Sawtooth instabilities can modify heating and current-drive profiles and potentially increase fast-ion losses. Understanding how sawteeth redistribute fast ions as a function of sawtooth parameters and of fast-ion energy and pitch is hence a subject of particular interest for future fusion devices. Here we present the first collective Thomson scattering (CTS) measurements of sawtooth-induced redistribution of fast ions at ASDEX Upgrade. These also represent the first localized fast-ion measurements on the high-field side of this device. The results indicate fast-ion losses in the phase-space measurement volume of about 50% across sawtooth crashes, in good agreement with values predicted with the Kadomtsev sawtooth model implemented in TRANSP and with the sawtooth model in the EBdyna_go code. In contrast to the case of sawteeth, we observe no fast-ion redistribution in the presence of fishbone modes. We highlight how CTS measurements can discriminate between different sawtooth models, in particular when aided by multi-diagnostic velocity-space tomography, and briefly discuss our results in light of existing measurements from other fast-ion diagnostics.

VL - 56 UR - http://www.euro-fusionscipub.org/wp-content/uploads/eurofusion/WPMST1PR16_14817_submitted.pdf IS - 11 U1 -FP

U2 -IMM

U3 - FP120 U5 - eddb183650ee17cb3ca57e0115ea119f ER - TY - JOUR T1 - Doppler tomography in fusion plasmas and astrophysics JF - Plasma Physics and Controlled Fusion Y1 - 2015 A1 - Salewski, M. A1 - Geiger, B. A1 - Heidbrink, W. W. A1 - Jacobsen, A. S. A1 - Korsholm, S. B. A1 - Leipold, F. A1 - Madsen, J. A1 - Moseev, D. A1 - Nielsen, S.K. A1 - Rasmussen, J. A1 - Stagner, L. A1 - Steeghs, D. A1 - Stejner, M. A1 - Tardini, G. A1 - Weiland, M. A1 - ASDEX Upgrade Team AB - Doppler tomography is a well-known method in astrophysics to image the accretion flow, often in the shape of thin discs, in compact binary stars. As accretion discs rotate, all emitted line radiation is Doppler-shifted. In fast-ion D-alpha (FIDA) spectroscopy measurements in magnetically confined plasma, the D-alpha-photons are likewise Doppler-shifted ultimately due to gyration of the fast ions. In either case, spectra of Doppler-shifted line emission are sensitive to the velocity distribution of the emitters. Astrophysical Doppler tomography has lead to images of accretion discs of binaries revealing bright spots, spiral structures and flow patterns. Fusion plasma Doppler tomography has led to an image of the fast-ion velocity distribution function in the tokamak ASDEX Upgrade. This image matched numerical simulations very well. Here we discuss achievements of the Doppler tomography approach, its promise and limits, analogies and differences in astrophysical and fusion plasma Doppler tomography and what can be learned by comparison of these applications. VL - 57 IS - 1 U1 - FP U2 - PDG U5 - 38c10f70990ab1c69b90b6c29b6a1213 ER - TY - JOUR T1 - Measurements of the fast-ion distribution function at ASDEX upgrade by collective Thomson scattering (CTS) using active and passive views JF - Plasma Physics and Controlled Fusion Y1 - 2015 A1 - Nielsen, S.K. A1 - Stejner, M. A1 - Rasmussen, J. A1 - Jacobsen, A. S. A1 - Korsholm, S. B. A1 - Leipold, F. A1 - Maraschek, M. A1 - Meo, F. A1 - Michelsen, P. K. A1 - Moseev, D. A1 - Salewski, M. A1 - Schubert, M. A1 - Stober, J. A1 - Suttrop, W. A1 - Tardini, G. A1 - Wagner, D. AB - Collective Thomson scattering (CTS) can provide measurements of the confined fast-ion distribution function resolved in space, time and 1D velocity space. On ASDEX Upgrade, the measured spectra include an additional signal which previously has hampered data interpretation. A new set-up using two independent heterodyne receiver systems enables subtraction of the additional part from the total spectrum, revealing the resulting CTS spectrum. Here we present CTS measurements from the plasma centre obtained in L-mode and H-mode plasmas with and without neutral beam injection (NBI). For the first time, the measured spectra agree quantitatively with the synthetic spectra in periods with and without NBI heating. For the discharges investigated, the central velocity distribution of neutral beam ions can be described by classical slowing down. These results will have a major impact on ITER physics exploration, since CTS is presently the only diagnostic to measure the confined alpha particles produced by the fusion reactions. VL - 57 IS - 3 U1 - FP U2 - PDG U5 - 428c8b386186e809125a64e543a5c5b2 ER - TY - JOUR T1 - On velocity-space