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8 results on '"Doelman N."'

1. Controlled Mirror Motion System for Resonant Diplexers in ECRH Applications.

Author

Doelman, N., Van Den Braber, R., Kasparek, W., Erckmann, V., Bongers, W., Krijger, B., Stober, J., Fritz, E., Dekker, B., Klop, W., Hollmann, F., Michel, G., Noke, F., Purps, F., de Baar, M., Maraschek, M., Monaco, F., Müller, S., Schütz, H., and Wagner, D.

Subjects
*ELECTRON cyclotron resonance sources, *ELECTRIC waves, *RESONATORS, *MOTION, *CYCLOTRONS
Abstract

High-power resonant diplexers for millimetre waves have various promising applications in ECRH systems. The round-trip resonator length of a diplexer needs to be accurately tuned to match its prescribed functionality. For this purpose one of the mirrors in the FADIS MkIIa diplexer has been mounted on a motion system, in order to control the mirror to its desired location despite the presence of substantial disturbances. The mechanical properties and control strategy for the mirror motion system have been designed such as to meet the overall system requirements. The performance of the motion system has been experimentally validated in various high power mm-wave tests. [ABSTRACT FROM AUTHOR]

Published
2012
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2. Periodic brightening of Kepler light curves: investigating the possibility of forward scattering due to dust clouds.

Author

van Kooten, M A M, Kenworthy, M, and Doelman, N

Subjects
*BINARY stars, *SPACE telescopes, *STAR-branched polymers, *PHENOMENOLOGICAL theory (Physics), *ASTRONOMY, *LIGHT curves, *MINERAL dusts, *ECLIPSING binaries
Abstract

Dedicated transiting surveys, such as the Kepler space telescope, have provided the astronomy community with a rich data set resulting in many new discoveries. In this paper, we look at eight Kepler objects identified by Wheeler & Kipping with a periodic, broad increase in flux, that look distinctly different from intrinsic star variability. We consider two physical phenomena as explanations for these observed Kepler light curves; the first being the classical explanation while the second being an alternative scenario: (i) tidal interactions in a binary star system, and (ii) forward scattering from an optically thin cloud around an exoplanet. We investigate the likelihood of each model by modelling and fitting to the observed data. The binary system qualitatively does a good job of reproducing the shape of the observed light curves due to the tidal interaction of the two stars. We do, however, see a mismatch in flux right before or after the peak brightness. We find that six out of the eight systems require an F-type primary star with a K-type companion with large eccentricities. At the same time, we find that optically thin discs, modelled using a Henyey–Greenstein phase function are also able to generate these broad brightening events. Five of the eight observed objects can be described with this new hypothesis in the absence of RV observations. As the other three are not well-described by the disc model, we conclude that they are indeed heartbeat stars. [ABSTRACT FROM AUTHOR]

Published
2020
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3. Commissioning of inline ECE system within waveguide based ECRH transmission systems on ASDEX upgrade.

Author

Bongers, W. A., Kasparek, W., Doelman, N., Van den Braber, R., Van den Brand, H., Meo, F., de Baar, M. R., Amerongen, F. J., Donné, A. J. H., Elzendoorn, B. S. Q., Erckmann, V., Goede, A. P. H., Giannone, L., Grünwald, G., Hollman, F., Kaas, G., Krijger, B., Michel, G., Lubyako, L., and Monaco, F.

Subjects
*ELECTRON cyclotron resonance sources, *CYCLOTRONS, *WAVEGUIDES, *POLARIZATION (Nuclear physics), *POWER electronics
Abstract

A CW capable inline electron cyclotron emission (ECE) separation system for feedback control, featuring oversized corrugated waveguides, is commissioned on ASDEX upgrade (AUG). The system is based on a combination of a polarization independent, non-resonant, Mach-Zehnder diplexer equipped with dielectric plate beam splitters [2, 3] employed as corrugated oversized waveguide filter, and a resonant Fast Directional Switch, FADIS [4, 5, 6, 7] as ECE/ECCD separation system. This paper presents an overview of the system, the low power characterisation tests and first high power commissioning on AUG. [ABSTRACT FROM AUTHOR]

Published
2012
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4. Development of Resonant Diplexers for high-power ECRH -- Status, Applications, Plans.

