D. Mellein

Karlsruhe Institute of Technology, Carlsruhe, Baden-Württemberg, Germany

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Publications (5)2.3 Total impact

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    ABSTRACT: The ITER electron cyclotron upper port launching system has to provide local current drive in order to stabilize neoclassical tearing modes (NTMs) and the sawtooth instability. The mm-wave system is embedded in a rigid upper port plug structure optimized for the rough operating conditions. During regular operation the structure is heated by neutrons and photons which are simulated by the Monte-Carlo method. The structural system has to provide sufficient cooling especially in the front part where high heat loads occur. If the active plasma stabilization fails the worst case scenario for the upper port plugs is the upward vertical displacement event (VDE) followed by a fast current quench. The fast plasma disruption occurs close to the plugs; eddy currents are induced and interact with the strong static magnetic field. The resulting mechanical forces and torque moments stress the structural system to its physical limits; a detailed numerical analysis, prototype crosschecks and design optimization is required to obtain a working system for ITER. Numerical structural, thermal and fluid dynamic analyses are presented as well as prototype tests and finally the effect of plasma disruptions on the structural design is discussed.
    No preview · Article · Jun 2009 · Fusion Engineering and Design
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    ABSTRACT: Four ECH Upper Port Plugs are foreseen at ITER for counteracting plasma instabilities based on the injection of up to 20 MW mm-wave power at 170 GHz into the plasma. The required targeting of flux surfaces will be achieved by angular steering in the poloidal direction. The paper describes the main components of the mm-wave and structural system for the current reference design of the extended physics launcher (EPL). The mm-wave system is formed by waveguide and quasi-optical sections with a front steering system driven by a friction-less and backlash-free pneumatic system. The first tritium barrier is formed by a CVD diamond window with an indirect cooling concept that avoids direct water contact to the diamond disk and brazing material. The structure consists of the blanket shield module with the plasma facing first wall panel, the port plug frame, and the internal shield that provides adequate neutron shielding towards the launcher back-end. The key design requirements for the main structure are discussed with respect to efficient baking, to rigidity towards launcher deflection and to extraction of thermal loads. The current status of fabrication studies is presented demonstrating the feasibility of manufacturing routes for complex double wall structures. Testing of major port plug components is described in the context of dedicated test facilities and maintenance requirements.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7-X Stellarator (W7-X), which is under construction at IPP- Greifswald. A 10 MW ECRH plant with CW-capability at 140 GHz is under construction to meet the scientific objectives. The microwave power is generated by 10 gyrotrons with 1 MW each. Three gyrotrons are already operational at IPP in Greifswald. The W7-X gyrotrons are designed for single frequency operation at 140 GHz. The operation regime of the W7-X stellarator experiments is restricted to magnetic fields matched to the ECRH-frequency and it would be interesting to extend the operation regime to a second resonant magnetic field. Therefore gyrotron operation at a second frequency was investigated. The standard vertical collector sweep systems of gyrotrons inherently display a pronounced peaking of the collector heat loading. An improved collector sweep system was successfully tested on the TED gyrotrons, which creates an almost homogenous heat loading. This system is of particular interest for next generation gyrotrons with an output power up to 2 MW.
    No preview · Conference Paper · Oct 2007
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    ABSTRACT: Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7-X stellarator (W7-X) which is presently under construction at IPP Greifswald. The mission of W7-X is to demonstrate the inherent steady state capability of stellarators at reactor relevant plasma parameters. A modular 10 MW ECRH-plant at 140 GHz with 1 MW CW-capability power for each module is also under construction to support the scientific objectives. The commissioning of the ECRH-plant is well under way; three gyrotrons are operational. The strict modular design allows to operate each gyrotron separately and independent from all others. The ECRH-plant consists of many devices such as gyrotrons and high voltage power supplies, superconductive magnets, collector sweep coils, gyrotron cooling systems with many water circuits and last but not least the quasi-optical transmission line for microwaves with remote controlled mirrors and further water cooled circuits. All these devices are essential for a CW operation. A steady state ECRH has specific requirements on the stellarator machine itself, on the microwave sources, transmission elements and in particular on the central control system. The quasi steady state operation (up to 30 min) asks for real time microwave power adjustment during the different segments of one stellarator discharge. Therefore, the ECRH-plant must operate with a maximum reliability and availability. A capable central control system is an important condition to achieve this goal. The central control system for the 10 MW ECRH-plant at W7-X comprises three main parts. In detail these are the voltage and current regulation of each gyrotron, the interlock system to prevent the gyrotrons from damages and the remote control system based on a hierarchy set of PLCs and computers. The architecture of this central control system is presented.
    No preview · Article · Oct 2007 · Fusion Engineering and Design
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    ABSTRACT: Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7-X Stellarator (W7-X), which is under construction at IPP-Greifswald. A 10 MW ECRH plant with CW-capability at 140 GHz is under construction to meet the scientific objectives. The microwave power is generated by 10 gyrotrons with 1 MW each two gyrotrons are operational at IPP in Greifswald. The tubes are equipped with a single-stage depressed collector for energy recovery and operate with an output power modulation between 0.3 and 1 MW with a sinusoidal frequency of up to 10 kHz which is achieved by modulating the depression voltage and is an interesting feature for NTM control at ITER. The general features of the ECRH-plant such as frequency power, cw-capability, flexibility and the experimental experience are of high relevance for the ITER system. Each gyrotron is fed by two high-voltage sources. A high-power supply for driving the electron beam and a precision low-power supply for beam acceleration. The high-power facility consists of modular solid state HV-supplies (−65 kV 50/100 A) providing fast power control and high flexibility. The low-power high-voltage source for beam acceleration is realized by a feed back controlled high-voltage servo-amplifier driving the depression voltage. A protection system with a thyratron crowbar for fast power removal in case of gyrotron failure by arcing is installed. Both the high power and low-power high-voltage sources have the capability to supply a 2 MW ITER gyrotron without any modification. Analogue electronic devices control the fast functions of the high-voltage system for each gyrotron and a hierarchy of industrial standard PLCs and computers supervise the whole ECRH-plant.
    No preview · Article · Dec 2005 · Journal of Physics Conference Series