In this Letter we investigate factors that influence the effective critical electric field for runaway-electron generation in plasmas. We present numerical solutions of kinetic equation and discuss implications threshold field. show necessary significant formation often is higher than previously calculated due to both (1) extremely strong dependence primary on temperature (2) synchrotron radiation losses. also address context a transition from runaway growth decay. find agreement with recent...

Abstract In a recent experiment in the FT-2 tokamak, intermittencies GAM and turbulence intensities throughout 13 ms were observed while changes density temperature profiles are insignificant. The intensity of fluctuations measured by two reflectometers recorded 21% suppression during period radial region r/a = 0.4 to 0.8. this paper, several linear simulations one global non-linear simulation using gyrokinetic code GENE covering ρ tor from 0.17 0.83 carried out. Linear out find dominant...

The effects of kinetic whistler-wave instabilities on the runaway-electron (RE) avalanche is investigated. With parameters from DIII-D experiments, we show that RE scattering excited whistler waves can explain several poorly understood experimental results seen in a variety tokamaks. We find an increase growth rate and threshold electric field, bringing present model much closer to observations than previous results. excitation resonant electrons are calculated self-consistently using...

Runaway electrons are generated in a magnetized plasma when the parallel electric field exceeds critical value. For such with energies typically reaching tens of MeV, Abraham–Lorentz–Dirac (ALD) radiation force, reaction to synchrotron emission, is significant and can be dominant process limiting electron acceleration. The effect ALD force on runaway dynamics homogeneous investigated using relativistic finite-difference Fokker–Planck codes LUKE (Decker Peysson 2004 Report EUR-CEA-FC-1736,...

Abstract Mitigating edge localized modes (ELMs) with resonant magnetic perturbations (RMPs) can increase energetic particle losses and resulting wall loads, which have previously been studied in the vacuum approximation. This paper presents recent results of fusion alpha NBI ion ITER baseline scenario modelled Monte Carlo orbit following code ASCOT a realistic field including effect plasma response. The response was found to reduce but losses, up 4.2% injected power being lost. Additionally,...

Abstract Magnetohydrodynamic turbulence and magnetic reconnection are ubiquitous in astrophysical environments. In most situations these processes do not occur isolation but interact with each other. This renders a comprehensive theory of highly challenging. Here we propose magnetohydrodynamic driven at large scale that self-consistently accounts for the mutual interplay occurring smaller scales. Magnetic produces plasmoids (flux ropes) grow from turbulence-generated noise eventually disrupt...

We describe a density-, momentum-, and energy-conserving discretization of the nonlinear Landau collision integral. The method is suitable for both finite-element discontinuous Galerkin methods does not require structured meshes. conservation laws are proven algebraically demonstrated numerically an axially symmetric relaxation problem using implementation.

Runaway electrons, which are generated in a plasma where the induced electric field exceeds certain critical value, can reach very high energies MeV range. For such energetic radiative losses will contribute significantly to momentum space dynamics. Under conditions, due losses, non-monotonic feature - "bump" form runaway electron tail, creating potential for bump-on-tail-type instabilities arise. Here we study conditions existence of bump. We derive an analytical threshold condition bump...

We present a novel framework for addressing the nonlinear Landau collision integral in terms of finite element and other subspace projection methods. employ underlying metriplectic structure and, using Galerkin discretization velocity space, we transform infinite-dimensional system into finite-dimensional, time-continuous system. Temporal is accomplished concept discrete gradients. The conservation energy, momentum, particle densities, as well production entropy demonstrated algebraically...

We present a novel implementation of Monte Carlo particle-following code for solving the distribution function minority species in fusion plasmas, called ASCOT5, and verify it using theoretical results neoclassical transport. The has been developed from ground up with an OpenMP-MPI hybrid paradigm to take full advantage current next generation many-core CPUs multithreading SIMD operations. Up 6-fold increase performance is demonstrated compared previous version which only utilizes MPI....

A Monte Carlo method for the collisional guiding-center Fokker-Planck kinetic equation is derived in five-dimensional phase space, where effects of magnetic drifts due to background field nonuniformity are included. It shown that, limit a homogeneous field, our collision operator reduces Coulomb previously by Xu and Rosenbluth [Phys. Fluids B 3, 627 (1991)]. Applications present work will focus on transport energetic ions complex nonuniform magnetized plasmas large mean-free-path...