Author

Kasparek, W., Plaum, B., Lechte, C., Wu, Z., Wang, H., Maraschek, M., Stober, J., Wagner, D., Reich, M., Schubert, M., Grünwald, G., Monaco, F., Müller, S., Schütz, H., Erckmann, V., Doelman, N., van den Braber, R., Klop, W., van den Brand, H., and Bongers, W.

Subjects
*ELECTRON cyclotron resonance heating, *ELECTRON cyclotron resonance sources, *ION beams, *WAVEGUIDES, *PLASMA gas research, *MATHEMATICAL models
Abstract

The development of diplexers for ECRH has been pursued at a number of institutes because of their attractive variety of applications: Power combination, non-mechanical, electrically controlled switching (of combined beams) between launchers with tens of kHz, and discrimination of low-power ECE signals from high-power ECRH is feasible. In a first part, this paper reports on plasma experiments with a ring resonator (Mk IIa) at ASDEX Upgrade. Commissioning experiments on fast switching between two launchers for synchronous stabilization of neoclassical tearing modes, as well as in-line ECE measurements have been performed, and experimental issues and first results are discussed. A clear influence of the switching phase on the amplitude of the 3/2 NTM mode was measured, complete stabilization could, however, not be demonstrated yet mainly due to imperfect resonator control. Concepts for improved tracking of the diplexers to the gyrotron frequency are presented. In a second part, the design of diplexers with ring resonators matched to HE11 fields is briefly discussed; these devices can be connected to corrugated waveguides without any mode converters. A compact version (MQ IV) is under investigation, which is compatible with the ITER ECRH system (170 GHz, 63.5 mm waveguide, vacuum tight casing), with the final goal of high-power tests at the 170 GHz gyrotron facility at JAEA in Naka, Japan. First low-power test results are presented. [ABSTRACT FROM AUTHOR]

Published
2015
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5. Status of Resonant Diplexer Development for high-power ECRH Applications.

Author

Kasparek, W., Plaum, B., Lechte, C., Filipovic, E., Erckmann, V., Grünwald, G., Hollmann, F., Maraschek, M., Michel, G., Monaco, F., Müller, S., Noke, F., Purps, F., Schubert, M., Schütz, H., Stober, J., Wagner, D., Van den Braber, R., Doelman, N., and Fritz, E.

Subjects
*RESONATORS, *ELECTRON cyclotron resonance sources, *CYCLOTRONS, *PLASMA gases, *POWER electronics
Abstract

Characteristics of ring resonator diplexers for high-power ECRH are briefly reviewed. Commissioning experiments performed on ASDEX Upgrade with the diplexer Mk IIa are presented, which demonstrate slow and fast switching of the power between two launchers, and thus the capability for efficient suppression of neoclassical tearing modes and simultaneous central heating of the plasma. The development of the compact diplexer Mk IIIb is discussed, and test results are presented. Finally, an evacuated design for 170 GHz is shown. [ABSTRACT FROM AUTHOR]

Published
2012
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6. Large Scale CW ECRH Systems: Meeting a Challenge.

