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Abstract: Sensitivity studies performed as part of the ITER IO design review highlighted a very stiff dependence of the maximum Q attainable on the machine parameters. In particular, in the considered range, the achievable Q scales with I p ^4. As a consequence, the achievement of the ITER objective of Q =10 requires the machine to be routinely operated at a nominal current I p of 15MA, and at full toroidal field BT of 5.3T. This paper analyses the capabilities of the poloidal field (PF) system (including the central solenoid) of ITER against realistic full current plasma scenarios. An exploration of the ITER operational space for the 15 and 17MA inductive scenario is carried out. An extensive analysis includes the evaluation of margins for the closed loop shape control action. The overall results of this analysis indicate that the control of a 15MA plasma in ITER is likely to be adequate in the range of li 0.7–0.9 whereas, for a 17MA plasma, control capabilities are strongly reduced. The ITER operational space, provided by the reference pre-2008 PF system, was rather limited if compared to the range of parameters normally observed in present experiment. Proposals for increasing the current and field limits on PF2, PF5 and PF6, adjustment on the number of turns in some of the PF coils, changes to the divertor dome geometry, to the conductor of PF6 to Nb3Sn, moving PF6 radially and/or vertically are described and evaluated in the paper. Some of them have been included in 2008 ITER revised configuration. [Copyright &y& Elsevier]

The Plasma Control System (PCS) is in charge of robustly controlling the evolution of plasma parameters against model uncertainties and disturbances, with the aim of achieving the envisaged goals and performance. The PCS design process follows a System-Engineering approach to support all the design phases, from control algorithms specifications to the verification and validation tests for various components. A case study concerning the design of the Correction Coils Current Controllers is presented in this paper. The aim is to show on a smaller scale the approach that is applied to the entire design of the PCS, by highlighting its effectiveness, from the refinement of the requirements, up to their validation in the simulation environment. [ABSTRACT FROM AUTHOR]

Abstract: As the ITER project moves forward in the procurement phase of major components, the baseline design is subject to a series of modifications due to the finalization of the design and interaction with industry. Some modifications have a potential impact on the performance and operation of the machine. A substantial activity is being carried out in EU in support to the design, aimed at assessing such impact. The effect of the 2010 design of the central solenoid on the operational space was assessed. A detailed analysis of the plasma breakdown and start-up phases was performed to assess the impact of withdrawing the booster converters from the baseline design and of the modifications to the power supply voltage ratings. In order to reach a clear conclusion, a review of the start-up strategy was also carried out starting from an analysis of the avalanche and breakdown conditions in ITER. The controllability of the null quality and position was verified in presence of uncertainties and measurement errors. The advantages of higher voltage rating were also quantified. General aim of the paper is to present an overview of the analyses performed and of the issues identified providing an assessment of the impact of some of the proposed changes on ITER operation. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

• Assessment of the plasma shape control for JT60-SA through a selection of an optimal set of gaps. • Approach based on the eXtreme Shape Controller (XSC) permits to control a number of gaps lager than the number of poloidal field coils. • Selection of other configurations for the set of gaps revealed a greater RMSE value. This paper deals with the plasma shape control problem in JT-60SA. An assessment of the plasma shape control performance is presented, aimed at the definition of an optimal set of gaps to be controlled. Indeed, JT-60SA represents a relevant benchmark to further validate this control approach given the high beta regimes that are envisaged during its operation. Moreover, such regimes represent a challenge from the plasma magnetic control perspective. The control approach considered for the assessment is based on the eXtreme Shape Controller (XSC), since such an approach permits to control, in a least mean square sense, a number of shape descriptors that is larger than the number of poloidal field coils. Considering that the design of the XSC is model-based , the CREATE linear model for the plasma-circuit response has been used for the design. In the presented analysis, the capability of tracking different plasma shapes, as well as the one of rejecting disturbances has been considered. The result of this analysis suggests that a set of about 20 gaps equally spaced along the plasma boundary permits to control the shape with a steady-state root-mean square error of less than 1 cm during the flattop of JT-60SA Scenario 2, in the presence of a set of relevant disturbances. [ABSTRACT FROM AUTHOR]

