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- Fasoli, A., et al.
(författare)
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Chapter 5 : Physics of energetic ions
- 2007
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 47:6, s. S264-S284
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Forskningsöversikt (refereegranskat)abstract
- This chapter reviews the progress accomplished since the redaction of the first ITER Physics Basis (1999 Nucl. Fusion 39 2137-664) in the field of energetic ion physics and its possible impact on burning plasma regimes. New schemes to create energetic ions simulating the fusion-produced alphas are introduced, accessing experimental conditions of direct relevance for burning plasmas, in terms of the Alfvenic Mach number and of the normalised pressure gradient of the energetic ions, though orbit characteristics and size cannot always match those of ITER. Based on the experimental and theoretical knowledge of the effects of the toroidal magnetic field ripple on direct fast ion losses, ferritic inserts in ITER are expected to provide a significant reduction of ripple alpha losses in reversed shear configurations. The nonlinear fast ion interaction with kink and tearing modes is qualitatively understood, but quantitative predictions are missing, particularly for the stabilisation of sawteeth by fast particles that can trigger neoclassical tearing modes. A large database on the linear stability properties of the modes interacting with energetic ions, such as the Alfven eigenmode has been constructed. Comparisons between theoretical predictions and experimental measurements of mode structures and drive/damping rates approach a satisfactory degree of consistency, though systematic measurements and theory comparisons of damping and drive of intermediate and high mode numbers, the most relevant for ITER, still need to be performed. The nonlinear behaviour of Alfven eigenmodes close to marginal stability is well characterized theoretically and experimentally, which gives the opportunity to extract some information on the particle phase space distribution from the measured instability spectral features. Much less data exists for strongly unstable scenarios, characterised by nonlinear dynamical processes leading to energetic ion redistribution and losses, and identified in nonlinear numerical simulations of Alfven eigenmodes and energetic particle modes. Comparisons with theoretical and numerical analyses are needed to assess the potential implications of these regimes on burning plasma scenarios, including in the presence of a large number of modes simultaneously driven unstable by the fast ions.
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| 2. |
- Hedén, Martin, 1976, et al.
(författare)
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Thermal radiation from CN+ and La@CN
- 2005
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Ingår i: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 123
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Tidskriftsartikel (refereegranskat)abstract
- The radiative cooling of positively charged fullerene and endohedral fullerene fragments of C60, C70, C84, and La@C82 has been measured in a time-of-flight mass spectrometer. The radiative cooling is measured via its influence on the metastable decay. The emissivity extracted from the data is between 4×10–4 and 13×10–4. These values agree fairly well with the emissivity calculated from considering the low-energy tail of the surface plasmon. No major difference is found in the emission behavior of empty and endohedral fullerenes.
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| 3. |
- Lassesson, Andreas, 1976, et al.
(författare)
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A femtosecond laser study of the endoral fullerenes Li@C60 and La@C82
- 2005
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Ingår i: Eur. Phys. J. D. - : Springer Science and Business Media LLC. - 1434-6060. ; 34, s. 205-209
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Tidskriftsartikel (refereegranskat)abstract
- The endohedral fullerenes La@C82 and Li@C60 have been studied in the gas phase with femtosecond laser excitation. The two molecules show qualitatively the same behaviour with respect to ion yield vs. pulse energy, but markedly different fragmentation patterns, with La@C82 fragmenting via the shrink-wrap mechanism and Li@C60 predominantly losing the metal atom in the first fragmentation step. The ion yields and electron energy distributions of La@C82 agree well with a recently developed model for fs laser ionisation of C60.
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| 4. |
- Lonnroth, J. S., et al.
(författare)
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Effects of ripple-induced ion thermal transport on H-mode plasma performance
- 2007
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 49:3, s. 273-295
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Tidskriftsartikel (refereegranskat)abstract
- A recent series of dimensionless pedestal identity experiments at JET and JT-60U failed to produce a match in the dimensional pedestal parameters and edge-localized mode (ELM) frequency despite a good match in the main dimensionless plasma parameters. This paper describes the progress made in understanding these experimental results. First, it is investigated whether differences in the magnetohydrodynamic stability of the pedestal, including those potentially arising from the 10% difference in the aspect ratio between the two tokamaks, can explain the results. The potential effects of differences in plasma rotation between the two machines are also examined. Given the result that these mechanisms fail to explain the experimental observations and the fact that JT-60U features considerably stronger toroidal magnetic field ripple than JET, the bulk of the paper, however, discusses the effects of ripple losses. The analysis shows that ripple losses of thermal ions can affect H-mode plasma performance very sensitively. Orbit-following simulations indicate that losses due to diffusive transport give rise to a wide radial distribution of enhanced ion thermal transport, whereas non-diffusive losses have a very edge-localized distribution. In predictive transport simulations with an energy sink term in the continuity equation for the ion pressure representing non-diffusive losses, reduced performance as well as an increase in the ELM
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| 6. |
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| 7. |
- Popok, Vladimir, 1966, et al.
(författare)
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Electronic Properties of thin films sublimed from La@C82 and Li@C60
- 2008
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Ingår i: Nano. ; 3:3, s. 155-160
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Tidskriftsartikel (refereegranskat)abstract
- La@C82 and Li@C60 thin films obtained by sublimation in vacuum are studied using four-probe current-voltage measurements and atomic force microscopy. In situ electrical measurements show semiconducting behavior of both films with room-temperature resistivity of 21+-8 and 1230+-50 Ohm.cm for the La@C82 and Li@C60, respectively. A variable range hopping mechanism of conductance is suggested from the temperature dependences of resistance. The activation energies for electron transport are calculated for both metallofullerenes. Irreversible changes to the Li@C60 film structure increasing the film resistivity to values typical for C60 are found at elevated temperatures. The effect of exposure to ambient atmosphere on the conductance of the films is discussed.
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