A. Collazos

École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland

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Publications (25)3.6 Total impact

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    ABSTRACT: The Electron Cyclotron (EC) system for the ITER tokamak is designed to inject ≥20 MW RF power into the plasma for Heating and Current Drive (H&CD) applications. The EC system consists of up to 26 gyrotrons (between 1 and 2 MW each), the associated power supplies, 24 transmission lines and 5 launchers. The EC system has a diverse range of applications including central heating and current drive, current profile tailoring and control of plasma magneto-hydrodynamic (MHD) instabilities such as the sawtooth and neoclassical tearing modes (NTMs). This diverse range of applications requires the launchers to be capable of depositing the EC power across nearly the entire plasma cross section. This is achieved by two types of antennas: an equatorial port launcher (capable of injecting up to 20 MW from the plasma axis to mid-radius) and four upper port launchers providing access from inside of mid radius to near the plasma edge. The equatorial launcher design is optimized for central heating, current drive and profile tailoring, while the upper launcher should provide a very focused and peaked current density profile to control the plasma instabilities.The overall EC system has been modified during the past 3 years taking into account the issues identified in the ITER design review from 2007 and 2008 as well as integrating new technologies. This paper will review the principal objectives of the EC system, modifications made during the past 2 years and how the design is compliant with the principal objectives.
    Fusion Engineering and Design. 01/2011;
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    ABSTRACT: The ITER Heating and Current Drive Upper Launcher (H & CD EC UL) uses a pneumomechanical steering-mirror assembly (SMA) to steer the RF beams for their deposition in the appropriate location in the plasma to control magnetohydrodynamic activity (neoclassical tearing modes (NTMs) and sawtooth oscillations). For NTM stabilization, the mirror rotation needs to be controlled to an accuracy that is better than 0.1??. A 10????s<sup>-1</sup> mirror steering speed is also required. To assess the performance of the two SMA prototypes that have been manufactured, a test stand that reproduces the expected pneumatic configuration of the UL has been built. So far, only the first SMA prototype has been tested, and tests on the second prototype are foreseen in the 2009-2010 period. The steering angle of the mirror will be deduced from the pressure applied to the mechanism since there is no in situ angle measurement at present. An ??off-the-shelf?? commercial servo valve with a proportional-integral-derivative controller has been used to control the pressure with good results for the switching cycle. These tests show that a more advanced controller will be required to attain the desired accuracy and speed for the modulation cycles.
    IEEE Transactions on Plasma Science 04/2010; · 0.87 Impact Factor
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    ABSTRACT: A full quasi‐optical setup for the internal optics of the Front Steering Electron Cyclotron Resonance Heating (ECRH) Upper Launcher for ITER was designed, proving to be feasible and favorable in terms of additional flexibility and cost reduction with respect to the former design [1]. This full quasi‐optical solution foresees the replacement of the mitre‐bends in the final section of the launcher with dedicated free‐space mirrors to realize the last changes of directions in the launcher. A description of the launcher is given and its advantages presented. The parameters of the expected output beams as well as preliminary evaluations of truncation effects with the physical optics GRASP code are shown. Moreover, a study of mitre‐bends replacement with single mirrors for multiple beams is described. In principle it could allow the beams to be larger at the mirror locations (with a further decrease of the peak power density due to partial overlapping) and has the additional advantage to get a larger opening with compressed beams to avoid conflicts with side‐walls port. Constraints on the setup, arising both from the resulting beam characteristics in the space of free parameters and from mechanical requirements are taken into account in the analysis.
    AIP Conference Proceedings. 11/2009; 1187(1):547-550.
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    ABSTRACT: This paper reviews the design and functionality of the 24 MW 170 GHz electron cyclotron heating and current drive system being planned for the ITER Tokamak. The sub-systems (power supplies, gyrotrons, transmission lines and launcher antennas) are described based on present day technologies, while on-going R&D provides component and sub-system testing with the possibility of increasing the reliability of the overall EC system. Modifications to the steering ranges of the launching antennas are under investigation that can improve the functional capabilities of the EC system without increasing cost and relaxing the engineering constraints.
