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A new data access system, H1DS, has been developed and deployed for the H-1 Heliac at the Australian Plasma Fusion Research Facility. The data system provides access to fusion data via a RESTful web service. With the URL acting as the API to the data system, H1DS provides a scalable and extensible framework which is intuitive to new users, and allows access from any internet connected device. The H1DS framework, originally designed to work with MDSplus, has a modular design which can be extended to provide access to alternative data storage systems.

Large sub-millisecond heat pulses due to Type-I edge localized modes (ELMs) have been eliminated reproducibly in DIII-D for periods approaching nine energy confinement times (tau(E)) with small dc currents driven in a simple magnetic perturbation coil. The current required to eliminate all but a few isolated Type-l ELM impulses during a coil pulse is less than 0.4% of plasma current. Based on magnetic field line modelling, the perturbation fields resonate with plasma flux surfaces across most of the pedestal region (0.9 4-6 tau(E)) have been reproduced numerous times, on multiple experimental run days in high and intermediate triangularity plasmas, including cases matching the baseline ITER scenario 2 flux surface shape. In low triangularity, lower single null plasmas, with collisionalities near that expected in ITER, Type-l ELMs are replaced by small amplitude, high frequency Type-II-like ELMs and are often accompanied by one or more ELM-free periods approaching 1-2 tau(E). Large Type-I ELM impulses represent a severe constraint on the survivability of the divertor target plates in future burning plasma devices. Results presented in this paper demonstrate that non-axisymmetric edge magnetic perturbations provide a very attractive development path for active ELM control in future tokamaks such as ITER.

The H-1NF heliac is a medium-sized heliac stellarator experiment with major radius R = 1 m, and average plasma minor radius a = 0.15–0.2 m. Its ‘flexible-heliac’ coil set permits precise variation in the value and shape of the rotational transform (ι) profile, with regions of both positive and negative shear. Operation at low fields ( B< 0. 2T ) with argon plasmas heated by helicon waves produces plasmas that have large ion Larmor radii (ρi/a ∼ 0.4) and show confinement transitions at low power like those in the edge of large devices, yielding fundamental measurements concerning electric fields and zonal flows. At a higher field (0.5 T), precise rotational transform scans with H–He plasmas heated by ICRF show resonant equilibrium and stability phenomena which depend on the value of the rotational transform at the radius of zero shear.

The H-1NF heliac regularly operates using the ion cyclotron range of frequencies at 0.5 T to produce plasmas with a mixture of hydrogen and helium gases. Due to the complex three-dimensional structure of the magnetic fluxsurfaces, these plasmas require sophisticated diagnostic systems, with good spatial coverage, to extract meaningful physical information. This article presents a study of the dependence of the plasma density profile on resonant heating conditions and magnetic configuration, using a far-infrared scanning interferometer. Recent modifications to the system and data that illustrate the performance of the interferometer will be discussed.

We present a data mining technique for the analysis of multichannel oscillatory timeseries data and show an application using poloidal arrays of magnetic sensors installed in the H-1 heliac. The procedure is highly automated, and scales well to large datasets. The timeseries data is split into short time segments to provide time resolution, and each segment is represented by a singular value decomposition (SVD). By comparing power spectra of the temporal singular vectors, singular values are grouped into subsets which define fluctuation structures. Thresholds for the normalised energy of the fluctuation structure and the normalised entropy of the SVD are used to filter the dataset. We assume that distinct classes of fluctuations are localised in the space of phase differences between each pair of nearest neighbour channels. An expectation maximisation clustering algorithm is used to locate the distinct classes of fluctuations, and a cluster tree mapping is used to visualise the results., Comment: 14 pages, 8 figures

OAK-B135 A stochastic magnetic boundary, produced by an externally applied edge resonant magnetic perturbation, is used to suppress large edge localized modes (ELMs) in high confinement (H-mode) plasmas. The resulting H-mode displays rapid, small oscillations with a bursty character modulated by a coherent 130 Hz envelope. The H-mode transport barrier is unaffected by the stochastic boundary. The core confinement of these discharges is unaffected, despite a three-fold drop in the toroidal rotation in the plasma core. These results demonstrate that stochastic boundaries are compatible with H-modes and may be attractive for ELM control in next-step burning fusion tokamaks.

