Massimiliano Mattei

Principal physics developments evaluated in the ITER design review

As part of the ITER Design Review and in response to the issues identified by the Science and Technology Advisory Committee, the ITER physics requirements were reviewed and as appropriate updated. The focus of this paper will be on recent work affecting the ITER design with special emphasis on topics affecting near-term procurement arrangements. This paper will describe results on: design sensitivity studies, poloidal field coil requirements, vertical stability, effect of toroidal field ripple on thermal confinement, material choice and heat load requirements for plasma-facing components, edge localized modes control, resistive wall mode control, disruptions and disruption mitigation.

Plasma response models for current, shape and position control in JET

Abstract This paper presents the features and the performance of the Joint European Torus (JET) plasma response models based on an upgraded version of the CREATE-L code. It takes into account a number of aspects, including an equivalent axisymmetric model of the iron core and the eddy currents induced in the passive structures. The input quantities are the poloidal field circuit currents (or voltages) and two parameters related to the plasma current density profile. The output quantities include the signals provided by the magnetic diagnostic system of JET (fields, fluxes and flux differences) as well as plasma current and shape. The equivalent axisymmetric model of JET and the plasma response models have been assessed on a set of JET pulses, by comparing the simulated open loop response of the magnetic measurements and the plasma shape to the experimental measurements. The electromagnetic analysis shows that the axisymmetric model of the iron is satisfactory. The linearized plasma response model provides a reliable base for the design and the assessment of a new current, shape and position control system in JET, and accurately predicts the growth rate of the vertical instability of an elongated JET plasma.

Development of ITER 15 MA ELMy H-mode inductive scenario

The poloidal field (PF) coil system on ITER, which provides both feedforward and feedback control of plasma position, shape, and current, is a critical element for achieving mission performance. Analysis of PF capabilities has focused on the 15 MA Q = 10 scenario with a 300-500 s flattop burn phase. The operating space available for the 15 MA ELMy H-mode plasma discharges in ITER and upgrades to the PF coils or associated systems to establish confidence that ITER mission objectives can be reached have been identified. Time dependent self-consistent free-boundary calculations were performed to examine the impact of plasma variability, discharge programming, and plasma disturbances. Based on these calculations a new reference scenario was developed based upon a large bore initial plasma, early divertor transition, low level heating in L-mode, and a late H-mode onset. Equilibrium analyses for this scenario indicate that the original PF coil limitations do not allow low li (<0.8) operation or lower flux states, and the flattop burn durations were predicted to be less than the desired 400 s. This finding motivates the expansion of the operating space, considering several upgrade options to the PF coils. Analysis was also carried out to examine the feedback current reserve required in the CS and PF coils during a series of disturbances and a feasibility assessment of the 17 MA scenario was undertaken. Results of the studies show that the new scenario and modified PF system will allow a wide range of 15 MA 300-500 s operation and more limited but finite 17 MA operation.

Passive and active mass damper control of the response of tall buildings to wind gustiness

Abstract The performance of passive (TMD), active (AMD) and hybrid (ATMD) mass dampers for the reduction of the buffeting response of tall buildings is investigated. First a simple 1+1 DoF system is considered to model the main structure provided with a mass damper, and the wind buffeting force is simplified into a white noise excitation. A linear quadratic regulator (LQR) control law is used, and in the case of the ATMD, the results are compared to those obtained with a closed form design procedure from the literature. Second a 64-storey building is considered, and modelled accounting for its first four longitudinal modes. In the latter case a more realistic buffeting excitation is considered, accounting for the frequency distribution of the atmospheric turbulence, and for its vertical correlation. It is pointed out how the performance of each device is strongly related to the response parameter to be mitigated, and how simplified 1+1 DoF models can inaccurately estimate the system response, and therefore the control performance.

Experimental studies of ITER demonstration discharges

Key parts of the ITER scenarios are determined by the capability of the proposed poloidal field (PF) coil set. They include the plasma breakdown at low loop voltage, the current rise phase, the performance during the flat top (FT) phase and a ramp down of the plasma. The ITER discharge evolution has been verified in dedicated experiments. New data are obtained from C-Mod, ASDEX Upgrade, DIII-D, JT-60U and JET. Results show that breakdown for Eaxis < 0.23–0.33 V m−1 is possible unassisted (ohmic) for large devices like JET and attainable in devices with a capability of using ECRH assist. For the current ramp up, good control of the plasma inductance is obtained using a full bore plasma shape with early X-point formation. This allows optimization of the flux usage from the PF set. Additional heating keeps li(3) < 0.85 during the ramp up to q95 = 3. A rise phase with an H-mode transition is capable of achieving li(3) < 0.7 at the start of the FT. Operation of the H-mode reference scenario at q95 ~ 3 and the hybrid scenario at q95 = 4–4.5 during the FT phase is documented, providing data for the li (3) evolution after the H-mode transition and the li (3) evolution after a back-transition to L-mode. During the ITER ramp down it is important to remain diverted and to reduce the elongation. The inductance could be kept ≤1.2 during the first half of the current decay, using a slow Ip ramp down, but still consuming flux from the transformer. Alternatively, the discharges can be kept in H-mode during most of the ramp down, requiring significant amounts of additional heating.

