Showing papers by "R. C. Wolf published in 2014"

Study and design of the ion cyclotron resonance heating system for the stellarator Wendelstein 7-X

Abstract: The current status of the mechanical and electromagnetic design for the ICRF antenna system for W7-X is presented. Two antenna plugins are discussed: one consisting of a pair of straps with pre-matching to cover the first frequency band, 25–38 MHz, and a second one consisting of two short strap triplets to cover a frequency band around 76 MHz. This paper focusses on the two strap antenna for the lower frequency band. Power coupling of the antenna to a reference plasma profile is studied with the help of the codes TOPICA and Microwave Studio that deliver the scattering matrix needed for the optimization of the geometric parameters of the straps and antenna box. Radiation power spectra for different phasings of the two straps are obtained using the code ANTITER II and different heating scenario are discussed. The potential for heating, fast particle generation, and current drive is discussed. The problem of RF coupling through the plasma edge and of edge power deposition is summarized. Important elements of the complete ion cyclotron resonance heating system are discussed: a resonator circuit with tap feed to limit the maximum voltage in the system, and a decoupler to counterbalance the large mutual coupling between the 2 straps. The mechanical design highlights the challenges encountered with this antenna: adaptation to a large variety of plasma configurations, the limited space within the port to accommodate the necessary matching components and the watercooling needed for long pulse operation.

Limiter for the early operation phase of W7-X

Abstract: Wendelstein 7-X [1] is an optimized modular stellarator to come into operation in 2015. In the first operational phase of W7-X a dedicated limiter configuration will be exploited to study ECRH heating scenarios, confinement properties and edge physics [2]. In this contribution the dedicated magnetic configuration is presented and the limiter design for this early phase is explained. The position of the main stellarator islands in this configuration is shifted radially outwards in order to have closed flux surfaces in front and in the shadow of the limiter for at least several centimeters. In such a way the first wall behind the limiter, mainly copper, can be expected to receive a negligible power fraction. Five inboard limiters in the symmetry planes of the machine are planned. The limiter shape is chosen in such a way as to distribute the heat flux as evenly as possible. Field line tracing with field line diffusion and construction of magnetic coordinates are used [3]. Field line diffusion simulates energy convection parallel to the field lines and the perpendicular diffusion and is determined by the choice of the field line diffusion coefficient D f l = D⊥/υ‖. Magnetic coordinates, e.g. Boozer coordinates, describe a flux surface as a double Fourier series, where the coefficients are found numerically from field line tracing. Given such a Fourier representation of the last closed flux surface and an assumed radial heat decay length, as follows from diffusion coefficient and magnetic configuration, the limiter shape can be formed to have a desired heat flux distribution. The 3D shape of the limiter chosen for the W7-X early operation phase is presented here. Further, a tolerance study of the main parameters defining the limiter performance is presented. This includes a variation of the diffusion coefficient, limiter positioning tolerances and field errors. Preliminary result of the limiter simulation with EMC3-EIRENE will be given in [4]. From the experimental point of view, the limiter operation is an opportunity to measure perpendicular diffusion, especially because the limiter combines distinct zones with significantly different connection lengths.

Review of the safety concept for fusion reactor concepts and transferability of the nuclear fission regulation to potential fusion power plants

Abstract: 1Gesellschaft für Anlagenund Reaktorsicherheit (GRS) mbH, Boltzmannstraße 14, 85748 Garching, Germany, Joachim.Herb@grs.de 2Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany 3Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Wendelsteinstraße 1, 17491 Greifswald, Germany 4Karlsruhe Institute of Technology (KIT), Institute for Neutron Physics and Reactor Technology, Herrmann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany 5Öko-Institut e.V. (Institute for Applied Ecology), Rheinstraße 95, 64295 Darmstadt, Germany LoD Operational state Objective Means Consequences dose limit 1 Normal operation Prevention of abnormal operation and failures Conservative design high quality in construction, operation No measure

Forward Modeling of a High Resolution X-ray Imaging Crystal Spectrometer for the Wendelstein 7-X Stellarator

Abstract: Introduction For the measurement of radial ion temperature Ti and poloidal flow velocity profiles vФ at the Wendelstein 7-X (W7-X) stellarator, the installation of two high resolution X-ray imaging spectrometer systems of the Johann-type is under preparation [1-3]. Wavelength selection by Bragg-reflection (λ = 4 A) is achieved with a spherically bent crystal [3], providing a radial profile of the Heor H-like spectrum of selected (mainly Argon due to a broad radial range of existence in the bulk plasma) impurities. This paper presents a full forward modeling of the spatial and energy resolved intensity pattern on a 2D CCD detector of the High Resolution X-ray Imaging Spectrometer system HR-XIS [1] using the Minerva Bayesian analysis framework [4]. This framework provides an elegant way of calculating radial profiles of plasma parameters from line-integrated measurements.