    Infrared, Millimeter, and Terahertz Waves, 2009. IRMMW-THz 2009. 34th International Conference on; 10/2009
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    ABSTRACT: Four of the 16 ITER upper port plugs will be devoted to electron cyclotron resonance heating (ECRH) in order to control the magneto-hydrodynamic (MHD) instabilities.In order to achieve the stabilisation of the neoclassical tearing modes (NTM) and sawtooth oscillation, a deposition of a very localized, narrow and peaked current density profile over a broad poloidal steering range at the ITER rational surfaces q=1 to q=3/2 and q=2 is required [1]. The quasi-optical configuration consists of eight mm-wave beams entering each of the four upper launchers (UL) through waveguides into the vacuum vessel. Each beam is then directed to the plasma using a serial arrangement of four mirrors, the first set of 2 (mirrors M1 and M2) zigzag the beam line to avoid stray radiation, while the beam-waist locations and beam-shaping properties in the vacuum vessel are defined by the last two mirrors, a static focusing mirror (M3) and a flat poloidally-steerable mirror (M4). These last mirrors (M3 and M4) reflect a group of four beams coming of four individual M1/M2. The plane mirror M4 is steered using a backlash and friction free mechanism that is pneumatically actuated using helium gas. A first prototype of this has been manufactured as a proof of principle and tested for controller design purposes. A second prototype, ITER compatible in terms of the materials used and cooling circuits, will be subject to similar tests throughout the last half of 2009 period.The UL mirrors (static and steerable) absorb heat generated essentially by three sources: the ohmic loss of the RF beam reflected at the mirror surfaces (which is mirror-temperature dependant) and by nuclear (volumetric heating) and thermal radiation (surface heating) coming from the plasma. While the average heat load is calculated to be 2MW beam compatible with reasonable engineering limits, three more important constraints conditioned the actual mirror design, the peak ohmic heat load (the electromagnetic forces generated in ver- tical disruption events (VDE), and the ITER cooling water requirements. This paper provides an overview of the different upper port-plug mirror designs and stresses several different prototype manufacturing methods for the steering mirror, outlining lessons learned.
    Fusion Engineering, 2009. SOFE 2009. 23rd IEEE/NPSS Symposium on; 07/2009
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    ABSTRACT: The purpose of the ITER electron cyclotron resonance heating (ECRH) upper launcher (UL), or antennae will be to provide localised current drive by accurately directing mm-wave beams up to 2MW, out of the four allocated upper port plugs, at chosen rational magnetic flux surfaces in order to stabilise neoclassical tearing modes (NTMs). This paper will present an overview of the UL, with emphasis on the mm-wave components. The mm-wave layout includes corrugated waveguide sections and a quasi-optical path with both focusing mirrors and plane steering mirrors. One of the essential components of the UL is the Steering Mechanism Assembly (SMA), providing variable poloidal injection angles fulfilling high deposition accuracy requirements at the plasma location. The Actuator principle and rotor bearings are frictionless and backlash free, avoiding tribological difficulties such as stickslip and seizure. The underlying working principle is the use of mechanically compliant structures. Validation and proof testing of the steering principle is achieved with an uncooled first prototype demonstrator. A second prototype is currently being manufactured, comprising the functionalities needed for the ITER compatible system such as water cooling and high power mm-wave compatibility. In order to perform the fatigue tests of the actuator bellows, a test facility has been built, under ITER-like vacuum and temperature working conditions. Results of the cyclic fatigue tests are compared to the various manufacturer standards and codes, combining stress and strain controlled material fatigue properties.
    Fusion Engineering and Design. 06/2009;
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    ABSTRACT: The challenge of developing the conceptual design of the ECH Upper Launcher system for MHD control in the ITER plasmas has been tackled by team of European Associations together with the European Domestic Agency (“F4E”). The launcher system has to meet the following requirements: (a) a mm-wave system extending from the interface to the transmission line up to the target absorption zone in the plasma and performing as an intelligent antenna; (b) a structural system integrating the mm-wave system and ensuring sufficient thermal and nuclear shielding; (c) port plug remote handling and testing capability ensuring high port plug system availability. The paper describes the reference launcher design. The mm-wave system is composed of waveguide and quasi-optical sections with a front steering system. An automated feedback control system is developed as a concept based on an assimilation procedure between predicted and diagnosed absorption location. The structural system consists of the blanket shield module, the port plug frame, and the internal shield for appropriate neutron shielding towards the launcher back-end. The specific advantages of a double walled structure are discussed with respect to adequate baking, to rigidity towards launcher deflection under plasma-generated loads and to removal of thermal loads, including nuclear ones. Basic studies of remote handling (RH) to validate design development are initiated using a virtual reality simulation backed by experimental validation, for which a launcher handling test facility (LHT) is set up as a full scale experimental site allowing furthermore thermohydraulic studies with ITER blanket water parameters.
