current profile to achieve high performance while satisfying safety requirements has attracted considerable attention in the literature. The pioneering work in this area is due to Moreau, who in [15] derived empirical models for current profile evolutions using system identification techniques, and then used these models to synthesize a controller for safety factor profile manipulation. This approach, called the data-driven modeling method, does not rely on first principles to derive the model, but rather involves constructing the model by fitting observed data from experiments (e.g., JT-60 in Japan and DIII-D in the USA [16]), where the observed data is generated by input signals covering a sufficiently broad range of frequencies.…”

Integrated scenario in JET using real-time profile control

“…Although the detailed conditions for the creation of Internal Transport Barriers (ITBs) are still uncertain [13], the aim of these tools is to improve the stability and reliability of this mode of operation by the control of current and pressure profile simultaneously [11]. In real discharges, small deviations from the reference scenario may indeed increase with time.…”

“…for s=0). [11]. From this analysis, it is possible to invert the truncated diagonal matrix S (0), and obtain a feedback control with a controller transfer function of the form:…”

“…This confirms that in ITER a very large effort will be devoted to the development of real time control tools. Among the recent tools developed in JET, the real time equilibrium, together with real time electron and ion temperature and current profiles measurements, has dramatically enhanced the experimental work on the integration of advanced tokamak scenario and in particular the development of the techniques to control in real time the q and pressure profiles simultaneously [11]. This paper reports the technical and scientific achievements made in JET in this domain.…”