Results 1 - 10 of 3784
Results 1 - 10 of 3784. Search took: 0.026 seconds
|Sort by: date | relevance|
[en] Our study demonstrates a remarkable flexibility of advanced divertor configurations created with the remote poloidal field coils. The emphasis here is on the configurations with three poloidal field nulls in the divertor area. We are seeking the structures where all three nulls lie on the same separatrix, thereby creating two zones of a very strong flux expansion, as envisaged in the concept of Takase's cusp divertor. It turns out that the set of remote coils can produce a cusp divertor, with additional advantages of: (i) a large stand-off distance between the divertor and the coils and (ii) a thorough control that these coils exert over the fine features of the configuration. In reference to these additional favourable properties acquired by the cusp divertor, the resulting configuration could be called 'a super-cusp'. General geometrical features of the three-null configurations produced by remote coils are described. Furthermore, issues on the way to practical applications include the need for a more sophisticated control system and possible constraints related to excessively high currents in the divertor coils
[en] We measured iron emission from the National Spherical Tokamak Experiment. We focused our attention on several band pass regions of the Solar Dynamics Observatory's Atmospheric Imaging Assembly. We found that all significant iron emission in the 171, 193 and 211 Å band pass regions are accounted for by the CHIANTI atomic database, although some strong emission lines of carbon are present that may complicate interpretation of solar data if not taken into account. (paper)
[en] In this study, observations of divertor plasma detachment in tokamaks are reviewed. Plasma detachment is characterized in terms of transport and dissipation of power, momentum and particle flux along the open field lines from the midplane to the divertor. Asymmetries in detachment onset and other characteristics between the inboard and outboard divertor plasmas is found to be primarily driven by plasma x drifts. The effect of divertor plate geometry and magnetic configuration on divertor detachment is summarized. Control of divertor detachment has progressed with a development of a number of diagnostics to characterize the detached state in real-time. Finally the compatibility of detached divertor operation with high performance core plasmas is examined.
[en] Highlights: • All the SNUs procured by the European Union for JT-60SA were completed. • An exhaustive set of tests were performed on the main components and on the complete SNUs. • The tests demonstrated the capabilities of the SNU to comply with the JT-60SA requirements. • The SNUs were delivered to Japan in October 2016. - Abstract: The plasma in the tokamak JT-60SA is initiated mainly by operating the four Switching Network Units (SNUs) inserted in the four modules of the Central Solenoid. In the framework of the “Broader Approach” agreement, these four SNUs were procured by the European Union. This paper presents the final assembly of the SNU system and the main tests performed in the last years before shipping it to Japan. The experimental results demonstrated the capabilities of the SNUs to comply with the JT-60SA requirements, even with better performances.
[en] Alfvén waves can induce the ejection of fast ions in different forms in tokamaks. In order to develop predictive capabilities to anticipate the nature of fast ion transport, a methodology is proposed to differentiate the likelihood of energetic-particle-driven instabilities to produce frequency chirping or fixed-frequency oscillations. Furthermore, the proposed method employs numerically calculated eigenstructures and multiple resonance surfaces of a given mode in the presence of energetic ion drag and stochasticity (due to collisions and micro-turbulence). Toroidicity-induced, reversed-shear and beta-induced Alfvén-acoustic eigenmodes are used as examples. Waves measured in experiments are characterized, and compatibility is found between the proposed criterion predictions and the experimental observation or lack of observation of chirping behavior of Alfvénic modes in different tokamaks. It is found that the stochastic diffusion due to micro-turbulence can be the dominant energetic particle detuning mechanism near the resonances in many plasma experiments, and its strength is the key as to whether chirping solutions are likely to arise. We proposed a criterion that constitutes a useful predictive tool in assessing whether the nature of the transport for fast ion losses in fusion devices will be dominated by convective or diffusive processes.
[en] An improved theory for the neoclassical polarization drift of the collisionless single ion with the arbitrary time-varying radial electric field is presented. A guiding-center motion code is used to numerically study the neoclassical polarization drift of a collisionless single ion in a model tokamak geometry. The results from the improved theory are compared with the numerical results and they agree with each other very well. The improved theory can be used to study the neoclassical polarization drift due to the fast time-varying radial electric field.
[en] In advanced of long pulse operation and experiments, a pulsed 5 GHz LHCD (Lower Hybrid Current Drive) system as an initial stage is under development aiming at first commissioning during 2012 KSTAR plasma campaign. A 5 GHz LHCD system will be used for the long pulse operation and the advanced tokamak experiments in KSTAR in next operation phase. This paper presents the fabrication status and key technology of the front coupler of the LH launcher
[en] Experiments on the Pegasus ST are advancing the physics and technology basis of local helicity injection (LHI). LHI injects helicity with relatively intense electron current sources in the plasma edge. It creates high toroidal current, toroidally-averaged tokamak-like plasmas that have been efficiently transitioned to Ohmically driven tokamak plasmas. Tradeoffs between physics and engineering goals are tested with LHI systems on the low-field-side and the high-field-side of Pegasus, producing plasmas predominantly driven by non-solenoidal induction and DC helicity drive, respectively. An extensive LHI source development campaign comparing active arc sources, passive and gas-effused electrode sources lead to the selection of active arc sources for present and next-step LHI deployments. LHI plasmas with net toroidal current MA, eV, and m−3 are attained to date. A predictive 0D power-balance model describes experimental and partitions the active current drive sources. High-frequency MHD activity is found to be present during LHI current drive, in addition to modes previously found in NIMROD simulation and experiment. A new regime of reduced MHD activity was discovered where activity is suppressed, LHI CD efficiency improves, and long-pulse plasmas are sustained with . (paper)
[en] It is shown that the statistical and correlation properties of the local turbulent flux measured at different radial locations of the cold, weakly ionized plasmas inside the Santander Linear Plasma Machine [Castellanos et al., Plasma Phys. Control. Fusion 47, 2067 (2005)] are consistent with diffusive-like transport dynamics. This is in contrast to the dynamical behavior inferred from similar measurements taken in hotter, fully ionized tokamak and stellarator edge plasmas, in which long-term correlations and other features characteristic of complex, non-diffusive transport dynamics have been reported in the past. These results may shed some light on a recent controversy regarding the possible universality of the dynamics of turbulent transport in magnetized plasmas