    Fusion Engineering and Design. 06/2009;
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    ABSTRACT: The aim of the ITER electron cyclotron heating and current drive upper launcher (UL) is to control magnetohydrodynamic activity in the plasma, in particular neoclassical tearing modes, requiring a narrow and peaked deposition of the radio-frequency (rf) power. The millimeter-wave (mm-wave) system of the UL is optimized to ensure that the eight rf beams are all focused to a small beam width at the resonance location. The present design uses two mitre bends per beam and a focusing mirror for each set of four beams, orientating each set onto a single steering mirror (SM) to inject it into the plasma. The SM is rotated using a frictionless and backlash free pneumo-mechanical system. A first prototype of the SM has been constructed to demonstrate the manufacturability and the actuation principle and to develop an adequate control strategy. A test program has been developed to ensure the integrity of the launcher from the pre-build-to-print design phase (research and development) up to the tests after maintenance. This paper presents a general overview of the system, a description of the progress in the mm-wave optical layout, low-power tests, alignment specifications of the mm-wave components, and SM capabilities to meet the ITER requirements.
    04/2009;
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    ABSTRACT: The main objective of the ITER ECRH upper launcher (UL) is to control magnetohydrodynamic activity, in particular neoclassical tearing modes (NTMs), by driving several MW of EC current near the q = 1, 3/2, 2 flux surfaces, where NTMs are expected to occur.The steering of the EC power is done by the steering mechanism assembly (SMA) that comprises a reflecting mirror and a frictionless and backlash free pneumo-mechanical system actuated with pressurised helium gas. The control requirements for this component in terms of steering accuracy and speed are reviewed. With respect to these requirements, the performance of the first SMA prototype is assessed in a mock up of the UL pneumatic configuration.The expected design characteristics of the SMA have been verified and an overall satisfactory performance has been assessed. Furthermore, the main challenges for the future work, such as the pressure and angular position control, have been identified.
    Fusion Engineering and Design. 01/2009;
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    ABSTRACT: A predictive optimal control system for micro-cogeneration in domestic applications has been developed. This system aims at integrating stochastic inhabitant behavior and meteorological conditions as well as modelling imprecisions, while defining operation strategies that maximize the efficiency of the system taking into account the performances, the storage capacities and the electricity market opportunities. Numerical data of an average single family house has been taken as case study. The predictive optimal controller uses mixed-integer and linear programming where energy conversion and energy services models are defined as a set of linear constraints. Integer variables model the start-up and shut-down operations as well as the load dependent efficiency of the cogeneration unit. The proposed control system has been validated using more complex building and technology models to asses model inaccuracies. Typical demand profiles for stochastic factors have been used. The system is evaluated in the perspective of its usage in Virtual Power Plants applications.
    01/2009;
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    ABSTRACT: Four of the 16 ITER upper port plugs will be devoted to electron cyclotron resonance heating (ECRH) in order to control magnetohydrodynamic (MHD) instabilities [1] and [2]. In order to achieve the stabilisation of the neoclassical tearing modes (NTM) and sawtooth oscillation, a deposition of a very localized and peaked current density profile over a broad poloidal steering range is required.In the present optical configuration eight 2 MW mm-wave beams enter each of the four upper launchers (UL) through waveguides into the vacuum vessel. Each beam line comprises consecutive corrugated waveguide sections with two mitre bends, orientating the poloidal and toroidal directions and three sections of quasi-optical transmission [3].The beam waist locations and beam shaping properties in free space propagation are defined by two additional mirrors, the first being a static focusing mirror and the second a plane poloidally steerable mirror. Each mirror reflects a group of 4 mm-wave beams.The three types of UL mirrors (mitre bend, focusing and steering) absorb heat generated essentially by three sources: the ohmic loss of the RF beam reflected at the mirror surfaces and the nuclear and thermal radiation coming from the plasma. While the average heat load is within reasonable engineering limits, three elements condition the actual mirror design, the peak ohmic heat load (Gaussian or Bessel type heat deposition profiles), the electromagnetic forces generated in vertical disruption events (VDE), and the ITER cooling water requirements.This paper provides an overview of the different upper port-plug mirror designs and cooling schemes and an outlook on the prototype manufacturing activities and the future test program. The optimized mm-wave layout within the ECH port plugs is also presented.
    Fusion Engineering and Design. 01/2009;
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    ABSTRACT: The ITER electron cyclotron (EC) upper port antenna (or launcher) is nearing completion of the detailed design stage and the final build-to-print design stage will soon start. The main objective of this launcher is to drive current locally to stabilize the neoclassical tearing modes (NTMs) (depositing ECCD inside of the island that forms on either the q = 3/2 or 2 rational magnetic flux surfaces) and control the sawtooth instability (deposit ECCD near the q = 1 surface). The launcher should be capable of steering the focused beam deposition location to the resonant flux surface over the range in which the q = 1, 3/2 and 2 surfaces are expected to be found for various plasma equilibria susceptible to the onset of NTMs and sawteeth. The aim of this paper is to provide the design status of the principal components that make up the launcher: port plug, mm-wave system and shield block components. The port plug represents the chamber that provides a rigid support structure that houses the mm-wave and shield blocks. The mm-wave system comprises the components used to guide the RF beams through the port plug structure and refocus the beams far into the plasma. The shield block components are used to attenuate the nuclear radiation from the burning plasma, protecting the fragile in-port components and reducing the neutron streaming through the port assembly. The design of these three subsystems is described; in addition, the relevant thermo-mechanical and electro-magnetic analyses are reviewed for critical design issues.