Observer-based sensor fault detection and isolation for chemical batch reactors

In this paper a scheme for detection and isolation of sensor faults in chemical batch reactors is proposed. The scheme is based on a bank of two observers for residual generation which guarantees sensor fault detection and isolation in presence of external disturbances and model uncertainties. In the observers a Hog approach is adopted for the design of the gains, while the unknown dynamics of the reactor (i.e., the heat released by the reaction) are estimated by an on-line interpolator based on a radial basis functions (RBF) neural network. Finally, the estimates provided by the observers and the sensor measures are processed by a decision making system (DMS) that provides information about the faulty sensor and an healthy measure. In order to test the effectiveness of the proposed approach, a simulation case study is developed

Smooth Flight Trajectory Planning in the Presence of No-Fly Zones and Obstacles

This paper describes a novel procedure to generate continuously differentiable optimal flight trajectories in the presence of arbitrarily shaped no-fly zones and obstacles having a fixed position in time. The operational flight scenario is first discretized with a finite dimensional grid of positions-directions pairs. A weighted and oriented graph is then defined for which the nodes are the earlier mentioned grid points and for which the arcs correspond to minimum length trajectories compliant with obstacle avoidance constraints. Arcs are obtained via solving convex quadratic programming optimization problems that can also account for geometrical constraints such as trajectory curvature limitations. The problem of finding an optimal trajectory be tween two nodes of the so-called core paths graph is then solved via a minimum cost path search algorithm. In a real-time application perspective, the generation of the core paths graph is computationally cumbersome. Moreover, the aircraft position and direction rarely coincide with one of the graph nodes. However, if the graph is built offline and stored, the definition of an optimal trajectory connecting any points of the space domain requires a reduced computational effort. The particular case of piecewise polynomial trajectories minimizing a flight paths length, compliant with constraints on curvature and flight-path angles, is fully developed. Two- and three-dimensional examples are discussed to show the applicability as well as the effectiveness of the technique.

A note on quadratic stability of uncertain linear discrete-time systems

In this paper we consider a linear discrete-time system depending on a vector of uncertain parameters. Assuming that the system matrix depends on parameters as the ratio of a multiaffine matrix-valued function and a multiaffine polynomial and that the parameters range in a hyper-rectangle, we show that the uncertain system is quadratically stable if and and only if the set of vertex systems is quadratically stable. This allows us to state a necessary and sufficient condition for quadratic stability in terms of the solvability of a feasibility problem involving linear matrix inequalities.

Brief Guaranteeing cost strategies for linear quadratic differential games under uncertain dynamics

This paper deals with the design of closed loop strategies for a class of two player zero-sum linear quadratic differential games, where the state equation is affected by uncertainties in the so-called norm bounded, one-block form. The proposed strategies guarantee to each player a given performance and, to be evaluated, require the solution of two scaled Riccati differential equations.

Self-consistent simulation of plasma scenarios for ITER using a combination of 1.5D transport codes and free-boundary equilibrium codes

Self-consistent transport simulation of ITER scenarios is a very important tool for the exploration of the operational space and for scenario optimization. It also provides an assessment of the compatibility of developed scenarios (which include fast transient events) with machine constraints, in particular with the poloidal field coil system, heating and current drive, fuelling and particle and energy exhaust systems. This paper discusses results of predictive modelling of all reference ITER scenarios and variants using two suites of linked transport and equilibrium codes. The first suite consisting of the 1.5D core/2D SOL code JINTRAC (Wiesen S. et al 2008 JINTRAC-JET modelling suite JET ITC-Report) and the free-boundary equilibrium evolution code CREATE-NL (Albanese R. et al 2003 ISEM 2003 (Versailles, France); Albanese R. et al 2004 Nucl. Fusion 44 999), was mainly used to simulate the inductive D-T reference Scenario-2 with fusion gain Q = 10 and its variants in H, D and He (including ITER scenarios with reduced current and toroidal field). The second suite of codes was used mainly for the modelling of hybrid and steady-state ITER scenarios. It combines the 1.5D core transport code CRONOS (Artaud J.F. et al 2010 Nucl. Fusion 50 043001) and the free-boundary equilibrium evolution code DINA-CH (Kim S.H. et al 2009 Plasma Phys. Control. Fusion 51 105007).