We present an analysis of empirically derived basis vectors for feature detection in radial profile data. Our aim is to classify broad and peaked profiles using unsupervised techniques. Radial data often contains a continuum of profile shapes from broad to peaked, as such clustering methods may be unreliable. Previously, ad hoc heuristic measures had been used for classification of profiles from raw data (without tomographic reconstruction), which required significant manual inspection of the data. Here, we apply a singular value decomposition (SVD) to a training data matrix consisting of a concatenation of multichannel bolometry time series data from 103 TJ-II plasma discharges with good representation of the range of profiles. The second largest spatial basis vector (topo) has radial roots either side of the plasma centre, and can intuitively be interpreted as a peakedness perturbation. The inverted topo matrix can be used to process new data for automated profile classification. Finally, we show an application of this method using support vector machines to locate other signals related to the radiation profile.

The need to understand the structure of magnetic fluctuations in H-1NF heliac [S. Hamberger et al., Fusion Technol. 17, 123 (1990)] plasmas has motivated the installation of a sixteen former, tri-axis helical magnetic probe Mirnov array (HMA). The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and improved toroidal resolution. The helical placement is ideal for helical axis plasmas because it positions the array as close as possible to the plasma in regions of varying degrees of favourable curvature in the magnetohydrodynamic sense, but almost constant magnetic angle. This makes phase variation with probe position near linear, greatly simplifying the analysis of the data. Several of the issues involved in the design, installation, data analysis, and calibration of this unique array are presented including probe coil design, frequency response measurements, mode number identification, orientation calculations, and mapping probe coil positions to magnetic coordinates. Details of specially designed digitally programmable pre-amplifiers, which allow gains and filters to be changed as part of the data acquisition initialisation sequence and stored with the probe signals, are also presented. The low shear heliac geometry [R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011)], flexibility of the H-1NF heliac, and wealth of information provided by the HMA create a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious issue for future fusion reactors.

We extend a reduced-dimension stellarator ideal-MHD normal-mode model to include a vacuum region, and describe magnetic fluctuations in the H-1 heliac. We apply the reduced model to a magnetic field configuration with high density and compute the two lowest frequency global Alfven eigenmodes (GAEs): (m, n) = (4, 5) and (7, 9). The poloidal mode number, predicted frequency and radial attenuation profile are then compared with measurements from a poloidal Mirnov array. Of the two candidates, the (7, 9) mode has a closer match in frequency and radial attenuation profile, and its narrower radial eigenfunction is a better match to recent optical-emission measurements [18]. Measurements of the temporal evolution of the mode are also consistent with the inferred Alfven frequency scaling at the radial localization of the (7, 9) mode. Combined, these observations suggest the measured fluctuation is a (7, 9) GAE. A wider benefit of our work includes the potential of a reduced-dimension normal-mode MHD model, with negligible computational needs, to characterize and identify mode activity in real time based on frequency, phase information, internal measurements and vacuum region attenuation. Such a model, which is likely to improve in accuracy for devices with simpler configuration such as a tokamak, may be useful as a tool for real time MHD spectroscopy, and to predict and control global eigenmodes associated with fast ion loss in burning plasmas.

High frequency modes (150-300 kHz) are found in several magnetic configurations of TJ-II plasmas heated by neutral beam injection (NBI). The clear dependence of mode frequency on plasma density and mass species suggests them to be Alfveigenmodes. The appearance of these modes is linked to the presence of low order rational surfaces close to the rotational transform profile. They can exhibit steady or chirping behaviour depending on the plasma profiles. Frequency chirping is observed in NBI plasmas with broad temperature profiles, but rarely observed with relatively peaked profiles. The Alfvactivity has been characterized in detail with magnetic coils for the standard configuration. Cross analyses with heavy ion beam probe and reflectometer signals have yielded spatial resolution and radial profiles of the perturbation. Correlation between magnetic coil signals and signals from diagnostics sensitive to edge ion losses, namely Langmuir probes and a fast ion loss detector, has been observed in some cases and characterized taking advantage of the chirping nature of the observed Alfvactivity. (Some figures in this article are in colour only in the electronic version)