    Nuclear Fusion 04/2008; 48(5):054013. · 2.73 Impact Factor
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    ABSTRACT: The ITER ECH upper launcher is devoted to directing up to eight 2-MW beams per port plug over half of the plasma cross section. A focusing mirror is used to achieve a very narrow deposition profile to stabilize MHD activity such as the neoclassical tearing modes (NTMs) and the sawtooth oscillation. The beam deposition location is changed via a steering mirror with up to plusmn7 deg (plusmn14 deg beam), which allows access from inside mid radius out to nearly the plasma edge. The steering mechanism uses a frictionless backlash free system to avoid sticking, thus increasing the reliability. A small percentage (<0.5%) of the beam is absorbed upon each reflection from the mirror surface, resulting in absorbed peak power densities ranging from ~2.0 MW/m<sup>2</sup> (focusing and steering mirrors) to 3.6 MW/m<sup>2</sup> (waveguide mitre bend mirror). The cooling of each mirror has been analysed under ITER conditions using theoretical and finite element modeling (using ANSYS and ANSYSWORKBENCH). The design optimization of the steering mirror has been given considerable attention, aiming at lowering the peak heat load density, while limiting the induced current from the incident changing magnetic field that occurs during a plasma disruption event. The analysis of the mitre bend mirror has been compared to experimental data taken from long pulse (up to 1000 s) , high power (0.3 to 0.8 MW) operation, which has been performed in collaboration with with JAEA, GA, CNR EFDA and CRPP to validate the FE results and to demonstrate that it can withstand high power densities arising from up to 2 MW incident power. This paper will overview the current design status along with the critical design issues for the different in-launcher mirrors.
    Fusion Engineering, 2007. SOFE 2007. 2007 IEEE 22nd Symposium on; 07/2007
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    ABSTRACT: The ITER ECRH upper port antenna (or launcher) will be used to drive current locally for stabilising the neoclassical tearing mode (NTM) by depositing ram-wave power inside of the island which forms on the q=3/2 or 2 rational magnetic flux surfaces and control the sawtooth instability by driving current near the q=l surface. This requires the launcher to be capable of steering the focused beam deposition location across the resonant flux surface over the range where the q=l, 3/2 and 2 surfaces are expected to be found (roughly the outer half of the plasma). ITER'S present reference design uses a front steering (FS) concept, which uses a moveable mirror close to the plasma. Two separate mirrors are used to decouple the focusing and steering aspects resulting in an optimized optical configuration providing a well focused beam over a large steering range. The steering mechanism providing the mirror rotation uses a frictionless and backlash free mechanical system based on the elastically compliant deformation of structural components to avoid the in vessel tribological difficulties. Traditional designs are based on push-pull rods acting on a mirror which rotates with ball bearings, they present the risk of gripping or result in stick-slip movements. The ball bearings are replaced with a set of flexure pivots while the classic actuation through a push-pull rod scheme is replaced by a directly acting pneumatic system consisting on a fast feed line, bellows and springs, in which the pressure acting on the bellows pushes the mirror against the compressive springs. The rotation of the mirror is thus produced by the counteraction between the forces exerced by the springs and the bellows, themselves piloted by the pressure of the system. A servovalve placed outside of the port plug and connected to the bellows by a small tube will control this pressure. The system also includes flexible water cooling pipes which allow the removal of heat generated by the ohmic surface losses - of the reflected mm-wave beams and the nuclear and radiation volumic heating of the rotating mirror components. This paper will give an overview of the engineering and design issues and their solutions, and provide the development status of the different components of the mechanism. Special attention will be given to the engineering analysis performed to ensure compliance of the steering mechanism with the various ITER requirements.
    Fusion Engineering, 2007. SOFE 2007. 2007 IEEE 22nd Symposium on; 07/2007
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    ABSTRACT: The main objective of the ITER ECRH Upper Launcher (UL) is to control magnetohydrodynamic (MHD) activity: sawtooth oscillations and neoclassical tearing modes. 170GHz RF beams are oriented and focused to obtain a maximum overlapping of the waists of all the beams throughout the deposition location range in the plasma. The steering of the beams is done using 8 independent steering mirrors (SM) placed in the front par t of each one of the four dedicated por t plugs. Accurate and rapid control of the SMs for directing the beams at the required location is crucial in order to achieve an efficient MHD control. An assessment of the SM first prototype capabilities to meet the ITER requirements has been carried out giving promising results for this application.
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