Author

Erckmann, V., Kasparek, W., Plaum, B., Lechte, C., Petelin, M. I., Bruschi, A., D'Arcangelo, O., Bin, W., Braune, H., Van Den Braber, R., Doelman, N., Gantenbein, G., Laqua, H. P., Lubiako, L., Marushchenko, N. B., Michel, G., Thumm, M., and Stuttgart, IPF

Subjects
*ELECTRON cyclotron resonance sources, *ELECTRIC heating, *ELECTROMAGNETIC waves, *FUSION reactors, *PLASMA gases, *MAGNETOHYDRODYNAMICS, *GYROTRONS, *MAINTAINABILITY (Engineering), *RELIABILITY in engineering
Abstract

Electron Cyclotron Resonance Heating (ECRH) systems for next step-fusion devices like W7-X and ITER operate in CW-mode and provide a large flexibility to comply with various physics demands such as plasma start-up, heating and current drive, as well as configuration and MHD control. The request for many different sophisticated applications results in a growing complexity of the systems. This is in conflict with the request for high availability, reliability, and maintainability, which arises from DEMO demands. 'Advanced' ECRH-components must, therefore, comply with both the complex physics demands and operational robustness and reliability. The W7-X ECRH system is the first CW facility of an ITER relevant size and is used as a test bed for such components. Results on improvements of gyrotrons, transmission components and launchers are presented together with proposals for future developments. [ABSTRACT FROM AUTHOR]

Published
2011
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7. Robust sawtooth period control based on adaptive online optimization.

Author

Bolder, J. J., Witvoet, G., De Baar, M. R., Van De Wouw, N., Haring, M. A. M., Westerhof, E., Doelman, N. J., and Steinbuch, M.

Subjects
*SAWTOOTH generators, *PLASMA stability, *ADAPTIVE control systems, *COST functions, *TIME-varying systems, *FUSION reactors
Abstract

The systematic design of a robust adaptive control strategy for the sawtooth period using electron cyclotron current drive (ECCD) is presented. Recent developments in extremum seeking control (ESC) are employed to derive an optimized controller structure and offer practical tuning guidelines for its parameters. In this technique a cost function in terms of the desired sawtooth period is optimized online by changing the ECCD deposition location based on online estimations of the gradient of the cost function. The controller design does not require a detailed model of the sawtooth instability. Therefore, the proposed ESC is widely applicable to any sawtoothing plasma or plasma simulation and is inherently robust against uncertainties or plasma variations. Moreover, it can handle a broad class of disturbances. This is demonstrated by time-domain simulations, which show successful tracking of time-varying sawtooth period references throughout the whole operating space, even in the presence of variations in plasma parameters, disturbances and slow launcher mirror dynamics. Due to its simplicity and robustness the proposed ESC is a valuable sawtooth control candidate for any experimental tokamak plasma, and may even be applicable to other fusion-related control problems. [ABSTRACT FROM AUTHOR]

Published
2012
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8. Sawtooth period control strategies and designs for improved performance.

Author

Witvoet, G., Steinbuch, M., De Baar, M. R., Doelman, N. J., and Westerhof, E.

Subjects
*SAWTOOTH generators, *PLASMA confinement, *PLASMA stability, *HELIUM, *PERFORMANCE evaluation, *PUBLISHING
Abstract

The sawtooth instability is associated with the triggering of neo-classical tearing modes, core fuelling, α-confinement and the exhaust of thermal helium. Sawtooth control is therefore important for optimal reactor performance in ELMy H-modes. Control schemes for the sawtooth period have been published in the literature, but the systematic design of high-performance controllers (yielding accurate and fast convergent responses) has not been addressed. In this work, three control strategies for high-performance sawtooth control are presented using electron cyclotron current drive (ECCD). Both degrees of freedom of the ECCD actuator will be explored and combined with advanced controller designs. First, the ECCD deposition location is used as a control variable, for which a gain-scheduled feedback controller and static feedforward control is derived. Second, the use of the driven current as a control variable is explored, and a simple controller is designed based on the identified dynamics. In the third approach both control variables are joined in an overall controller design, which enables the combination of high-performance control of the sawtooth period and control of the gyrotron power. Time-domain simulations with a combined Kadomtsev-Porcelli sawtooth model show that each strategy obtains a better closed-loop performance than standard linear feedback techniques on merely the deposition location. [ABSTRACT FROM AUTHOR]

Published
2012
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