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Garching, Germany

The Max-Planck-Institut für Plasmaphysik is a physics institute for the investigation of plasma physics, with the aim of working towards fusion power. The institute also works on surface physics, also with focus on problems of fusion power.The IPP is an institute of the Max-Planck-Gesellschaft, part of the European Fusion Program , and an associated member of the Helmholtz Association.The IPP has two sites: Garching near Munich and Greifswald , both in Germany.It owns several large devices, namely the experimental tokamak ASDEX Upgrade the experimental stellarator Wendelstein 7-AS the experimental stellarator Wendelstein 7-X a tandem acceleratorIt also cooperates with the ITER and JET projects. Wikipedia.

Von Toussaint U.,Max Planck Institute for Plasma Physics (Garching)
Reviews of Modern Physics

Bayesian inference provides a consistent method for the extraction of information from physics experiments even in ill-conditioned circumstances. The approach provides a unified rationale for data analysis, which both justifies many of the commonly used analysis procedures and reveals some of the implicit underlying assumptions. This review summarizes the general ideas of the Bayesian probability theory with emphasis on the application to the evaluation of experimental data. As case studies for Bayesian parameter estimation techniques examples ranging from extra-solar planet detection to the deconvolution of the apparatus functions for improving the energy resolution and change point estimation in time series are discussed. Special attention is paid to the numerical techniques suited for Bayesian analysis, with a focus on recent developments of Markov chain Monte Carlo algorithms for high-dimensional integration problems. Bayesian model comparison, the quantitative ranking of models for the explanation of a given data set, is illustrated with examples collected from cosmology, mass spectroscopy, and surface physics, covering problems such as background subtraction and automated outlier detection. Additionally the Bayesian inference techniques for the design and optimization of future experiments are introduced. Experiments, instead of being merely passive recording devices, can now be designed to adapt to measured data and to change the measurement strategy on the fly to maximize the information of an experiment. The applied key concepts and necessary numerical tools which provide the means of designing such inference chains and the crucial aspects of data fusion are summarized and some of the expected implications are highlighted. © 2011 American Physical Society. Source

Maraschek M.,Max Planck Institute for Plasma Physics (Garching)
Nuclear Fusion

Neoclassically driven tearing modes (NTMs) are a major problem for tokamaks operating in a conventional ELMy H-mode scenario. Depending on the mode numbers these pressure-driven perturbations cause a mild reduction in the maximum achievable βN=βt/(Ip/aBt) before the onset of the NTM, or can even lead to disruptions at a low edge safety factor, q95. A control of these types of modes in high βN plasmas is therefore of vital interest for magnetically confined fusion plasmas. The control consists of two major approaches, namely the control of the excitation of these modes and the removal, or at least mitigation, of these modes, once an excitation could not be avoided. For both routes examples will be given and the applicability of these approaches to ITER will be discussed. © 2012 IAEA, Vienna. Source

The derivation of electromagnetic gyrofluid equations is made systematic by using the Hermite polynomial form of the underlying delta- f gyrokinetic distribution function. The gyrokinetic free-energy functional is explicitly used to set up the model. The gyrofluid free energy follows directly. The interaction term in the gyrokinetic Lagrangian is used to obtain the gyrofluid counterpart, from which the polarization equation follows. One closure rule is decided for taking moments over the kinetic gyroaveraging operator. These steps fix the rest of the derivation of the conservative part of the gyrofluid equations. Dissipation is then added in a form to obtain positive definite dissipation and to obtain the collisional fluid equations in their appropriate limit. Existing results are recovered, with the addition of a completely consistent model for finite gyroradius effects in the nonlinearities responsible for magnetic reconnection. © 2010 American Institute of Physics. Source

Zohm H.,Max Planck Institute for Plasma Physics (Garching)
Fusion Science and Technology

A set of simple scaling relations is derived to assess the impact of plasma physics and technology assumptions on the design of a DEMO tokamak fusion reactor. At the same time, it is shown that by postulating that the plasma physics assumptions are consistent with those that can be reliably reached in present-day experiments and that the recirculating power is reasonably low, a tokamak DEMO operating with steady-state plasma operation is of large size, comparable to a reactor-suggesting that the study of pulsed options should receive more attention in the future. The scaling relations reproduce well the results from a number of previous studies, indicating that they are particularly well suited for future parametric scoping studies. From the relations derived, it also follows that the areas in which future progress will have a particularly large impact on the attractiveness of DEMO are the ß limit in plasma physics and in technology the magnetic field strength B1 and the wall-plug efficiency ηCD of the systems to drive noninductive current. Source

Zohm H.,Max Planck Institute for Plasma Physics (Garching)
Nuclear Fusion

Recent experiments on the ASDEX Upgrade tokamak aim at improving the physics base for ITER andDEMOto aid the machine design and prepare efficient operation. Type I edge localized mode (ELM) mitigation using resonant magnetic perturbations (RMPs) has been shown at low pedestal collisionality (v.ped 0.4). In contrast to the previous high v. regime, suppression only occurs in a narrow RMP spectral window, indicating a resonant process, and a concomitant confinement drop is observed due to a reduction of pedestal top density and electron temperature. Strong evidence is found for the ion heat flux to be the decisive element for the L.H power threshold. A physics based scaling of the density at which the minimum PLH occurs indicates that ITER could take advantage of it to initiate H-mode at lower density than that of the finalQ = 10 operational point. Core density fluctuation measurements resolved in radius and wave number show that an increase of R/LT e introduced by off-axis electron cyclotron resonance heating (ECRH) mainly increases the large scale fluctuations. The radial variation of the fluctuation level is in agreement with simulations using the GENE code. Fast particles are shown to undergo classical slowing down in the absence of large scale magnetohydrodynamic (MHD) events and for low heating power, but show signs of anomalous radial redistribution at large heating power, consistent with a broadened off-axis neutral beam current drive current profile under these conditions. Neoclassical tearing mode (NTM) suppression experiments using electron cyclotron current drive (ECCD) with feedback controlled deposition have allowed to test several control strategies for ITER, including automated control of (3,2) and (2,1) NTMs during a single discharge. Disruption mitigation studies using massive gas injection (MGI) can show an increased fuelling efficiency with high field side injection, but a saturation of the fuelling efficiency is observed at high injected mass as needed for runaway electron suppression. Large locked modes can significantly decrease the fuelling efficiency and increase the asymmetry of radiated power during MGI mitigation. Concerning power exhaust, the partially detached ITER divertor scenario has been demonstrated at Psep/R = 10MWm.1 in ASDEX Upgrade, with a peak time averaged target load around 5MWm.2, well consistent with the component limits for ITER. Developing this towards DEMO, full detachment was achieved at Psep/R = 7MWm.1 and stationary discharges with core radiation fraction of the order of DEMO requirements (70% instead of the 30% needed for ITER) were demonstrated. Finally, it remains difficult to establish the standard ITERQ = 10 scenario at low q95 = 3 in the all-tungsten (all-W) ASDEX Upgrade due to the observed poor confinement at low βN. This is mainly due to a degraded pedestal performance and hence investigations at shifting the operational point to higher βN by lowering the current have been started. At higher q95, pedestal performance can be recovered by seeding N2 as well as CD4, which is interpreted as improved pedestal stability due to the decrease of bootstrap current with increasing Zeff . Concerning advanced scenarios, the upgrade of ECRH power has allowed experiments with central ctr-ECCD to modify the q-profile in improved H-mode scenarios, showing an increase in confinement at still good MHD stability with flat elevated q-profiles at values between 1.5 and 2. © 2015 EURATOM Printed in the UK. Source

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