Recently, bayesian probability theory has been used at a number of experiments to fold uncertainties and interdependencies in the diagnostic data and forward models, together with prior knowledge of the state of the plasma, to increase accuracy of inferred physics variables. A new probabilistic framework, MINERVA, based on bayesian graphical models, has been used at JET and W7-AS to yield predictions of internal magnetic structure. A feature of the framework is the bayesian inversion for poloidal magnetic flux without the need for an explicit equilibrium assumption. Building on this, we discuss results from a new project to develop bayesian inversion tools that aim to (1) distinguish between competing equilibrium theories, which capture different physics, using the MAST spherical tokamak, and (2) test the predictions of MHD theory, particularly mode structure, using the H-1 Heliac. Specifically, we report on correction of the motional Stark effect, pickup coils, flux-loop constrained bayesian inferred equilibrium for varying toroidal flux.

Data mining techniques, which automatically extract useful knowledge from large datasets, are applied to multichannel magnetic probe signals of several helical plasmas in order to identify and classify MHD instabilities in helical plasmas. This method is useful to find new MHD instabilities as well as previously identified ones. Moreover, registering the results obtained from data mining in a database allows us to investigate the characteristics of MHD instabilities with parameter studies. We introduce the data mining technique consisted of pre-processing, clustering and visualizations using results from helical plasmas in H-1 and Heliotron J. We were successfully able to classify the MHD instabilities using the criterion of phase differences of each magnetic probe and identify them as energetic-ion-driven MHD instabilities using parameter study in Heliotron J plasmas.

We develop a practical, structured analysis of multi-channel time series measurements where the main interest lies in the coherent temporal fluctuations and spatial structures and their time dependence. The current approach to most large scale plasma experiments, tokamak and stellarators alike, is the quest for the experimental data taken under optimal conditions for each study. These data are then analysed in detail and sometimes distributed in a reference database such as the tokamak profile database of the ITER 1D Modelling Working Group. While these results are important for our understanding of future fusion devices, they do not provide easy means to support the evidence based on statistical ensembles. The raw data which are not accessible to simple search queries, are usually kept in large data repositories. At H-1, we routinely log the global experimental parameters in a summary database which is stored in a easily accessible database. In order to facilitate statistical analysis and the search for a wide class of magnetic phenomena, we developed a data processing procedure that reduces the raw signal of an array of Mirnov coils at the H-1 into a series of feature descriptors in time-frequency space which are stored in an SQL-accessible database, which can be used together with the summary database. References R. S. Anderssen, F. De Hoog, and M. Hegland, A stable finite difference ansatz for higher order differentiation of non-exact data , Bull. Austral. Math. Soc. 58 (1998), 223--232. S. Beucher, The watershed transformation applied to image segmentation , Conference on Signal and Image Processing in Microscopy and Microanalysis, September 1991, pp. 299--314. T. Dudok de Witt, Enhancement of multichannel data in plasma physics by biorthogonal decomposition, Plasma Physics and Controlled Fusion 37 (1995), no. 2, 117--135, http://stacks.iop.org/0741-3335/37/117 . G. H. Golub and C. F. Van Loan, Matrix computations , third ed., Johns Hopkins Studies in the Mathematical Sciences, Johns Hopkins University Press, Baltimore, MD, 1996. MR1417720 (97g:65006) J. H. Harris, M. G. Shats, B. D. Blackwell, W. M. Solomon, D. G. Pretty, S. M. Collis, J. Howard, H. Xia, C. A. Michael, and H. Punzmann, Fluctuations and stability of plasmas in the H-1NF heliac, Nucl. Fusion 44 (2004), 279, doi:10.1088/0029-5515/44/2/008 . T. Hastie, R. Tibshirani, and J. H. Friedman, The elements of statistical learning , Springer, August 2001. M. Hegland and R. S. Anderssen, Resolution enhancement of spectra using differentiation, Inverse Problems 21 (2005), no. 3, 915--934, http://stacks.iop.org/0266-5611/21/915 . C. Nardone, Multichannel fluctuation data analysis by the singular value decomposition method. Application to MHD modes in JET, Plasma Physics and Controlled Fusion 34 (1992), no. 9, 1447--1465, http://stacks.iop.org/0741-3335/34/1447 . A. Rosenfeld and J. L. Pfaltz, Sequential operations in digital picture processing, J. Assoc. Comp. Mach. 13 (1966), 471--494, doi:10.1145/321356.321357 . J. Serra, Image analysis and mathematical morphology , Academic Press, Inc., Orlando, FL, USA, 1983. O. Skylar and W. Huber, Image analysis for microscopy screens: Image analysis and processing with EBIimage, R. News 6 (2006), no. 5, 1215, http://CRAN.R-project.org/doc/Rnews/Rnews_2006-5.pdf . R. Stening, T. Reztsova, D. Ivers, J. Turner, and D. Winch, Morning quiet-time ionospheric current reversal at mid to high latitudes, Annales Geophysicae 23 (2005), 385, http://adsabs.harvard.edu/abs/2005AnGeo..23..385S . "The ITER 1D Modelling Working Group", D. Boucher, J. W. Connor, W. A. Houlberg, M. F. Turner, G. Bracco, A. Chudnovskiy, J. G. Cordey, M. J. Greenwald, G. T. Hoang, G. M. D. Hogeweij, S. M. Kaye, J. E. Kinsey, D. R. Mikkelsen, J. Ongena, D. R. Schissel, H. Shirai, J. Stober, P. M. Stubberfield, R. E. Waltz, and J. Weiland, The international multi-tokamak profile database, Nuclear Fusion 40 (2000), no. 12, 1955--1981, http://stacks.iop.org/0029-5515/40/1955 . S. Whitehouse, Magick with images, Linux J. (1998), 7, http://www.linuxjournal.com/article/2707 .

