Abstract
The dynamics of RE (runaway electrons) in fusion plasmas span a wide range of temporal scales, from the fast gyro-motion, ∼10−11 s, to the observational time scales, ∼10−2→1 s. To cope with this scale separation, RE are usually studied within the bounce-average or the guiding center approximations. Although these approximations have yielded valuable insights, a study with predictive capabilities of RE in fusion plasmas calls for the incorporation of full orbit effects in configuration space in the presence of three-dimensional magnetic fields. We present numerical results on this problem using the Kinetic Orbit Runaway electrons Code that follows relativistic electrons in general electric and magnetic fields under the full Lorentz force, collisions, and radiation losses. At relativistic energies, the main energy loss is due to radiation damping, which we incorporate using the Landau-Lifshitz formulation of the Abraham-Lorentz-Dirac force. The main focus is on full orbit effects on synchrotron radiation. It is shown that even in the absence of magnetic field stochasticty, neglecting orbit dynamics can introduce significant errors in the computation of the total radiated power and the synchrotron spectra. The statistics of collisionless (i.e., full orbit induced) pitch angle dispersion, and its key role played on synchrotron radiation, are studied in detail. Numerical results are also presented on the pitch angle dependence of the spatial confinement of RE and on full orbit effects on the competition of electric field acceleration and radiation damping. Finally, full orbit calculations are used to explore the limitations of gyro-averaging in the relativistic regime. To explore the practical impact of the results, DIII-D and ITER-like parameters are used in the simulations.
Highlights
The potential impact that runaway electrons (RE) can have to the safe operation of ITER is currently wellrecognized
The majority of previous works on RE have been based on bounce-averaged Fokker-Planck models determining the evolution of the RE distribution function in a reduced 2-D phase space, e.g., pjj and p?
In this paper we have presented numerical results on full orbit effects on the dynamics or RE in magnetically confined fusion plasmas in toroidal geometry
Summary
The potential impact that runaway electrons (RE) can have to the safe operation of ITER is currently wellrecognized. The level of description is based on bounce-average approximations in the large aspectratio limit that eliminate all the spatial degrees of freedom and follow the individual dynamics of electrons in a 2-D momentum space.. The level of description is provided by models based on the guiding center approximation that eliminates the gyro-motion and follows the spatial degrees of freedom of the guiding center along with the parallel momentum, e.g., Refs. The most detailed description, which is the one adopted in the present paper, follows RE orbits in fully 3-D electric and magnetic fields using the exact relativistic Lorentz force, that is, the individual electron dynamics are evolved in a 6-D phase space. The main question we address is what is the impact of the full orbit effects, in general, and the spatial magnetic field information, in particular, on synchrotron radiation of RE in the highly relativistic regime.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