• Preliminary results on the magnetic control of the plasma shape on DEMO. • Current, position and shape control performed at the same time. • Controller performance tested in the presence of an H-L transition. About 85% of the primary energy is currently obtained from fossil sources. In the next future, nuclear fusion can significantly contribute to energy production: the fuel is in principle unlimited and radioactive waste are short lived. Next steps in fusion research are represented by the two tokamaks ITER, which is under construction, and DEMO, which is in its conceptual design phase. In this paper we focus on a specific aspect of DEMO design, that is indeed crucial for tokamak safe operation: plasma vertical and shape control. It is well known that a plasma with elongated cross-section exhibits a vertical instability that needs to be feedback controlled. Typically on operating tokamaks, and in ITER, this task is accomplished using in-vessel actuator coils. Since in the present DEMO design these coils are not foreseen, hereafter we assumed that all the actuator coils, located outside the vessel, are used at the same time to guarantee both vertical stabilization and shape control, resorting to a suitable geometric decoupling. The performance of the controller is shown in simulation using a nonlinear evolution code during a plasma H-L back-transition. [ABSTRACT FROM AUTHOR]

The Plasma Control System Simulation Platform (PCSSP) is a highly flexible, modular, time-dependent simulation environment developed primarily to support development of the ITER Plasma Control System (PCS). It has been under development since 2011 and is scheduled for first release to users in the ITER Organization (IO) and at selected additional sites in 2015. Modules presently implemented in PCSSP enable exploration of axisymmetric evolution and control, basic kinetic control, and tearing mode suppression. A basic capability for generation of control-relevant events is included, enabling study of exception handling in the PCS, continuous controllers, and PCS architecture. While the control design focus of PCSSP applications tends to require only a moderate level of accuracy and complexity in modules, more complex codes can be embedded or connected to access higher accuracy if needed. This paper describes the background and motivation for PCSSP, provides an overview of the capabilities, architecture, and features of PCSSP, and discusses details of the PCSSP vision and its intended goals and application. Completed work, including architectural design, prototype implementation, reference documents, and IO demonstration of PCSSP, is summarized and example use of PCSSP is illustrated. Near-term high-level objectives are summarized and include preparation for release of an “alpha” version of PCSSP and preparation for the next development phase. High-level objectives for future work are also discussed. [ABSTRACT FROM AUTHOR]

This paper gives an overview of the scope and context of the CODAC high-level real-time applications (Supervision and Plasma Control) and presents the strategy and current state of design of the tools to support the implementation. A real-time framework, which is currently under development with strong support of the worldwide fusion community will not only support the implementation of plasma control strategies with the extensive exception handling and forecasting functionality foreseen for ITER, but also integrated commissioning, orchestration and supervision as well as the real-time needs of ITER plant system developers. A second cornerstone in the implementation strategy is the development of a powerful simulation environment (Plasma Control System Simulation Platform – PCSSP) to design and verify control strategies, event handling and orchestration and automation. The development of PCSSP is currently under contract and this paper will also give an overview of its current state of development. [ABSTRACT FROM AUTHOR]

The plasma design point during stationary phase operation of EU-DEMO has been described extensively in the past, and the assumptions employed for its definition have been supported by various investigations. However, a stationary snapshot is by far not sufficient to ensure the actual operability of the plasma scenario. On the contrary, both normal and off-normal transients have a strong impact on the machine design, providing the most challenging requirements to the actuators. This has to be accounted for in the design from the early phases on. In this paper, the main requirements originating from plasma operation, studied during the Pre-Concept Design Phase, are briefly reviewed. These encompass the so-called planned transients, e.g. plasma current ramps, access and termination of the burn phase or plasma fueling with pellets, but also the mitigation of off-normal events which may lead to a disruption, e.g. the divertor reattachment or an uncontrolled increase of radiation after a sudden W influx from the wall. [ABSTRACT FROM AUTHOR]

In view of the preparation for the operation of the ITER tokamak it is necessary to develop the plasma scenarios taking into account all engineering constraints coming from the plant and including a realistic control system. It is important to consider that, due to the high energy of ITER plasmas, much more stringent requirements are posed on the control of transients in order to avoid machine damage. Several activities are performed in the EU focusing on one side on the scenario optimization from a physics point of view and on the other side on the design and modeling of a realistic plasma control system driving the plasma configuration throughout the whole pulse and suitable for implementation on a real machine. The issues related to the computation of the control feed-forward component are addressed. In particular, the possibility to trigger a feed-forward component to solve controllability problems arising in the transitions from plasma L to H and H to L modes is studied in detail with the support of linear and non-linear simulations. A control strategy is designed and tested on non-linear simulations of the whole pulse, including linear and non-linear effects due to controller switching, plasma shape reconstruction and power supplies. The paper reports on the results of the studies performed and discuss the proposed design of the plasma control system. [ABSTRACT FROM AUTHOR]

