1,721,225 research outputs found
PLASMA MAGNETIC AND KINETIC CONTROL IN A TOKAMAK
No full textThe search of new resources has become crucial in this time of increasing energy demand. Research in nuclear fusion field tries to give an answer to this request. Its main aim is to bring the Sun on Earth", that is to find a viable way to produce energy by the same fusion reaction that occurs in the stars. If one day this goal is achieved a clean, safe and theoretically inexhaustible source of energy will be made available to all mankind. The role of automatic control in today experimental thermonuclear fusion devices is becoming more and more significant. New control systems should be designed to achieve the requirements for an economically attractive steady-state fusion power plant. The control systems which interact with the fully ionized gas (plasma)in the reactor vacuum chamber can be classified into two main categories: - magnetic control systems - kinetic control systems The magnetic control systems deal with macroscopic properties of the plasma such as its vertical velocity, its shape and the current flowing through it. All these features can be related to the magnetic field generated by several surrounding coils. The kinetic control systems, instead, control the transport characteristics of the plasma, that is the internal profiles of current density, temperature and density. To achieve this goal the kinetic control systems make use of the heating and fuelling actuators. Thanks to the availability of reliable models, the magnetic control problem has been successfully solved and different approaches have been proposed to control the plasma position, shape and current in all the existing thermonuclear fusion facilities. As far as the control of the internal kinetic profiles is concerned, only preliminary results have been achieved so far, and only some first attempts of feedback control have been performed. The main problems preventing a good performances achievement with a kinetic control system are: - the lack of simple models able to catch the main transport phenomena which occur during a plasma discharge - the reliability of the available measurements, which is not always satisfactory, especially for those near the plasma center. For these reasons further improvements in modelling and diagnostics are crucial and should be made before a controller with acceptable performances could be designed. In this thesis we deal with both the magnetic and kinetic control problems. In particular the thesis has been divided into two parts: Part I is mainly related with the design, the implementation and the experimental results of the new shape controller (eXtreme Shape Controller, XSC) that has been deployed at the Joint European Torus tokamak. Part II deals with the identification of a dynamic model suitable for the design of a plasma kinetic profiles controller. Special attention is given in Part I to the implementation details, since the author of this thesis has temporarily joined the JET plasma position and current control team during the shape controller development. It is worth to notice that, apart from the review of plasma transport physics, only preliminary results are given in Part II as far as the modelling is concerned. In fact the modelling aimed to the design of a controller for the plasma internal profiles is among the subjects that are still under investigation by both the plasma physics and control communities
Fusion, tokamaks, and plasma control - An introduction and tutorial
No full textThe paper discusses the process behind fusion reaction, the magnetic confinement of plasma to sustain fusion reactions, different kinds of tokamaks used for the magnetic plasma confinement, the operation of tokamaks, and the control of tokamaks. Control of tokamaks concerns the basic functions of plasma initiation, shaping, heating, current drive, stabilization, and safe termination of charges
Reduced order solutions for the singular H∞ filtering problem
No full textIn this paper we consider the finite horizon filtering H∞ problem for linear time varying systems. This problem has already been solved in the case when the direct feedthrough matrix F between the disturbance and the output vectors is full row rank. Here we consider the case when the problem is singular, i.e. the matrix F is not full row rank. We will show that in this case a reduced observer can be designed in order to meet the desired performance
Plasma shape control for the JET Tokamak - An optimal output regulation approach
No full textThe eXtreme Shape Controller, designed and implemented on the JET tokamak, was described. The controller regulates the plasma shape as specified in terms of plasma-wall distances and maintains this plasma shape in the presence of significant variations of critical plasma parameters, namely the poloidal beta, the internal inductance, and the plasma current. The design procedure is based on the SVD of the plant output matrix. This procedure accounts for specifications on the accuracy of the controller variables as well as the maximum allowable control effort. The new controller has been fully commissioned on the JET tokamak, is in regular operation, and is delivering the expected performance
Safe abstractions of data encodings in formal security protocol models
Full text linkWhen using formal methods, security protocols are usually modeled at a high level of abstraction. In particular, data encoding and decoding transformations are often abstracted away. However, if no assumptions at all are made on the behavior of such transformations, they could trivially lead to security faults, for example leaking secrets or breaking freshness by collapsing nonces into constants. In order to address this issue, this paper formally states sufficient conditions, checkable on sequential code, such that if an abstract protocol model is secure under a Dolev-Yao adversary, then a refined model, which takes into account a wide class of possible implementations of the encoding/decoding operations, is implied to be secure too under the same adversary model. The paper also indicates possible exploitations of this result in the context of methods based on formal model extraction from implementation code and of methods based on automated code generation from formally verified model
Provably correct Java implementations of Spi Calculus security protocols specifications
Full text linkSpi Calculus is an untyped high level modeling language for security protocols, used for formal protocols specification and verification. In this paper, a type system for the Spi Calculus and a translation function are formally defined, in order to formalize the refinement of a Spi Calculus specification into a Java implementation. The Java implementation generated by the translation function uses a custom Java library. Formal conditions on such library are stated, so that, if the library implementation code satisfies such conditions, then the generated Java implementation correctly simulates the Spi Calculus specification. A verified implementation of part of the custom library is further presente
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