Disruption-generated runaway electrons (RE) present an outstanding issue for ITER. The predictive computational studies of RE generation rely on orbit-averaged computations and, as such, they lack the effects from magnetic field stochasticity. Since stochasticity is naturally in post-disruption plasma, and externally induced stochastization offers a prominent mechanism to mitigate avalanche, we advection–diffusion model that can be used couple orbit-following code tool order capture...

In this paper we show that the kinetic instabilities associated with runaway electron beams play an essential role for production of high-level non-thermal electron–cyclotron-emission (ECE) radiation. Most ECE comes from electrons in low-energy regime large pitch angle, which are strongly scattered by excited whistler waves. The power is obtained using a synthetic diagnostic model based on reciprocity method. distribution function calculated simulation including wave and quasilinear...

The fusion alpha and beam ion with steady-state power loads in all four main operating scenarios of ITER have been evaluated by the ASCOT code. For this purpose, high-fidelity magnetic backgrounds were reconstructed, taking into account even internal structure ferritic inserts tritium breeding modules (TBM). ions found to be almost perfectly confined scenarios, only so-called hybrid scenario featured reaching 0.5 MW due its more triangular plasma. TBMs not jeopardize confinement, nor cause...

The level and distribution of the wall power flux energetic ions in ITER have to be known accurately order ensure integrity first wall. Until now, most quantitative estimates been based on assumption that fast ion transport is dictated by neoclassical effects only. However, ITER, likely affected various MHD probably also microturbulence. We now upgraded our orbit-following Monte Carlo code ASCOT so it has simple, theory-based models for tearing mode (NTM)-type islands as well turbulent...

This paper contributes new insights into discretizing Coulomb collisions in kinetic plasma models. Building on the previous works [Carrillo et al. J. Comp. Phys. X 7:100066 (2020), Hirvijoki and Burby Plasmas 27(8):082307 (2020)], I propose deterministic discrete-time energy- positivity-preserving, entropy-dissipating marker-particle schemes for standard Landau collision operator electrostatic gyrokinetic operator. In case of operator, scheme preserves also momentum. The improvements,...

M. Kruskal showed that each continuous-time nearly periodic dynamical system admits a formal U(1)-symmetry, generated by the so-called roto-rate. When is also Hamiltonian, Noether's theorem implies existence of corresponding adiabatic invariant. We develop discrete-time analog Kruskal's theory. Nearly maps are defined as parameter-dependent diffeomorphisms limit to rotations along U(1)-action. limiting rotation non-resonant, these admit U(1)-symmetries all orders in perturbation For...

In this paper, we present the guiding-center transformation of radiation-reaction force a classical point charge traveling in nonuniform magnetic field. The is valid as long gyroradius charged particles much smaller than field nonuniformity length scale, so that Lie-transform method applicable. Elimination gyromotion time scale from obtained with Poisson bracket formalism originally introduced by [A. J. Brizard, Phys. Plasmas 11 4429 (2004)], where it was used to eliminate fast Fokker-Planck...

The magnetic perturbations due to in-vessel coils, foreseen mitigate edge-localized modes (ELMs) in ITER, could also compromise the confinement of energetic ions. We simulate losses fusion alpha particles and neutral beam injection-generated fast ions ITER under influence 3D caused by toroidal field ferritic inserts, test blanket modules ELM control coils (ECCs) with ASCOT code. ECCs are found stochastize deep inside pedestal 15 MA inductive reference operating scenario. Such a is...

We present the first results of 3D simulations global 13 C transport in ASDEX Upgrade (AUG) indicating that deposition profile exhibits toroidal asymmetry main chamber. In 2007, migration carbon AUG was studied with a methane ( CH 4 ) injection experiment (A. Hakola et al and Team 2010 Plasma Phys. Control. Fusion 52 065006 ). The total amount deposited estimated by assuming toroidally symmetric deposition. Remarkably, number atoms observed to be less than 10% injected atoms. has been...

The Landau collision integral is an accurate model for the small-angle dominated Coulomb collisions in fusion plasmas. We investigate a high order accurate, fully conservative, finite element discretization of nonlinear multispecies with adaptive mesh refinement using PETSc library (ŭlwww.mcs.anl.gov/petsc). develop algorithms and techniques to efficiently utilize emerging architectures approach that minimizes memory usage movement suitable vector processing. vectorized Intel AVX-512...