Abstract: ITER is targeting Q =10 with 500MW of fusion power. To meet this target, the plasma needs to be controlled and shaped for a period of hundreds of seconds, avoiding contact with internal components, and acting against instabilities that could result in the loss of control of the plasma and in its disruptive termination. Axisymmetric magnetic control is a well-understood area being the basic control for any tokamak device. ITER adds more stringent constraints to the control primarily due to machine protection and engineering limits. The limits on the actuators by means of the maximum current and voltage at the coils and the few hundred ms time response of the vacuum vessel requires optimization of the control strategies and the validation of the capabilities of the machine in controlling the designed scenarios. Scenarios have been optimized with realistic control strategies able to guarantee robust control against plasma behavior and engineering limits due to recent changes in the ITER design. Technological issues such as performance changes associated with the optimization of the final design of the central solenoid, control of fast transitions like H to L mode to avoid plasma-wall contact, and optimization of the plasma ramp-down have been modeled to demonstrate the successful operability of ITER and compatibility with the latest refinements in the magnetic system design. Validation and optimization of the scenarios refining the operational space available for ITER and associated control strategies will be proposed. The present capabilities of magnetic control will be assessed and the remaining critical aspects that still need to be refined will be presented. The paper will also demonstrate the capabilities of the diagnostic system for magnetic control as a basic element for control. In fact, the noisy environment (affecting primarily vertical stability), the non-axisymmetric elements in the machine structure (affecting the accuracy of the identification of the plasma boundary), and the strong component of eddy current at the start-up (resulting in a poor S/N ratio for plasma reconstruction for I p <2MA requiring a robust plasma control) make the ITER magnetic diagnostic system a demanding part of the magnetic control and investment protection systems. Finally the paper will illustrate the identified roles of magnetic control in the PCS (plasma control system) as formally defined in the recent first step of the design and development of the system. [Copyright &y& Elsevier]

Abstract: The plasma control system simulation platform (PCSSP) for ITER shall support the analysis and development of methods to be used by the ITER plasma control system (PCS) for handling exceptions to optimize pulses and assist in machine protection. PCSSP will permit to investigate physical and technical events, such as component failures, control degradation, operation domain excess, plasma state bifurcation or instabilities, and interlock activity. Serving that purpose, the plasma, actuator, diagnostics and PCS simulation modules in PCSSP will be enhanced to compute nominal and off-normal data. Configured by an event schedule, an event generator will orchestrate the activation and manipulate the characteristics of such off-normal computation. In the simulated PCS exceptions will be handled in a pulse supervision layer operating on top of the pulse continuous control (PCC) feedback loops. It will monitor events, decide on which exceptions to respond, and compute new control references to modify PCC behavior. We discuss basic concepts for the event generation in PCSSP, and a preliminary architecture for exception handling in PCS, and show how these will be configured with event and pulse schedules. [Copyright &y& Elsevier]

Highlights: [•] Describes task to develop simulation tool to aid development/testing of ITER PCS. [•] Requirements and use cases and preliminary architecture have been delivered. [•] Detailed design is now being developed. [•] Provides overview of use cases and requirements. [•] Provides overview of architecture and status of development. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the PFX Operating Early Task (POET) was to obtain a highly shaped plasma and x-point formation in the early phases of the discharge. The PFX is an amplifier which feeds the central pancakes of the JET primary circuit. In the past it was possible to energize the PFX circuit only when the PFGC current, which feeds all the coils of the primary circuit, was already flowing in the same direction as the PFX current would have flowed, to avoid repulsive vertical forces which would tend to lift the top pancakes of the central solenoid, balanced only by the net weight of the upper part of the JET machine. In this paper the modeling activity performed to provide a more accurate estimate of the ejection forces acting on the upper coils in order to safely widen the operational space, by using two dimensional finite element electromagnetic models and the simulation of the performances of the actual controller algorithm on tracking the desired references of current are described. Finally will be presented the results of the implemented POET system, routinely used in JET in the 2011/2012 experimental campaigns, in terms of anticipation of x-point formation and enhanced system flexibility. [Copyright &y& Elsevier]

