737 research outputs found
Convective transport suppression in the scrape-off layer using ion cyclotron resonance heating on the asdex upgrade tokamak
No full textTurbulence properties in the scrape-off layer (SOL) in the presence of ion cyclotron frequency heating (ICRH) are compared to instances where it is absent. The discharges are all in a high-confinement mode (H-mode) regime. During ICRH, the SOL plasma density increases whereas turbulence large-scale and convective structures are shown to be suppressed. The probability distribution function is thus recorded to be closer to a Gaussian, and a net decrease in the low-frequency density fluctuations is reflected in the power spectra. Consequently, the level of turbulent fluctuations decreases significantly. Turbulence suppression is also reported during edge localized modes (ELMs) where both the ELMs-induced transport and duration are strongly affected. The increase of neutrals by gas puffing did not alter this behavior. We deduce that ICRH can be used as to suppress convective transport and reduce the ELM's amplitude. © 2010 The American Physical Society.Antar GY, 2003, PHYS PLASMAS, V10, P419, DOI 10.1063-1.1536166; Antar GY, 2001, PHYS PLASMAS, V8, P1612, DOI 10.1063-1.1363663; Antar GY, 2001, PHYS REV LETT, V87, DOI 10.1103-PhysRevLett.87.065001; Antar GY, 2005, PHYS PLASMAS, V12, DOI 10.1063-1.1861894; Antar GY, 2008, PLASMA PHYS CONTR F, V50, DOI 10.1088-0741-3335-50-9-095012; Becoulet M, 2002, PHYS PLASMAS, V9, P2619, DOI 10.1063-1.1472501; BURES M, 1988, PLASMA PHYS CONTR F, V30, P149, DOI 10.1088-0741-3335-30-2-004; Colas L, 2007, PLASMA PHYS CONTR F, V49, pB35, DOI 10.1088-0741-3335-49-12B-S02; GROUP T, 1984, PLASMA PHYS CONTROLL, V26, P1141, DOI 10.1088-0741-3335-26-9-011; Gruber O, 2001, NUCL FUSION, V41, P1369, DOI 10.1088-0029-5515-41-10-306; HOFMANN JV, 1990, FUSION ENG DES, V12, P185, DOI 10.1016-0920-3796(90)90078-K; Krasheninnikov SI, 2001, PHYS LETT A, V283, P368, DOI 10.1016-S0375-9601(01)00252-3; LEHRMAN IS, 1990, PLASMA PHYS CONTR F, V32, P51, DOI 10.1088-0741-3335-32-1-005; Milligen BP, 2005, PHYS PLASMAS, V12; MORISAKI T, 1995, PLASMA PHYS CONTR F, V37, P787, DOI 10.1088-0741-3335-37-7-008; MYRA JR, 1994, PHYS PLASMAS, V1, P2890, DOI 10.1063-1.870529; NIEUWENHOVE RV, 1990, FUSION ENG DES, V12, P231; NOTERDAEME JM, 1998, P 17 IAEA C FUS EN I; NOTERDAEME JM, 1993, PLASMA PHYS CONTR F, V35, P1481, DOI 10.1088-0741-3335-35-11-001; SAMM U, 1987, PLASMA PHYS CONTR F, V29, P1321, DOI 10.1088-0741-3335-29-10A-313; TAMAI H, 1990, FUSION ENG DES, V12, P25, DOI 10.1016-0920-3796(90)90060-J; VANNIEUWENHOVE R, 1990, FUSION ENG DES, V12, P231, DOI 10.1016-0920-3796(90)90085-K35
ANNETTE Project: Contributing to The Nuclearization of Fusion
No full textThe ANNETTE Project (Advanced Networking for Nuclear Education and Training and Transfer of Expertise) is well underway, and one of its work packages addresses the design, development and implementation of nuclear fusion training. A systematic approach is used that leads to the development of new training courses, based on identified nuclear competences needs of the work force of (future) fusion reactors and on the current availability of suitable training courses. From interaction with stakeholders involved in the ITER design and construction or the JET D-T campaign, it became clear that the lack of nuclear awareness already has an impact on current projects. Through the collaboration between the European education networks in fission (ENEN) and fusion (FuseNet) in the ANNETTE project, this project is well positioned to support the development of nuclear competences for ongoing and future fusion projects. Thereby it will make a clear contribution to the realization of fusion energy
Down-the-barrel observations of a multi-phase quasar outflow at high redshift
No full textWe present ultraviolet to near infrared spectroscopic observations of the quasar SDSS J001514+184212 and its proximate molecular absorber at z = 2.631. The [O III ] emission line of the quasar is composed of a broad ( FWHM ∼ 1600 km s −1 ), spatially unresolved component, blueshifted by about 600 km s −1 from a narrow, spatially-resolved component ( FWHM ∼ 650 km s −1 ). The wide, blueshifted, unresolved component is consistent with the presence of outflowing gas in the nuclear region. The narrow component can be further decomposed into a blue and a red blob with a velocity width of several hundred km s −1 each, seen ∼5 pkpc on opposite spatial locations from the nuclear continuum emission, indicating outflows on galactic scales. The presence of ionised gas on kpc scales is also seen from a weak C IV emission component, detected in the trough of a saturated C IV absorption that removes the strong nuclear emission from the quasar. Towards the nuclear emission, we observe absorption lines from atomic species in various ionisation and excitation stages and confirm the presence of strong H 2 lines originally detected in the SDSS spectrum. The overall absorption profile is very wide, spread over ∼600 km s −1 , and it roughly matches the velocities of the narrow blue [O III ] blob. From a detailed investigation of the chemical and physical conditions in the absorbing gas, we infer densities of about n H ∼ 10 4 − 10 5 cm −3 in the cold ( T ∼ 100 K) H 2 -bearing gas, which we find to be located at ∼10 kpc distances from the central UV source. We conjecture that we are witnessing different manifestations of a same AGN-driven multi-phase outflow, where approaching gas is intercepted by the line of sight to the nucleus. We corroborate this picture by modelling the scattering of Ly- α photons from the central source through the outflowing gas, reproducing the peculiar Ly- α absorption-emission profile, with a damped Ly- α absorption in which red-peaked, spatially offset, and extended Ly- α emission is seen. Our observations open up a new way to investigate quasar outflows at high redshift and shed light on the complex issue of AGN feedback
Using interactive eye-tracking and fMRI to investigate joint attention in a developmental sample with and without autism spectrum disorder.