sensitivity of fast-ion D-alpha spectroscopy JF - Plasma Physics and Controlled Fusion Y1 - 2014 A1 - Salewski, M. A1 - Geiger, B. A1 - Moseev, D. A1 - Heidbrink, W. W. A1 - Jacobsen, A. S. A1 - Korsholm, S. B. A1 - Leipold, F. A1 - Madsen, J. A1 - Nielsen, S.K. A1 - Rasmussen, J. A1 - Stejner, M. A1 - Weiland, M. A1 - ASDEX Upgrade Team AB - The velocity-space observation regions and sensitivities in fast-ion D α (FIDA) spectroscopy measurements are often described by so-called weight functions. Here we derive expressions for FIDA weight functions accounting for the Doppler shift, Stark splitting, and the charge-exchange reaction and electron transition probabilities. Our approach yields an efficient way to calculate correctly scaled FIDA weight functions and implies simple analytic expressions for their boundaries that separate the triangular observable regions in ( v ‖ , v ⊥ )-space from the unobservable regions. These boundaries are determined by the Doppler shift and Stark splitting and could until now only be found by numeric simulation. VL - 56 IS - 10 U1 - FP U2 - PDG U5 - b72cfc9a9e4bf3b78b16c6a66f09083c ER - TY - JOUR T1 - Experimental characterization of anomalous strong scattering of mm-waves in TEXTOR plasmas with rotating islands JF - Plasma Physics and Controlled Fusion Y1 - 2013 A1 - Nielsen, S.K. A1 - Salewski, M. A1 - Westerhof, E. A1 - Bongers, W. A1 - Korsholm, S. B. A1 - Leipold, F. A1 - Oosterbeek, J. W. A1 - Moseev, D. A1 - Stejner, M. A1 - TEXTOR team AB -Anomalous scattering of high power millimetre waves from gyrotrons at 140 and 110 GHz is investigated for plasma with rotating islands at TEXTOR. The magnetic field and plasma density influence the spectral content of the scattered waves and their power levels significantly. Anomalous strong scattering occurs in two density regimes, one at low densities and one at high densities, that also depend on the magnetic field. The two regimes are separated by a quiescent regime without anomalous scattering. Investigations suggest that scattering in the high-density regime is generated at the low-field side intersection of the gyrotron beam and the island position. The transition from the quiescent regime to the high-density regime occurs when the gyrotron frequency is twice the upper hybrid frequency at this position. There is some evidence that the scattering in the low-density regime is generated near the plasma centre. Under this assumption all the observed scattering is generated when the gyrotron frequency is near or below twice the upper hybrid frequency.

VL - 55 U1 -FP

U2 -CPP-HT

U5 - e2ed3d6c806820f4af5c05b69975f955 ER - TY - JOUR T1 - Overview of ASDEX Upgrade results JF - Nuclear Fusion Y1 - 2013 A1 - Stroth, U. A1 - Adamek, J. A1 - Aho-Mantila, L. A1 - Akaslompolo, S. A1 - Amdor, C. A1 - Angioni, C. A1 - Balden, M. A1 - Bardin, S. A1 - L. Barrera Orte A1 - Behler, K. A1 - Belonohy, E. A1 - Bergmann, A. A1 - Bernert, M. A1 - Bilato, R. A1 - Birkenmeier, G. A1 - Bobkov, V. A1 - Boom, J. A1 - Bottereau, C. A1 - Bottino, A. A1 - Braun, F. A1 - Brezinsek, S. A1 - Brochard, T. A1 - M. Brüdgam A1 - Buhler, A. A1 - Burckhart, A. A1 - Casson, F. J. A1 - Chankin, A. A1 - Chapman, I. A1 - Clairet, F. A1 - Classen, I.G.J. A1 - Coenen, J. W. A1 - Conway, G. D. A1 - Coster, D. P. A1 - Curran, D. A1 - da Silva, F. A1 - P. de Marné A1 - D'Inca, R. A1 - Douai, D. A1 - Drube, R. A1 - Dunne, M. A1 - Dux, R. A1 - Eich, T. A1 - Eixenberger, H. A1 - Endstrasser, N. A1 - Engelhardt, K. A1 - Esposito, B. A1 - Fable, E. A1 - Fischer, R. A1 - H. Fünfgelder A1 - Fuchs, J. C. A1 - K. Gál A1 - M. García Muñoz A1 - Geiger, B. A1 - Giannone, L. A1 - T. Görler A1 - da Graca, S. A1 - Greuner, H. A1 - Gruber, O. A1 - Gude, A. A1 - Guimarais, L. A1 - S. Günter A1 - Haas, G. A1 - Hakola, A. H. A1 - Hangan, D. A1 - Happel, T. A1 - T. Härtl A1 - Hauff, T. A1 - Heinemann, B. A1 - Herrmann, A. A1 - Hobirk, J. A1 - H. Höhnle A1 - M. Hölzl A1 - Hopf, C. A1 - Houben, A. A1 - Igochine, V. A1 - Ionita, C. A1 - Janzer, A. A1 - Jenko, F. A1 - Kantor, M. A1 - C.-P. Käsemann A1 - Kallenbach, A. A1 - S. Kálvin A1 - Kantor, M. A1 - Kappatou, A. A1 - Kardaun, O. A1 - Kasparek, W. A1 - Kaufmann, M. A1 - Kirk, A. A1 - H.-J. Klingshirn A1 - Kocan, M. A1 - Kocsis, G. A1 - Konz, C. A1 - Koslowski, R. A1 - Krieger, K. A1 - Kubic, M. A1 - Kurki-Suonio, T. A1 - Kurzan, B. A1 - Lackner, K. A1 - Lang, P. T. A1 - Lauber, P. A1 - Laux, M. A1 - Lazaros, A. A1 - Leipold, F. A1 - Leuterer, F. A1 - Lindig, S. A1 - Lisgo, S. A1 - Lohs, A. A1 - Lunt, T. A1 - Maier, H. A1 - Makkonen, T. A1 - Mank, K. A1 - M.