Numerical calculation of ion runaway distributions

Embréus, Ola; Newton, Sarah; Stahl, Adam; Hirvijoki, Eero; Fülöp, Tünde

doi:10.1063/1.4921661

Cited by 6 publications

(11 citation statements)

References 37 publications

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“…We solve the kinetic equation ( 2) numerically with the tool CODION (COllisional Distribution of IONs) [38]. CODION was originally developed to study highly energetic ion runaway mechanisms [64] in fusion and astrophysical plasmas.…”

Section: Spatiotemporal Evolution Of the Alpha Particle Distributionmentioning

confidence: 99%

“…However, in the case of such modes observed during the quench or postdisruption, the source of the drive is less obvious. Former analytical work on runaway ions [37] was inconclusive and it was later deduced [38] that ion runaway formation even in reactor-sized tokamaks is unlikely at disruption time scales. Spontaneous ion acceleration caused by internal magnetic reconnection events in the MAST tokamak were observed [39].…”

Section: Introductionmentioning

confidence: 99%

“…In section 2 we model the evolution of the main plasma parameter profiles during the disruption using GO [10,49,50], which are also used to construct the magnetic equilibrium. In section 3 we describe the calculation of the spatiotemporal evolution of the alpha distribution function using the CODION tool [38], and we show that a substantial suprathermal alpha population exists in the current quench. In section 4 we describe the LIGKA model [51] used to identify the Alfvén spectrum and mode structures.…”

Section: Introductionmentioning

confidence: 99%

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Alpha particle driven Alfvénic instabilities in ITER post-disruption plasmas

et al. 2021

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Fusion-born alpha particles in ITER disruption simulations are investigated as a possible drive of Alfvénic instabilities. The ability of these waves to expel runaway electron (RE) seed particles is explored in the pursuit of a passive, inherent RE mitigation scenario. The spatiotemporal evolution of the alpha particle distribution during the disruption is calculated using the linearized Fokker-Planck solver CODION coupled to a fluid disruption simulation. These simulations are done in the limit of no alpha particle transport during the thermal quench, which can be seen as a most pessimistic situation where there is also no RE seed transport. Under these assumptions, the radial anisotropy of the resulting alpha population provides free energy to drive Alfvénic modes during the quench phase of the disruption. We use the linear gyrokinetic magnetohydrodynamic code LIGKA to calculate the Alfvén spectrum and find that the equilibrium is capable of sustaining a wide range of modes. The self-consistent evolution of the mode amplitudes and the alpha distribution is calculated utilizing the wave-particle interaction tool HAGIS. Intermediate mode number (n = 7-15, 22-26) toroidal Alfvén eigenmodes are shown to saturate at an amplitude of up to δB/B ≈ 0.1% in the spatial regimes crucial for RE seed formation. We find that the mode amplitudes are predicted to be sufficiently large to permit the possibility of significant radial transport of REs.

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Section: Spatiotemporal Evolution Of the Alpha Particle Distributionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Alpha particle driven Alfvénic instabilities in ITER post-disruption plasmas

et al. 2021

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“…This means that the proton-ion collisions become inefficient, so the ions can be picked up by the flow of electrons and accelerated almost to the electron drift velocity (Gurevich 1961), v i ≈(Z − 1)v e /Z; these runaway ions start to appear when the electric field exceeds a critical field (Gurevich 1961;Embréus et al 2015) E ci , which is yet much smaller than the electron Dreicer field E De ; E ci ∼(m e /m p ) 1/3 E De . The result of this analytical consideration was fully confirmed by numerical simulations (Embréus et al 2015). Such "runaway" ions are routinely detected in laboratory experimens (Helander et al 2002;Fülöp & Landreman 2013;Zurro et al 2013;Eilerman et al 2015).…”

Section: Ion Trapsmentioning

confidence: 99%

Ion Traps at the Sun: Implications for Elemental Fractionation

Fleishman

Musset

Bommier

et al. 2018

ApJ

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Why the tenuous solar outer atmosphere, or corona, is much hotter than the underlying layers remains one of the greatest challenge for solar modeling. Detailed diagnostics of the coronal thermal structure come from extreme ultraviolet (EUV) emission. The EUV emission is produced by heavy ions in various ionization states and depends on the amount of these ions and on plasma temperature and density. Any nonuniformity of the elemental distribution in space or variability in time affects thermal diagnostics of the corona. Here we theoretically predict ionized chemical element concentrations in some areas of the solar atmosphere, where the electric current is directed upward. We then detect these areas observationally, by comparing the electric current density with the EUV brightness in an active region. We found a significant excess in EUV brightness in the areas with positive current density rather than negative. Therefore, we report the observational discovery of substantial concentrations of heavy ions in current-carrying magnetic flux tubes, which might have important implications for the elemental fractionation in the solar corona known as the first ionization potential (FIP) effect. We call such areas of heavy ion concentration the "ion traps." These traps hold enhanced ion levels until they are disrupted by a flare whether large or small.

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“…16 High energy hydrogen ions (40 À 80 Â T i ) sourced by a neutral beam into a deuterium RFP plasma obey the test particle runaway model with an electric field induced by a global reconnection event. 17 Recent computational work 18 demonstrates the importance of collisional diffusion of runaway ions by comparison of Fokker-Planck calculations with test particle equations; this mandates going beyond test particle theory for explanation of ion dynamics in the RFP.…”

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confidence: 99%

Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma

et al. 2016

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While reconnection-driven ion heating is common in laboratory and astrophysical plasmas, the underlying mechanisms for converting magnetic to kinetic energy remain not fully understood. Reversed field pinch discharges are often characterized by rapid ion heating during impulsive reconnection, generating an ion distribution with an enhanced bulk temperature, mainly perpendicular to magnetic field. In the Madison Symmetric Torus, a subset of discharges with the strongest reconnection events develop a very anisotropic, high energy tail parallel to magnetic field in addition to bulk perpendicular heating, which produces a fusion neutron flux orders of magnitude higher than that expected from a Maxwellian distribution. Here, we demonstrate that two factors in addition to a perpendicular bulk heating mechanism must be considered to explain this distribution. First, ion runaway can occur in the strong parallel-to-B electric field induced by a rapid equilibrium change triggered by reconnection-based relaxation; this effect is particularly strong on perpendicularly heated ions which experience a reduced frictional drag relative to bulk ions. Second, the confinement of ions varies dramatically as a function of velocity. Whereas thermal ions are governed by stochastic diffusion along tearing-altered field lines (and radial diffusion increases with parallel speed), sufficiently energetic ions are well confined, only weakly affected by a stochastic magnetic field. High energy ions traveling mainly in the direction of toroidal plasma current are nearly classically confined, while counter-propagating ions experience an intermediate confinement, greater than that of thermal ions but significantly less than classical expectations. The details of ion confinement tend to reinforce the asymmetric drive of the parallel electric field, resulting in a very asymmetric, anisotropic distribution.

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Numerical calculation of ion runaway distributions

Cited by 6 publications

References 37 publications

Alpha particle driven Alfvénic instabilities in ITER post-disruption plasmas

Alpha particle driven Alfvénic instabilities in ITER post-disruption plasmas

Ion Traps at the Sun: Implications for Elemental Fractionation

Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma

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