No full textIn: Noterdaeme M., Dziobek I. (Hrsg.); WTAS, Tagunsgband Wissenschaftliche Gesellschaft Autismus Spektrum, Frankfurt, 2015, p. 5
Influence of the plasma on ICRF antenna voltage limits
No full textAn ion cyclotron range of frequencies (ICRF) probe [F.W. Baity, G.C. Barber, V. Bobkov, R.H. Goulding, J.-M. Noterdaeme, D.W. Swain, in: 14th Topical Conference on Radiofrequency Power in Plasmas, Oxnard 2001, AIP Conference Proceedings 595, AIP, Melville, NY, 2001, p. 510] has been implemented to study voltage stand-off of the ICRF antennas on ASDEX Upgrade (AUG). The probe was operated at first in a test stand where features of high RF voltage operation in vacuum and plasma created by an ion source of the Hall type [Plasma Sources Sci. Technol. 8 (1999) R1] were studied. Vacuum arcs as well as ignition of high voltage glow discharge are candidate processes to explain voltage limits of the ICRF antennas. The setup on AUG was used to expose high RF voltages in real conditions of the tokamak scrape-off layer which are faced by the ICRF antennas. It is found that high voltage breakdown on the ICRF antenna is often correlated with ELM activity. The maximal RF voltage increased from shot to shot, i.e. the conditioning effect
is observed. For the good-conditioned ICRF probe it was shown experimentally that the voltage limit can be increased while the rectified current is suppressed at the same time
Development of an experimental facility for the study of microparticle initiated radio frequency vacuum breakdown
No full textAn ongoing objective in the ion cyclotron range of frequencies (ICRF) systems is the improvement of power coupling to the plasma. During the last decade, this goal has been mainly pursued through the study of the coupling resistance, either by optimizing the antenna layout or by tailoring the scrape-off layer profile with gas puffing. Another approach is to increase the voltage handling capability of the ICRF system, limited by breakdown in the launchers or in the transmission lines. This paper describes the design of the ICRF Breakdown EXperiment (IBEX), a device to investigate fundamental aspects of radio frequency arcs under ICRF-relevant conditions. IBEX can achieve a peak voltage of 48 kV at 54 MHz with a 5 kW input power
Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments
No full textIn this paper we validate the finite element code RAPLICASOL, which models radiofrequency wave propagation in edge plasmas near ICRF antennas, against calculations with the TOPICA code. We compare the output of both codes for the ASDEX Upgrade 2-strap antenna, and for a 4-strap WEST-like antenna. Although RAPLICASOL requires considerably fewer computational resources than TOPICA, we find that the predicted quantities of experimental interest (including reflection coefficients, coupling resistances, - and -matrix entries, optimal matching settings, and even radiofrequency electric fields) are in good agreement provided we are careful to use the same geometry in both codes
Nieuwe Maerlantproblemen /
No full textOverdruk uit: Tijdschrift voor Nederlandse Taal- en Letterkunde; 82(1966)2-3, p. 81-11
Polarization Issues with High Power Injection and Low Power Emission in Fusion Experiments
No full textAll tokamak experiments using ECCD require setting of the beam elliptical polarization for proper coupling to the plasma. This is done either in the matching optics unit (MOU) at the output of the gyrotron, or in a couple of miter bends of the transmission line. Similarly, oblique ECE receivers require selection of the correct elliptical polarization to provide localized measurements. For the TCV tokamak at the CRPP, gyrotron and oblique-ECE polarizers are characterized during either high- or low- power testing of equipment: for the gyrotrons the behaviour is determined at a single frequency, but for the oblique-ECE the broadband response is needed. These characteristics are included in the calibration database and used during subsequent analysis of the power coupling to, or from, the sources (gyrotron, plasma, or low power transmitting antenna). A more detailed characterization has been carried out (at low power) with the MOU for the EU, 170GHz, 2MW, gyrotron prototype for ITER. This paper discusses the methodology and results of these measurements, as well as a review of nearly a decade's worth of experimental data from the 6 gyrotron, 3MW, 82.6GHz TCV system. In particular, the consistency between the calibrations and the subsequent data from tokamak experiments is analysed.CRPPSP
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