| 1. |
- Askinazi, L. G., et al.
(author)
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Evolution of geodesic acoustic mode in ohmic H-mode in TUMAN-3M tokamak
- 2012
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In: Technical physics letters. - 1063-7850 .- 1090-6533. ; 38:3, s. 268-271
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Journal article (peer-reviewed)abstract
- The behavior of a geodesic acoustic mode (GAM) in the TUMAN-3M tokamak has been experimentally studied using the heavy-ion beam probing technique. Oscillations of the electric potential under the action of a GAM localized at the plasma periphery have been detected. The GAM was observed in the regime of low confinement (L-mode) with low plasma density (similar to 0.8 x 10(19) m(-3)) and disappeared upon the transition to a high confinement regime (H-mode). The possible role of GAM as a precursor of the improved confinement (LH-transition) is discussed.
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| 2. |
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| 3. |
- Askinazi, L. G., et al.
(author)
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Plasma potential evolution in various operational modes in the TUMAN-3M tokamak
- 2007
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In: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts. - 9781622763344 ; , s. 2010-2013
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Conference paper (peer-reviewed)abstract
- In a scenario with Counter-NBI it was found using HIBP that, due to the NBI effect (most probably, orbit loss with some heating and momentum impact), core plasma potential plasma gradually became more negative (for ∼200V). Strong positive perturbation of the core plasma potential was registered by the HIBP during the burst of peripheral MHDs with low m, n. If such a burst takes place in the H-mode (both ohmic and counter-NBI heated), the positive potential perturbation leads to H-mode termination. The most probable mechanism of the positive field build-up during MHD burst is though to be a loss of fast electrons along partly disturbed magnetic field lines near the island's separatrix [3,4]. This mechanism is similar to the ergodic divertor's action on the TEXTOR [6], where radial electric field modification by the electron loses was also discussed. A quantitative analysis of the subject may be found in [7]. Similar mechanism may be responsible for a positive perturbation of central plasma potential registered in the sawtooth crashes. The GAM with δφ/φ∼0.3 and δφ/φ≫δn/n∼0.05 where observed with HIBP in a core region of the TUMAN-3M r/a∼0.33 in the current ramp phase. Further studies are needed to reveal a possible connection between the GAM evolution and plasma confinement in the TUMAN-3M.
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| 4. |
- Askinazi, L. G., et al.
(author)
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Radial electric field evolution in various operational modes in the TUMAN-3M tokamak
- 2008
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 123, s. 012010-
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Journal article (peer-reviewed)abstract
- Radial electric field evolution has been studied on the TUAMN-3M tokamak in different modes of operation: ohmic and NBI heating, L- and H-modes, with and without strong MHD activity. Peripheral radial electric field was measured using Langmuire probes, which were inserted up to 2cm inside LCFS, while core plasma potential evolution was measured using HIBP diagnostic. It was found, that in presence of strong MHD activity radial electric field in a vicinity of the island changed sign from negative to positive and could reach up to 4kV/m. Central plasma potential exhibited a positive perturbation of ∼700V during the MHD burst. This positive radial electric field might lead to H-mode termination, both in ohmic and NBI heating cases. Possible mechanism of the positive Er generation, namely the electron losses along ergodized magnetic field lines in the presence of MHD-island, is discussed. The same mechanism might be responsible for the positive potential spikes during a saw-tooth crash, also observed using HIBP. Another phenomenon observed using HIBP was quasi-coherent potential oscillations with the frequency close to one of the GAM. Possible location of these oscillations in the core region r/a ∼ 0.33 is discussed.
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| 5. |
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| 6. |
- Severo, J. H. F., et al.
(author)
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Error analysis in the electron temperature measurements in TCABR
- 2012
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 370:1, s. 012045-
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Journal article (peer-reviewed)abstract
- An analytical method is proposed to evaluate the experimental uncertainty in the electron temperature measurements in the TCABR tokamak. Solving the integral equation resulting from the convolution of two functions, one representing, the scattered light and the other the spectral apparatus function, i.e., the polychromator, an analytical expression for the electron temperature is obtained, from which the uncertainty in the measured value is readily evaluated. The results show that the major contribution to the error comes from the noise in the signal; the uncertainties in the filters parameters do not contribute significantly to the total error.
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| 7. |
- Severo, J. H. F., et al.
(author)
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Magnetic islands and plasma rotation in the Tokamak Chauffage Alfven Bresilien tokamak
- 2004
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 11:2, s. 846-848
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Journal article (peer-reviewed)abstract
- Collisional plasma rotation in the Tokamak Chauffage Alfven Bresilien (TCABR) tokamak [J. H. F. Severo, I. C. Nascimento, V. S. Tsypin, and R. M. O. Galvao, Nucl. Fusion 43, 1047 (2003)] has been experimentally studied. It was found that the measured plasma poloidal rotation velocity agrees within error limits with neoclassical theoretical predictions, and toroidal velocity with experimental results obtained in analogous tokamaks, almost everywhere along the minor radius r, except for measurements at r/asimilar or equal to0.56 and r/asimilar or equal to0.89 (the minor radius of TCABR tokamak a=18 cm). For the first point, the measured plasma rotation velocities are higher than the velocity of the background plasma, respectively similar to30% and similar to10% for the poloidal and toroidal rotation velocities. Using a set of 22 Mirnov coils displaced poloidally, magnetic field perturbations were measured in shots adjusted to reproduce the ones of the previous plasma rotation measurements, and the results confirm that in the region r/asimilar or equal to0.89 the plasma rotates together with the magnetic island (3,1).
