The huge energy stored in the Large Hadron Collider (LHC) could potentially cause severe damage when the superconducting state disappears (quench) if precautions are not taken. Most of the superconducting elements in this accelerator require protection in case of resistive transition. The reliability of the Quench Protection System will have a very important impact on the overall LHC performance.Existing high energy accelerators were conceived as prototypes whose main objective was not the efficiency but to push the performance to the limit. The LHC will be the first large accelerator with reliability oriented design.This thesis focuses on adapting the reliability theory and methods that are currently used by the industry and small accelerators to the protection systems of larger and more complex machines like the LHC. Two main contributions have been achieved. Firstly, the author has developed an analytical model for a general multi-state protection system, which is able to include the specific characteristics of a large superconducting accelerator. In order to provide a tool for its implementation and related computations, the simulation program RESQP (REliability Software for Quench Protection studies) has been developed. Secondly, a theoretical and experimental analysis of the LHC Quench Protection System dependability has been carried out.

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ITER is a long-pulse tokamak with elongated plasma. The nominal inductive operation produces a D-T fusion power of 500 MW for a burn length of 300-500 s, with the injection of 50 MW of auxiliary power. With non-inductive current drive from the H&CD systems, the burn duration is envisaged to be extended to 3000 s.The term ITER Instrumentation & Control (I&C) includes everything required to operate the ITER facility. It comprises three vertical tiers; conventional control, interlock system and safety system, and two horizontal layers; central I&C systems and plant system I&C. CODAC (Control, Data Access and Communication) system forms the upper level of the hierarchy, and is the conventional central control system of ITER architecture. CODAC system is responsible for integrating all plant system I&C and enable operation of ITER as a single integrated plant. CODAC system provides overall plant systems coordination, supervision, plant status monitoring, alarm handling, data archiving, plant visualization (HMI) and remote experiment functions. CIS (Central Interlock System) and CSS (Central Safety System) also form the upper level of the hierarchy to supervising and integrating all plant system interlock and safety functions. Plant system I&C forms the lower level of the hierarchy, and provide dedicated plant data acquisition, plant status monitoring, plant control and plant protection functions to perform individual plant system operation under the supervision of central I&C systems.

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