This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma–wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z, Li was chosen because there exists a reactor-oriented interest in this element, thus giving special relevance to the investigation of its properties. The Li-coating has led to important changes in plasma performance. Particularly, the effective density limit in NBI plasmas has been extended reaching central values of 8 × 1019 m−3 and T e ≈ 250–300 eV, with peaked density, rather flat T e profiles and higher ion temperatures. Due to the achieved density control, a second type of transition has been added to the low density ones previously observed in ECRH plasmas: higher density transitions characterized by the fall in Hα emission, the onset of steep density gradient and the reduction in the turbulence; which are characteristics of transition to the H mode. Confinement studies in ECH plasmas indicate that lowest order magnetic resonances, even in a low shear environment, locally reduce the effective electron heat diffusivities, while Alfven eigenmodes destabilized in NBI plasmas can influence fast ion confinement.

The H‐1 heliac has been substantially upgraded under the Australian Government’s Major National Research Facility Program. Enhancements include precision magnet power supplies, a 250kW RF source, and a 200kW 28GHz ECH system in collaboration with NIFS and Kyoto University. The power supply allows operation to fields ∼1 T with computer‐controlled configurations, and ripple 20eV) in this mode. In many cases, probe and spectroscopic results indicate that in these plasmas, the mass flow velocities are less than the E×B velocity. Correlation studies of probe and spectroscopic data yield important information about flow structures in these plasmas. At 0.5 tesla, RF (20 ∼150kW, ω ∼ ωcH) produces plasma in H:He and H:D mixtures at densities up to 〈ne〉 ∼ 2×1018m−3, with temperatures initially limited to < 50eV by low‐Z impurities. ECH (ω = 2ωce) produces considerably higher temperatures and centrally‐peaked density profiles. Magnetic configuration scans show a strong, detailed dependence of plasma density on rotational transform. Magnetic fluctuations are stronger in RF‐produced plasma, and spectra depend on magnetic configuration.