-E. Manso A1 - Maraschek, M. A1 - Mayer, M. A1 - McCarthy, P. J. A1 - McDermott, R. A1 - Mehlmann, F. A1 - Meister, H. A1 - Menchero, L. A1 - Meo, F. A1 - Merkel, P. A1 - Merkel, R. A1 - Mertens, V. A1 - Merz, F. A1 - Mlynek, A. A1 - Monaco, F. A1 - Müller, S. A1 - H.W. Müller A1 - M. Münich A1 - Neu, G. A1 - Neu, R. A1 - Neuwirth, D. A1 - Nocente, M. A1 - Nold, B. A1 - Noterdaeme, J. M. A1 - Pautasso, G. A1 - Pereverzev, G. A1 - B. Plöckl A1 - Podoba, Y. A1 - Pompon, F. A1 - Poli, E. A1 - Polozhiy, K. A1 - Potzel, S. A1 - Puschel, M. J. A1 - Putterich, T. A1 - Rathgeber, S. K. A1 - Raupp, G. A1 - Reich, M. A1 - Reimold, F. A1 - Ribeiro, T. A1 - Riedl, R. A1 - Rohde, V. A1 - G. J. van Rooij A1 - Roth, J. A1 - Rott, M. A1 - Ryter, F. A1 - Salewski, M. A1 - Santos, J. A1 - Sauter, P. A1 - Scarabosio, A. A1 - Schall, G. A1 - Schmid, K. A1 - Schneider, P. A. A1 - Schneider, W. A1 - Schrittwieser, R. A1 - Schubert, M. A1 - Schweinzer, J. A1 - Scott, B. A1 - Sempf, M. A1 - Sertoli, M. A1 - Siccinio, M. A1 - Sieglin, B. A1 - Sigalov, A. A1 - Silva, A. A1 - Sommer, F. A1 - A. Stäbler A1 - Stober, J. A1 - Streibl, B. A1 - Strumberger, E. A1 - Sugiyama, K. A1 - Suttrop, W. A1 - Tala, T. A1 - Tardini, G. A1 - Teschke, M. A1 - Tichmann, C. A1 - Told, D. A1 - Treutterer, W. A1 - Tsalas, M. A1 - VanZeeland, M. A. A1 - Varela, P. A1 - Veres, G. A1 - Vicente, J. A1 - Vianello, N. A1 - Vierle, T. A1 - Viezzer, E. A1 - Viola, B. A1 - Vorpahl, C. A1 - Wachowski, M. A1 - Wagner, D. A1 - Wauters, T. A1 - Weller, A. A1 - Wenninger, R. A1 - Wieland, B. A1 - Willensdorfer, M. A1 - Wischmeier, M. A1 - Wolfrum, E. A1 - E. Würsching A1 - Yu, Q. A1 - Zammuto, I. A1 - Zasche, D. A1 - Zehetbauer, T. A1 - Zhang, Y. A1 - Zilker, M. A1 - Zohm, H. AB - The medium size divertor tokamak ASDEX Upgrade (major and minor radii 1.65 m and 0.5 m, respectively, magnetic-field strength 2.5 T) possesses flexible shaping and versatile heating and current drive systems. Recently the technical capabilities were extended by increasing the electron cyclotron resonance heating (ECRH) power, by installing 2 × 8 internal magnetic perturbation coils, and by improving the ion cyclotron range of frequency compatibility with the tungsten wall. With the perturbation coils, reliable suppression of large type-I edge localized modes (ELMs) could be demonstrated in a wide operational window, which opens up above a critical plasma pedestal density. The pellet fuelling efficiency was observed to increase which gives access to H-mode discharges with peaked density profiles at line densities clearly exceeding the empirical Greenwald limit. Owing to the increased ECRH power of 4 MW, H-mode discharges could be studied in regimes with dominant electron heating and low plasma rotation velocities, i.e. under conditions particularly relevant for ITER. The ion-pressure gradient and the neoclassical radial electric field emerge as key parameters for the transition. Using the total simultaneously available heating power of 23 MW, high performance discharges have been carried out where feed-back controlled radiative cooling in the core and the divertor allowed the divertor peak power loads to be maintained below 5 MW m −2 . Under attached divertor conditions, a multi-device scaling expression for the power-decay length was obtained which is independent of major radius and decreases with magnetic field resulting in a decay length of 1 mm for ITER. At higher densities and under partially detached conditions, however, a broadening of the decay length is observed. In discharges with density ramps up to the density limit, the divertor plasma shows a complex behaviour with a localized high-density region in the inner divertor before the outer divertor detaches. Turbulent transport is studied in the core and the scrape-off layer (SOL). Discharges over a wide parameter range exhibit a close link between core momentum and density transport. Consistent with gyro-kinetic calculations, the density gradient at half plasma radius determines the momentum transport through residual stress and thus the central toroidal rotation. In the SOL a close comparison of probe data with a gyro-fluid code showed excellent agreement and points to the dominance of drift waves. Intermittent structures from ELMs and from turbulence are shown to have high ion temperatures even at large distances outside the separatrix. VL - 53 UR - http://hdl.handle.net/11858/00-001M-0000-0026-E166-7 IS - 10 U1 - FP U2 - PDG U5 - 0b5b08fdc590c85cc01e6d1db1958848 ER - TY - JOUR T1 - Combination of fast-ion diagnostics in velocity-space tomographies JF - Nuclear Fusion Y1 - 2013 A1 - Salewski, M. A1 - Geiger, B. A1 - Nielsen, S.K. A1 - Bindslev, H. A1 - M. García-Muñoz A1 - Heidbrink, W. W. A1 - Korsholm, S. B. A1 - Leipold, F. A1 - Madsen, J. A1 - Meo, F. A1 - Michelsen, P. K. A1 - Moseev, D. A1 - Stejner, M. A1 - Tardini, G. A1 - ASDEX Upgrade Team AB - Fast-ion D α (FIDA) and collective Thomson scattering (CTS) diagnostics provide indirect measurements of fast-ion velocity distribution functions in magnetically confined plasmas. Here we present the first prescription for velocity-space tomographic inversion of CTS and FIDA measurements that can use CTS and FIDA measurements together and that takes uncertainties in such measurements into account. Our prescription is general and could be applied to other diagnostics. We demonstrate tomographic reconstructions of an ASDEX Upgrade beam ion velocity distribution function. First, we compute synthetic measurements from two CTS views and two FIDA views using a TRANSP/NUBEAM simulation, and then we compute joint tomographic inversions in velocity-space from these. The overall shape of the 2D velocity distribution function and the location of the maxima at full and half beam injection energy are well reproduced in velocity-space tomographic inversions, if the noise level in the measurements is below 10%. Our results suggest that 2D fast-ion velocity distribution functions can be directly inferred from fast-ion measurements and their uncertainties, even if the measurements are taken with different diagnostic methods. VL - 53 UR - http://stacks.iop.org/0029-5515/53/i=6/a=063019 U1 - FP U2 - PDG U5 - 23553dfb974e7824d2430fb92cca1052 ER - TY - JOUR T1 - Measurements of ion temperature and plasma hydrogenic composition by collective Thomson scattering in neutral beam heated discharges at TEXTOR JF - Plasma Physics and Controlled Fusion Y1 - 2013 A1 - Stejner, M. A1 - Salewski, M. A1 - Korsholm, S. B. A1 - Bindslev, H. A1 - Delabie, E. A1 - Leipold, F. A1 - Meo, F. A1 - Michelsen, P. K. A1 - Moseev, D. A1 - Nielsen, S.K. A1 - Burger, A. A1 - de M. Baar A1 - TEXTOR team AB - A method is developed to perform plasma composition and ion temperature measurements across the plasma minor radius in TEXTOR based on ion cyclotron structures in collective Thomson scattering spectra. By gradually moving the scattering volume, we obtain measurements across the outer midplane of the plasma. Results for the ion temperature are compared with ion temperatures measured by active charge-exchange recombination spectroscopy. VL - 55 UR - http://stacks.iop.org/0741-3335/55/i=8/a=085002 U1 - FP U2 - TP U5 - 0bfe671b2f929ad861e1fa7f8fdefa93 ER - TY - JOUR T1 - Tomography of fast-ion velocity-space distributions from synthetic CTS and FIDA measurements JF - Nuclear Fusion Y1 - 2012 A1 - Salewski, M. A1 - Geiger, B. A1 - Nielsen, S.K. A1 - Bindslev, H. A1 - M. García-Muñoz A1 - Heidbrink, W. W. A1 - Korsholm, S. B. A1 - Leipold, F. A1 - Meo, F. A1 - Michelsen, P. K. A1 - Moseev, D. A1 - Stejner, M. A1 - Tardini, G. KW - ALPHA KW - TOKAMAK KW - X-RAY TOMOGRAPHY AB - We compute tomographies of 2D fast-ion velocity distribution functions from synthetic collective Thomson scattering (CTS) and fast-ion D-alpha (FIDA) 1D measurements using a new reconstruction prescription. Contradicting conventional wisdom we demonstrate that one single 1D CTS or FIDA view suffices to compute accurate tomographies of arbitrary 2D functions under idealized conditions. Under simulated experimental conditions, single-view tomographies do not resemble the original fast-ion velocity distribution functions but nevertheless show their coarsest features. For CTS or FIDA systems with many simultaneous views on the same measurement volume, the resemblance improves with the number of available views, even if the resolution in each view is varied inversely proportional to the number of views, so that the total number of measurements in all views is the same. With a realistic four-view system, tomographies of a beam ion velocity distribution function at ASDEX Upgrade reproduce the general shape of the function and the location of the maxima at full and half injection energy of the beam ions. By applying our method to real many-view CTS or FIDA measurements, one could determine tomographies of 2D fast-ion velocity distribution functions experimentally. VL - 52 SN - 0029-5515 IS - 10 U1 - FP U2 - PDG U5 - 2ba49eb1441e838e1b4b1429134d2e12 ER - TY - JOUR T1 - Measurements