Jean-François Artaud

Lyapunov-based distributed control of the safety-factor profile in a tokamak plasma

A real-time model-based controller is developed for the tracking of the distributed safety-factor profile in a tokamak plasma. Using relevant physical models and simplifying assumptions, theoretical stability and robustness guarantees were obtained using a Lyapunov function. This approach considers the couplings between the poloidal flux diffusion equation, the time-varying temperature profiles and an independent total plasma current control. The actuator chosen for the safety-factor profile tracking is the lower hybrid current drive, although the results presented can be easily extended to any non-inductive current source. The performance and robustness of the proposed control law is evaluated with a physics-oriented simulation code on Tore Supra experimental test cases.

Plasma Discharge Management for Long-Pulse Tokamak Operation

Abstract Achieving high-performance long-duration plasma discharges in tokamaks is one of the most important challenges to be addressed in the perspective of the development of a power plant. For this purpose, real-time handling of off-normal events has to be performed through a dedicated plasma discharge management system. In this paper, we describe the main requirements and features of such a system. A generic architecture, based on the principle of subsidiarity, is proposed. A full set of actions is covered, starting from the local subsystems up to the tokamak as a whole, with different levels of mitigation strategies. A simulation of a relevant test case, based on the Tore Supra tokamak, showing the basic principles of the study, is also presented.

Coupling between a multi-physics workflow engine and an optimization framework

A generic coupling method between a multi-physics workflow engine and an optimization framework is presented in this paper. The coupling architecture has been developed in order to preserve the integrity of the two frameworks. The objective is to provide the possibility to replace a framework, a workflow or an optimizer by another one without changing the whole coupling procedure or modifying the main content in each framework. The coupling is achieved by using a socket-based communication library for exchanging data between the two frameworks. Among a number of algorithms provided by optimization frameworks, Genetic Algorithms (GAs) have demonstrated their efficiency on single and multiple criteria optimization. Additionally to their robustness, GAs can handle non-valid data which may appear during the optimization. Consequently GAs work on most general cases. A parallelized framework has been developed to reduce the time spent for optimizations and evaluation of large samples. A test has shown a good scaling efficiency of this parallelized framework. This coupling method has been applied to the case of SYCOMORE (System COde for MOdeling tokamak REactor) which is a system code developed in form of a modular workflow for designing magnetic fusion reactors. The coupling of SYCOMORE with the optimization platform URANIE enables design optimization along various figures of merit and constraints

Development of long pulse RF heating and current drive for H-mode scenarios with metallic walls in WEST

The longstanding expertise of the Tore Supra team in long pulse heating and current drive with radiofrequency (RF) systems will now be exploited in the WEST device (tungsten-W Environment in Steady-state Tokamak) [1]. WEST will allow an integrated long pulse tokamak programme for testing W-divertor components at ITER-relevant heat flux (10-20 MW/m2), while treating crucial aspects for ITER-operation, such as avoidance of W-accumulation in long discharges, monitoring and control of heat fluxes on the metallic plasma facing components (PFCs) and coupling of RF waves in H-mode plasmas. Scenario modelling using the METIS-code shows that ITER-relevant heat fluxes are compatible with the sustainment of long pulse H-mode discharges, at high power (up to 15 MW / 30 s at IP = 0.8 MA) or high fluence (up to 10 MW / 1000 s at IP = 0.6 MA) [2], all based on RF heating and current drive using Ion Cyclotron Resonance Heating (ICRH) and Lower Hybrid Current Drive (LHCD). This paper gives a description of the ICRH and LH...

The new magnetic diagnostics in the WEST tokamak

The WEST tokamak consists of a major upgrade of the superconducting medium size tokamak Tore Supra aiming at testing ITER divertor components. Such modification has required rebuilding a full set of magnetic diagnostics. The project was started in 2013 and completed in 2016. The diagnostic consists of a set of 469 sensors (421 pick-up coils, 36 flux loops, and 12 Rogowski coils) installed in the WEST vacuum vessel. New analog integrators have been developed in order to obtain the magnetic field and flux from the raw signal of the sensors. During the startup phase of WEST, plasma currents of the order of a few kilo amperes were measured despite much larger current of the order of hundreds of kilo amperes flowing in nearby conducting structures. The diagnostic is now fully operational and exhibits a noise level of about 0.5 mT on the magnetic field, and 2.0 mWb on flux loops allowing identifying the plasma boundary with an accuracy of a few millimeters on a 2 ms time cycle.

A Finite Element Versus Analytical Approach to the Solution of the Current Diffusion Equation in Tokamaks

This paper deals with two efficient approaches for solving the current diffusion equation (CDE), which governs current diffusion through the conductive plasma inside a tokamak and compares them to CRONOS tokamak simulation suite, as well. Namely, CDE is solved via the finite-element method (FEM) and an analytical technique, respectively, and the obtained results are subsequently compared with the solution obtained from the state-of-the-art CRONOS suite with finite-difference calculations. The FEM solution is carried out featuring the use of linear and Hermite type shape functions, respectively, while the analytical solution is obtained by applying certain approximations to the CDE. The tradeoff between different approaches has been undertaken. Thus, the results obtained via the FEM approach (with Hermite basis function, in particular) show very good agreement with the CRONOS results, while also providing the stability of the solution. On the other hand, the results obtained via the analytical solution clearly demonstrate a good agreement with the numerical results in the edge region, which makes it very useful for various applications, e.g., for benchmarking purposes.