Abstract: The JET enhancement project Plasma Control Upgrade (PCU) aimed at increasing the capabilities of the plasma vertical stabilization (VS) system. One of the activities of this project was devoted to the development of simple but sufficiently accurate models of the VS system so as to address the main design choices, use the simulation tools as reliable test-beds, and provide an adequate support to the engineering design and commissioning of the new Enhanced Radial Field Amplifier (ERFA). This paper illustrates some of the main achievements of the modelling activity, which gave rise to a closed loop model of the VS system, including plasma, PF coils and passive structures. In particular the paper deals with the selection of the set of turns to be used in the control coils and with the estimation of the eddy current effects on the VS system. The latter analysis addressed an upgrade of the converter units of ERFA, successfully implemented during its commissioning on plasma in August 2009. [Copyright &y& Elsevier]

Abstract: In the framework of the ITER project, an investigation has been conducted on an alternative vessel and blanket design, aimed at reducing cost and production risk. The modifications proposed have a strong impact on plasma control since they affect the main conducting structures surrounding the plasma column, providing passive stabilization but at the same time shielding the field generated by the active coils to control the plasma motion and shape. An extensive analysis was performed to assess the plasma vertical controllability and the modified requirements to the in-vessel vertical stability coils system as well as to the external Poloidal Field coils system. A similar analysis was aimed at assessing the performance of the shape control system in presence of the modified structures. The effect on plasma breakdown was also evaluated in terms of maximum initial loop voltage, quality of magnetic null and the flux loss related to the breakdown delay that was quantified under the same hypothesis employed by ITER for the baseline design. Furthermore, the modified design presents issues for the magnetic diagnostic system, related to the shielding of the probes by the eddy currents, which were analysed with a 3D model. The results of the analyses performed have some general interest in particular regarding the influence on plasma stability of 3D structures with close proximity to the plasma. The present paper aims at giving an overview of the analyses that have been carried out and a summary of the results in terms of impact of the modified design on plasma control and scenario, and in general an evaluation of the role of passive structure in plasma vertical stability and shape control. [ABSTRACT FROM AUTHOR]

• A new strategy for the sweeping control on DEMO device is developed. • The possibility to improve the sweeping control performance with in-vessel coils is investigated. • The compatibility of the sweeping control with vertical stability and shape control is investigated. • The sweeping performance has been validated by numerical simulations. In this paper, the sweeping control strategy is applied to DEMO single null configuration as possible solution for the power exhaust problem. Firstly, a possible sweeping control strategy is proposed to impose a periodic movement of the plasma divertor legs at a desired frequency with an almost fixed plasma shape. Then, the performance of the sweeping control using ex-vessel coils is analyzed in terms of current, voltage and maximum sweeping frequency. Finally, the possibility to implement the sweeping with the in-vessel coils is considered. Two possible solutions for the in-vessel coils have been adopted: a preliminary solution compatible with the actual DEMO port locations and an optimized solution that is more performing for the sweeping but needs to be validated for the compatibility with the remote handling. Numerical simulations demonstrate the effectiveness of the proposed approach coupling the sweeping control with the feedback control strategies for the plasma shape and position. [ABSTRACT FROM AUTHOR]

Abstract: In this study we derive linear models describing the dynamics of the n =0 plasma displacements around the main ITER equilibrium configurations. The models derived are consistent with the MHD equilibrium constraint as well as with the 3D geometry of the vacuum vessel and blanket outer triangular support where the main eddy currents flow takes place. Particular emphasis is placed on the analysis of the stability margin, growth time and minimum stabilization voltage. The performances of the present ITER control system (single loop) are compared to those of an upgraded system (double-loop) that is here proposed to improve the stability domain of the ITER plasmas forecast. [Copyright &y& Elsevier]

Abstract: A new model-based shape controller (XSC, i.e., eXtreme Shape Controller) able to operate with high elongation and triangularity plasmas has been designed and implemented at JET in 2003. The use of the XSC needs a number of steps, which at present are not automated and therefore imply the involvement of several experts. To help the session leader in preparing an experiment, a number of software tools are needed. The paper describes the SW tools that are currently in the developing phase, and describes the new framework for the preparation of a JET experiment. [Copyright &y& Elsevier]