of plasma composition in the TEXTOR tokamak by collective Thomson scattering JF - Plasma Physics and Controlled Fusion Y1 - 2012 A1 - Stejner, M. A1 - Korsholm, S. B. A1 - Nielsen, S.K. A1 - Salewski, M. A1 - Bindslev, H. A1 - Brezinsek, S. A1 - Furtula, V. A1 - Leipold, F. A1 - Michelsen, P. K. A1 - Meo, F. A1 - Moseev, D. A1 - Burger, A. A1 - Kantor, M. A1 - M.R. de Baar KW - diagnostics KW - ION-TEMPERATURE-MEASUREMENT KW - LASER SCATTERING KW - RADIATION KW - SCENARIOS KW - WAVES AB - We demonstrate the use of collective Thomson scattering (CTS) for spatially localized measurements of the isotopic composition of magnetically confined fusion plasmas. The experiments were conducted in the TEXTOR tokamak by scattering millimeter-wave probe radiation off plasma fluctuations with wave vector components nearly perpendicular to the magnetic field. Under such conditions the sensitivity of the CTS spectrum to plasma composition is enhanced by the spectral signatures of the ion cyclotron motion and of weakly damped ion Bernstein waves. Recent experiments on TEXTOR demonstrated the ability to resolve these signatures in the CTS spectrum as well as their sensitivity to the ion species mix in the plasma. This paper shows that the plasma composition can be inferred from the measurements through forward modeling of the CTS spectrum. We demonstrate that spectra measured in plasmas consisting of hydrogen, deuterium and (3)He can be accurately reproduced by theory and yield inferred plasma compositions consistent with expectations. The potential to use CTS for measurements of plasma composition is of significant interest since CTS is well suited for reactor environments and since there is at present no established method to measure the fuel ion density ratio in the core of a burning fusion plasma. VL - 54 SN - 0741-3335 IS - 1 U1 - FP U2 - PDG U5 - 44bb7848240e89f8394b5e6254e79db4 ER - TY - JOUR T1 - Modification of the collective Thomson scattering radiometer in the search for parametric decay on TEXTOR JF - Review of Scientific Instruments Y1 - 2012 A1 - Nielsen, S.K. A1 - Salewski, M. A1 - Bongers, W. A. A1 - Korsholm, S. B. A1 - Leipold, F. A1 - Meo, F. A1 - Michelsen, P. A1 - Moseev, D. A1 - Oosterbeek, J. W. A1 - Stejner, M. A1 - Westerhof, E. KW - electromagnetic wave scattering KW - millimetre waves KW - plasma diagnostics KW - radiometers PB - AIP VL - 83 UR - http://link.aip.org/link/?RSI/83/113508/1 IS - 11 U1 - FP U2 - TP U5 - 11392b9249c371579918a643dc83dd7f ER - TY - JOUR T1 - Elevation angle alignment of quasi optical receiver mirrors of collective Thomson scattering diagnostic by sawtooth measurements JF - Review of Scientific Instruments Y1 - 2012 A1 - Moseev, D. A1 - Meo, F. A1 - Korsholm, S. B. A1 - Bindslev, H. A1 - Furtula, V. A1 - Kantor, M. A1 - Leipold, F. A1 - Michelsen, P. K. A1 - Nielsen, S.K. A1 - Salewski, M. A1 - Stejner, M. KW - mirrors KW - optical receivers KW - plasma diagnostics KW - plasma oscillations KW - plasma toroidal confinement KW - plasma transport processes KW - Tokamak devices KW - transmission lines PB - AIP VL - 83 UR - http://link.aip.org/link/?RSI/83/10E337/1 U1 - FP U2 - PDG U5 - ec1a50751b573776a50bbdf5b5ddce8e ER - TY - JOUR T1 - Performance measurements of the collective Thomson scattering receiver at ASDEX Upgrade JF - Journal of Instrumentation Y1 - 2012 A1 - Furtula, V. A1 - Leipold, F. A1 - Salewski, M. A1 - Michelsen, P. K. A1 - Korsholm, S. B. A1 - Meo, F. A1 - Moseev, D. A1 - Nielsen, S.K. A1 - Stejner, M. A1 - T Johansen AB - The fast-ion collective Thomson scattering (CTS) receiver at ASDEX Upgrade can detect spectral power densities of a few eV in the millimeter-wave range against the electron cyclotron emission (ECE) background on the order of 100 eV under presence of gyrotron stray radiation that is several orders of magnitude stronger than the signal to be detected. The receiver heterodynes the frequencies of scattered radiation (100–110 GHz) to intermediate frequencies (IF) (4.5–14.5 GHz). The IF signal is divided into 50 IF channels tightly spaced in frequency space which are terminated by square-law Schottky detector diodes. The performance of the entire receiver is determined by the main receiver components operating at mm-wave frequencies (notch-, bandpass- and lowpass filters, a voltage-controlled variable attenuator, and an isolator), a mixer, and the IF components (amplifiers, band-pass filters, and detector diodes). We discuss here the design of the entire receiver, focussing on its performance as a unit. The receiver