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| 2. |
- Fülöp, Tünde, 1970, et al.
(författare)
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Magnetic field threshold for runaway generation in tokamak disruptions
- 2008
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Ingår i: 35th European Physical Society Conference on Plasma Physics, EPS 2008 Combined with the 10th International Workshop on Fast Ignition of Fusion Targets; Hersonissos, Crete; Greece; 9 June 2008 through 13 June 2008. - 9781622763351 ; 32:2, s. 1014-1017
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Konferensbidrag (refereegranskat)abstract
- Experimental observations on large tokamaks show that the number of runaway electrons produced in disruptions depends sensitively on the magnetic field strength. The presence of a whistler wave instability (WWI) excited by runaway electrons may be the reason for this observation since the linear growth rates of these waves are such that they are stable for high magnetic field (so the runaway beam can form) but unstable for low magnetic field. The quasi-linear diffusion process due to the WWI represents a very efficient pitch-angle scattering mechanism for runaways and consequently may stop runaway beam formation. In this work, the criterion for runaway suppression by WWI is compared with a criterion for substantial runaway production obtained by calculating how many runaway electrons can be produced before the induced toroidal electric field diffuses out of the plasma.
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| 3. |
- Fülöp, Tünde, 1970, et al.
(författare)
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Magnetic field threshold for runaway generation in tokamak disruptions
- 2009
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 16:2, s. 022502-
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Tidskriftsartikel (refereegranskat)abstract
- Experimental observations show that there is a magnetic field threshold for runaway electrongeneration in tokamak disruptions. In this work, two possible reasons for this threshold are studied.The first possible explanation for these observations is that the runaway beam excites whistler wavesthat scatter the electrons in velocity space prevents the beam from growing. The growth rates of themost unstable whistler waves are inversely proportional to the magnetic field strength. Taking intoaccount the collisional and convective damping of the waves it is possible to derive a magnetic fieldthreshold below which no runaways are expected. The second possible explanation is the magneticfield dependence of the criterion for substantial runaway production obtained by calculating howmany runaway electrons can be produced before the induced toroidal electric field diffuses out of theplasma. It is shown, that even in rapidly cooling plasmas, where hot-tail generation is expected togive rise to substantial runaway population, the whistler waves can stop the runaway formationbelow a certain magnetic field unless the postdisruption temperature is very low.
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| 4. |
- Guszejnov, David, et al.
(författare)
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Three-dimensional modeling of beam emission spectroscopy measurements in fusion plasmas
- 2012
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 83:11, s. 113501-
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Tidskriftsartikel (refereegranskat)abstract
- One of the main diagnostic tools for measuring electron density profiles and the characteristics of long wavelength turbulent wave structures in fusion plasmas is beam emission spectroscopy (BES). The increasing number of BES systems necessitated an accurate and comprehensive simulation of BES diagnostics, which in turn motivated the development of the Rate Equations for Neutral Alkali-beam TEchnique (RENATE) simulation code that is the topic of this paper. RENATE is a modular, fully three-dimensional code incorporating all key features of BES systems from the atomic physics to the observation, including an advanced modeling of the optics. Thus RENATE can be used both in the interpretation of measured signals and the development of new BES systems. The most important components of the code have been successfully benchmarked against other simulation codes. The primary results have been validated against experimental data from the KSTAR tokamak.
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| 5. |
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| 6. |
- Kómár, A, et al.
(författare)
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Electromagnetic waves destabilized by runaway electrons in near-critical electric fields
- 2013
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 20:1, s. 012117-
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Tidskriftsartikel (refereegranskat)abstract
- Runaway electron distributions are strongly anisotropic in velocity space. This anisotropy is a source of free energy that may destabilize electromagnetic waves through a resonant interaction between the waves and the energetic electrons. In this work, we investigate the high-frequency electromagnetic waves that are destabilized by runaway electron beams when the electric field is close to the critical field for runaway acceleration. Using a runaway electron distribution appropriate for the near-critical case, we calculate the linear instability growth rate of these waves and conclude that the obliquely propagating whistler waves are most unstable. We show that the frequencies, wave numbers, and propagation angles of the most unstable waves depend strongly on the magnetic field. Taking into account collisional and convective damping of the waves, we determine the number density of runaways that is required to destabilize the waves and show its parametric dependences.
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| 7. |
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| 8. |
- Kómár, A, et al.
(författare)
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Interaction of electromagnetic waves and suprathermal electrons in the near-critical electric field limit
- 2012
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 401:1
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Konferensbidrag (refereegranskat)abstract
- The velocity-space anisotropy of suprathermal electron distributions is a source of free energy that may destabilize plasma waves through a resonant interaction between the waves and the energetic electrons. In this work we use a suprathermal electron distribution appropriate for the case when the accelerating electric field is near-critical and we investigate the frequencies, wave numbers and propagation angles of the most unstable waves using a general dispersion relation. It is shown that if the electric field is sub-critical, the anisotropy is not enough to drive electromagnetic waves unstable, as the Landau damping of the waves overwhelms the drive through the anomalous Doppler resonance. In the case when the electric field is supercritical, two types of electromagnetic waves will be destabilized, the electron-whistler and the extraordinary electron wave. The number of electrons for destabilization of the latter is several orders of magnitude lower than for the electron-whistler wave. Consequently, the threshold for destabilization of the extraordinary electron wave is much lower.
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| 9. |
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| 10. |
- Papp, Gergely, 1985, et al.
(författare)
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Energetic electron transport in the presence of magnetic perturbations in magnetically confined plasmas
- 2015
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 81:3, s. 475810503-
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Tidskriftsartikel (refereegranskat)abstract
- The transport of energetic electrons is sensitive to magnetic perturbations. By using 3D numerical simulation of test particle drift orbits we show that the transport of untrapped electrons through an open region with magnetic perturbations cannot be described by a diffusive process. Based on our test particle simulations, we propose a model that leads to an exponential loss of particles.
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