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| 8. |
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| 9. |
- Van Oost, G., et al.
(author)
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Turbulent transport reduction by E x B velocity shear during edge plasma biasing : recent experimental results
- 2003
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In: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 45:5, s. 621-643
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Journal article (peer-reviewed)abstract
- Experiments in the tokamaks TEXTOR, CASTOR, T-10 and ISTTOK, as well as in the reversed field pinch RFX have provided new and complementary evidence on the physics of the universal mechanism of E x B velocity shear stabilization of turbulence, concomitant transport barrier formation and radial conductivity by using various edge biasing techniques. In TEXTOR the causality between transport reduction and induced electric fields in the edge has been for the first time clearly demonstrated. The high electric field gradients have been identified as the cause for the quenching of turbulent cells. A quantitative analysis of the measured transport reduction is in good agreement with theoretical predictions. The scaling of plasma turbulence suppression with velocity shear has been established, revealing the density-potential cross-phase as a key element. Reduction in poloidal electric field, temperature, and density fluctuations across the shear layer lead to a reduction of the anomalous conducted and convected heat fluxes resulting in an energy transport barrier that is measured directly. In CASTOR the biasing electrode is placed at the separatrix in a non-intrusive configuration which has demonstrated strongly sheared electric fields and consequent improvement of the global particle confinement, as predicted by theory. The impact of sheared E x B flow on edge turbulent structures has been measured directly using a comprehensive set of electrostatic probe arrays as well as emissive probes. Measurements with a full poloidal Langmuir probe array have revealed quasi-coherent electrostatic waves in the SOL with a dominant mode number equal to the edge safety factor. In T-10 edge biasing is clearly improving the global performance of ECR heated discharges. Reflectometry and heavy ion beam probe measurements show the existence of a narrow plasma layer with strong suppression of turbulence. On ISTTOK, the influence of alternating positive and negative electrode and (non-intrusive) limiter biasing has been compared. Electrode biasing is found to be more efficient in modifying the radial electric field E, and confinement, limiter biasing acting mainly on the SOL. In the RFX reversed field pinch it has been demonstrated that also in RFPs biasing can increase the local E x B velocity shear in the edge region, and hence substantially reduce the local turbulence driven particle flux mainly due to a change in the relative phase between potential and density fluctuations.
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| 10. |
- Iiyoshi, A., et al.
(author)
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Muon catalyzed fusion, present and future
- 2019
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In: Proceedings of the international conference on advances and applications in plasma physics (aapp 2019). - : American Institute of Physics (AIP). - 9780735419261
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Conference paper (peer-reviewed)abstract
- The novel proposal of the Muon Catalyzed Fusion (MCF) concept is brought to light employing recent results on its relevant cross sections. In 1993, Kino et al. proposed an innovative scheme of MCF, employing non-adiabatic calculations of muonic atom-nucleus collision in the energy range from 10-3 eV to 100 eV, whereby the fusion in flight along with the formation of muonic molecular resonances was revisited [1]. In 1994, Froelich independently calculated the cross section up to 2 keV, and found the behavior of like resonance [2]. In 1996, Kino et al. examined these resonances, and concluded that the resonances were not suitable for MCF [3]. As a result, the research has been continued to examine the possibility of non-resonant In-flight Muon Catalyzed Fusion (IFMCF) calculating the muonic atom-nucleus collision cross-section with an improved precision within the optical model for nuclear reactions. The resultant fusion cross section was 2000 barns at 1.4 keV [4] which should be good enough to be used as a fast neutron source [5]. A research program has been initiated to confirm these results theoretically as well as experimentally. For the sake of the theoretical analysis, a few-body computer code has been put forward to handle the nuclear reactions for nucleon transfer. In this paper, an innovative compact reactor concept is proposed, based on IFMCF. In this concept, muons are injected to a gas target of D2 and T2, which is pressurized aerodynamically by the Mach shock wave using a supersonic stream generated in a Laval nozzle [6], [7]. It generates the output power of 28 MW with 1019 cm-3s-1 of fusions by supplying fresh muons of 1016 cm-3s-1 providing 1000 times of catalyzed cycle of reactions. To maintain Q values > 1, assuming 30% efficiency for thermal to electric conversion, the energy supply for muon production can be as low as 8 GeV/muons. One of the possible applications of muon catalyzed fusion is transmutation of long-lived fission products (LLFPs).
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