has been disassembled, and the performance of its individual components has been characterized. Based on these individual component measurements we predict the spectral response of the receiver assembled as a unit. The measured spectral response of the assembled receiver is in reasonable agreement with this prediction. VL - 7 UR - http://stacks.iop.org/1748-0221/7/i=02/a=C02039 U1 - FP U2 - PDG U5 - 2d03c7ff17e2f23b170fab1a1905e230 ER - TY - JOUR T1 - Temporally resolved plasma composition measurements by collective Thomson scattering in TEXTOR (invited) JF - Review of Scientific Instruments Y1 - 2012 A1 - Stejner, M. A1 - Korsholm, S. B. A1 - Nielsen, S.K. A1 - Salewski, M. A1 - Bindslev, H. A1 - Leipold, F. A1 - Michelsen, P. K. A1 - Meo, F. A1 - Moseev, D. A1 - Burger, A. A1 - Kantor, M. A1 - M.R. de Baar KW - chemical analysis KW - chemical variables measurement KW - cyclotrons KW - plasma diagnostics AB - Fusion plasma composition measurements by collective Thomson scattering (CTS) were demonstrated in recent proof-of-principle measurements in TEXTOR [S. B. Korsholm et al., Phys. Rev. Lett. 106, 165004 (2011)10.1103/PhysRevLett.106.165004]. Such measurements rely on the ability to resolve and interpret ion cyclotron structure in CTS spectra. Here, we extend these techniques to enable temporally resolved plasma composition measurements by CTS in TEXTOR, and we discuss the prospect for such measurements with newly installed hardware upgrades for the CTS system on ASDEX Upgrade. PB - AIP VL - 83 UR - http://link.aip.org/link/?RSI/83/10E307/1 U1 - FP U2 - PDG U5 - 78246d5261b1f858736e615d5cbbf57d ER - TY - JOUR T1 - Overview of ASDEX Upgrade results JF - Nuclear Fusion Y1 - 2011 A1 - Kallenbach, A. A1 - Adamek, J. A1 - Aho-Mantila, L. A1 - Akaslompolo, S. A1 - Angioni, C. A1 - Atanasiu, C. V. A1 - Balden, M. A1 - Behler, K. A1 - Belonohy, E. A1 - Bergmann, A. A1 - Bernert, M. A1 - Bilato, R. A1 - Bobkov, V. A1 - Boom, J. A1 - Bottino, A. A1 - Braun, F. A1 - Brudgam, M. A1 - Buhler, A. A1 - Burckhart, A. A1 - Chankin, A. A1 - Classen, I.G.J. A1 - Conway, G. D. A1 - Coster, D. P. A1 - de Marne, P. A1 - D'Inca, R. A1 - Drube, R. A1 - Dux, R. A1 - Eich, T. A1 - Endstrasser, N. A1 - Engelhardt, K. A1 - Esposito, B. A1 - Fable, E. A1 - Fahrbach, H. U. A1 - Fattorini, L. A1 - Fischer, R. A1 - Flaws, A. A1 - Funfgelder, H. A1 - Fuchs, J. C. A1 - Gal, K. A1 - Munoz, M. G. A1 - Geiger, B. A1 - Adamov, M. G. A1 - Giannone, L. A1 - Giroud, C. A1 - Gorler, T. A1 - da Graca, S. A1 - Greuner, H. A1 - Gruber, O. A1 - Gude, A. A1 - Gunter, S. A1 - Haas, G. A1 - Hakola, A. H. A1 - Hangan, D. A1 - Happel, T. A1 - Hauff, T. A1 - Heinemann, B. A1 - Herrmann, A. A1 - Hicks, N. A1 - Hobirk, J. A1 - Hohnle, H. A1 - Holzl, M. A1 - Hopf, C. A1 - Horton, L. A1 - Huart, M. A1 - Igochine, V. A1 - Ionita, C. A1 - Janzer, A. A1 - Jenko, F. A1 - Kasemann, C. P. A1 - Kalvin, S. A1 - Kardaun, O. A1 - Kaufmann, M. A1 - Kirk, A. A1 - Klingshirn, H. J. A1 - Kocan, M. A1 - Kocsis, G. A1 - Kollotzek, H. A1 - Konz, C. A1 - Koslowski, R. A1 - Krieger, K. A1 - Kurki-Suonio, T. A1 - Kurzan, B. A1 - Lackner, K. A1 - Lang, P. T. A1 - Lauber, P. A1 - Laux, M. A1 - Leipold, F. A1 - Leuterer, F. A1 - Lohs, A. A1 - N C Luhmann Jr. A1 - Lunt, T. A1 - Lyssoivan, A. A1 - Maier, H. A1 - Maggi, C. A1 - Mank, K. A1 - Manso, M. E. A1 - Maraschek, M. A1 - Martin, P. A1 - Mayer, M. A1 - McCarthy, P. J. A1 - McDermott, R. A1 - Meister, H. A1 - Menchero, L. A1 - Meo, F. A1 - Merkel, P. A1 - Merkel, R. A1 - Mertens, V. A1 - Merz, F. A1 - Mlynek, A. A1 - Monaco, F. A1 - Muller, H. W. A1 - Munich, M. A1 - Murmann, H. A1 - Neu, G. A1 - Neu, R. A1 - Nold, B. A1 - Noterdaeme, J. M. A1 - Park, H. K. A1 - Pautasso, G. A1 - Pereverzev, G. A1 - Podoba, Y. A1 - Pompon, F. A1 - Poli, E. A1 - Polochiy, K. A1 - Potzel, S. A1 - Prechtl, M. A1 - Puschel, M. J. A1 - Putterich, T. A1 - Rathgeber, S. K. A1 - Raupp, G. A1 - Reich, M. A1 - Reiter, B. A1 - Ribeiro, T. A1 - Riedl, R. A1 - Rohde, V. A1 - Roth, J. A1 - Rott, M. A1 - Ryter, F. A1 - Sandmann, W. A1 - Santos, J. A1 - Sassenberg, K. A1 - Sauter, P. A1 - Scarabosio, A. A1 - Schall, G. A1 - Schmid, K. A1 - Schneider, P. A. A1 - Schneider, W. A1 - Schramm, G. A1 - Schrittwieser, R. A1 - Schweinzer, J. A1 - Scott, B. A1 - Sempf, M. A1 - Serra, F. A1 - Sertoli, M. A1 - Siccinio, M. A1 - Sigalov, A. A1 - Silva, A. A1 - Sips, A.C.C. A1 - Sommer, F. A1 - Stabler, A. A1 - Stober, J. A1 - Streibl, B. A1 - Strumberger, E. A1 - Sugiyama, K. A1 - Suttrop, W. A1 - Szepesi, T. A1 - Tardini, G. A1 - Tichmann, C. A1 - Told, D. A1 - Treutterer, W. A1 - Urso, L. A1 - Varela, P. A1 - Vincente, J. A1 - Vianello, N. A1 - Vierle, T. A1 - Viezzer, E. A1 - Vorpahl, C. A1 - Wagner, D. A1 - Weller, A. A1 - Wenninger, R. A1 - Wieland, B. A1 - Wigger, C. A1 - Willensdorfer, M. A1 - Wischmeier, M. A1 - Wolfrum, E. A1 - Wursching, E. A1 - Yadikin, D. A1 - Yu, Q. A1 - Zammuto, I. A1 - Zasche, D. A1 - Zehetbauer, T. A1 - Zhang, Y. A1 - Zilker, M. A1 - Zohm, H. KW - PHYSICS KW - REFLECTOMETRY KW - TOKAMAK AB - The ASDEX Upgrade programme is directed towards physics input to critical elements of the ITER design and the preparation of ITER operation, as well as addressing physics issues for a future DEMO design. After the finalization of the tungsten coating of the plasma facing components, the re-availability of all flywheel-generators allowed high-power operation with up to 20 MW heating power at I(p) up to 1.2 MA. Implementation of alternative ECRH schemes (140 GHz O2- and X3-mode) facilitated central heating above n(e) = 1.2 x 10(20) m(-3) and low q(95) operation at B(t) = 1.8 T. Central O2-mode heating was successfully used in high P/R discharges with 20 MW total heating power and divertor load control with nitrogen seeding. Improved energy confinement is obtained with nitrogen seeding both for type-I and type-III ELMy conditions. The main contributor is increased plasma temperature, no significant changes in the density profile have been observed. This behaviour may be explained by higher pedestal temperatures caused by ion dilution in combination with a pressure limited pedestal and hollow nitrogen profiles. Core particle transport simulations with gyrokinetic calculations have been benchmarked by dedicated discharges using variations of the ECRH deposition location. The reaction of normalized electron density gradients to variations of temperature gradients and the T(e)/T(i) ratio could be well reproduced. Doppler reflectometry studies at the L-H transition allowed the disentanglement of the interplay between the oscillatory geodesic acoustic modes, turbulent fluctuations and the mean equilibrium E x B flow in the edge negative E(r) well region just inside the separatrix. Improved pedestal diagnostics revealed also a refined picture of the pedestal transport in the fully developed H-mode type-I ELM cycle. Impurity ion transport turned out to be neoclassical in between ELMs. Electron and energy transport remain anomalous, but exhibit different recovery time scales after an ELM. After recovery of the pre-ELM profiles, strong fluctuations develop in the gradients of n(e) and T(e). The occurrence of the next ELM cannot be explained by the local current diffusion time scale, since this turns out to be too short. Fast ion losses induced by shear Alfven eigenmodes have been investigated by time-resolved energy and pitch angle measurements. This allowed the separation of the convective and diffusive loss mechanisms. VL - 51 SN - 0029-5515 IS - 9 N1 - ISI Document Delivery No.: 818DPTimes Cited: 1Cited Reference Count: 45SI U1 - FP U2 - PDG U5 - a193177a90d5b600862ca1e40bcc67af ER - TY - JOUR T1 - Comparison of measured and simulated fast ion velocity distributions in the TEXTOR tokamak JF - Plasma Physics and Controlled Fusion Y1 - 2011 A1 - Moseev, D. A1 - Meo, F. A1 - Korsholm, S. B. A1 - Koskela, T. A1 - Albergante, M. A1 - Asunta, O. A1 - Bindslev, H. A1 - Burger, A. A1 - Furtula, V. A1 - Kantor, M. Y. A1 - Leipold, F. A1 - Michelsen, P. K. A1 - Nielsen, S.K. A1 - Salewski, M. A1 - Schmitz, O. A1 - Stejner, M. A1 - Westerhof, E. KW - collective Thomson scattering KW - JET KW - PLASMAS KW - TRANSPORT AB -Here we demonstrate a comprehensive comparison of collective Thomson scattering (CTS) measurements with steady-state Monte Carlo simulations performed with the ASCOT and VENUS codes. The measurements were taken at a location on the magnetic axis as well as at an off-axis location, using two projection directions at each location. The simulations agree with the measurements on-axis, but for the off-axis geometries discrepancies are observed for both projection directions. For the near perpendicular projection direction with respect to the magnetic field, the discrepancies between measurement and simulations can be explained by uncertainty in plasma parameters. However, the discrepancies between measurement and simulations for the more parallel projection direction cannot be explained solely by uncertainties in plasma parameters. Here anomalous fast ion transport is a possible explanation for the discrepancy.

VL - 53 SN - 0741-3335 IS - 10 N1 - ISI Document Delivery No.: 823VVTimes Cited: 0Cited Reference Count: 40 U1 -FP

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U5 - 0c10e954e14bb5fee706a258ed42bf0d ER - TY - JOUR T1 - Dynamics of fast ions during sawtooth oscillations in the TEXTOR tokamak measured by collective Thomson scattering JF - Nuclear Fusion Y1 - 2011 A1 - Nielsen, S.K. A1 - Salewski, M. A1 - Bindslev, H. A1 - Burger, A. A1 - Furtula, V. A1 - Kantor, M. A1 - Korsholm, S. B. A1 - Koslowski, H. R. A1 - Kramer-Flecken, A. A1 - Leipold, F. A1 - Meo, F. A1 - Michelsen, P. K. A1 - Moseev, D. A1 - Oosterbeek, J. W. A1 - Stejner, M. A1 - Westerhof, E. KW - BEHAVIOR KW - CRASHES KW - DISRUPTIONS KW - FLUCTUATIONS KW - FUSION PLASMAS KW - JET KW - REDISTRIBUTION KW - STABILIZATION KW - TEMPERATURE KW - WAVES AB -Experimental investigations of sawteeth interaction with fast ions measured by collective Thomson scattering on TEXTOR are presented. Time-resolved measurements of localized 1D fast-ion distribution functions allow us to study fast-ion dynamics during several sawtooth cycles. Sawtooth oscillations interact strongly with the fast-ion population in a wide range of plasma parameters. Part of the ion phase space density oscillates out of phase with the sawtooth oscillation during hydrogen neutral beam injection (NBI). These oscillations most likely originate from fast hydrogen ions with energies close to the full injection energy. At lower energies passing fast ions in the plasma centre are strongly redistributed at the time of sawtooth collapse but no redistribution of trapped fast ions is observed. The redistribution of fast ions from deuterium NBI in the plasma centre is found to vary throughout velocity space. The reduction is most pronounced for passing ions. We find no evidence of inverted sawteeth outside the sawtooth inversion surface in the fast-ion distribution function.

VL - 51 SN - 0029-5515 IS - 6 N1 - ISI Document Delivery No.: 766MWTimes Cited: 0Cited Reference Count: 39 U1 -FP

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U5 - 67db4fe34a6d341f7d3fa7d646132c7d ER - TY - JOUR T1 - Measurements of Intrinsic Ion Bernstein Waves in a Tokamak by Collective Thomson Scattering JF - Physical Review Letters Y1 - 2011 A1 - Korsholm, S. B. A1 - Stejner, M. A1 - Bindslev, H. A1 - Furtula, V. A1 - Leipold, F. A1 - Meo, F. A1 - Michelsen, P. K. A1 - Moseev, D. A1 - Nielsen, S.K. A1 - Salewski, M. A1 - de M. Baar A1 - Delabie, E. A1 - Kantor, M. A1 - Burger, A. KW - FLUCTUATIONS KW - MICROTOR TOKAMAK KW - PLASMA AB -In this Letter we report measurements of collective Thomson scattering (CTS) spectra with clear signatures of ion Bernstein waves and ion cyclotron motion in tokamak plasmas. The measured spectra are in accordance with theoretical predictions and show clear sensitivity to variation in the density ratio of the main ion species in the plasma. Measurements with this novel diagnostic demonstrate that CTS can be used as a fuel ion ratio diagnostic in burning fusion plasma devices.

VL - 106 SN - 0031-9007 UR - http://prl.aps.org/abstract/PRL/v106/i16/e165004 IS - 16 U1 -FP

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U5 - 174415faa0661f065e2d2ce73b082632 ER - TY - JOUR T1 - Collective Thomson scattering measurements with high frequency resolution at TEXTOR JF - Review of Scientific Instruments Y1 - 2010 A1 - Stejner, M. A1 - Nielsen, S.K. A1 - Korsholm, S. B. A1 - Salewski, M. A1 - Bindslev, H. A1 - Furtula, V. A1 - Leipold, F. A1 - Meo, F. A1 - Michelsen, P. K. A1 - Moseev, D. A1 - Burger, A. A1 - Kantor, M. A1 - de M. Baar AB - We discuss the development and first results of a receiver system for the collective Thomson scattering (CTS) diagnostic at TEXTOR with frequency resolution in the megahertz range or better. The improved frequency resolution expands the diagnostic range and utility of CTS measurements in general and is a prerequisite for measurements of ion Bernstein wave signatures in CTS spectra. The first results from the new acquisition system are shown to be consistent with theory and with simultaneous measurements by the standard receiver system. [doi:10.1063/1.3475540] VL - 81 SN - 0034-6748 UR -