Speaker
Diego del-Castillo-Negrete
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1063.pdf
Synchrotron radiation of relativistic runaway electrons
D. del-Castillo-Negrete, L. Carbajal
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37831-8071, USA
The understanding of runaway electrons (RE) in magnetically confined plasmas is key for the
success of the controlled fusion program. If not avoided or mitigated, high energy relativistic
RE can significantly damage the plasma facing components of ITER. The study of synchrotron
radiation (SR) of RE in these plasmas is important because it provides a limiting mechanism
for the maximum energy that RE can reach, and because it can be used as an experimental di-
agnostic to infer RE parameters including energy and pitch-angle distributions. Here we report
recent results on SR taking into account full-orbit effects and the details of the SR camera ge-
ometry. The results were obtained using the recently developed SR synthetic diagnostic [1] for
the Kinetic Orbit Runaway electrons Code (KORC) [2] that computes the full-orbit relativis-
tic dynamics in electric and magnetic fields including radiation damping and collisions. SR is
studied in axisymmetric fields and in 3-D magnetic configurations exhibiting magnetic islands
and stochasticity [3]. For passing particles in axisymmetric fields, neglecting orbit effects might
underestimate or overestimate the total radiation power depending on the direction of the radial
shift of the drift orbits. For trapped particles, the spatial distribution of synchrotron radiation
exhibits localized “hot" spots at the tips of the banana orbits. The spatial distribution of syn-
chrotron radiation in stochastic magnetic fields, obtained using the MHD code NIMROD, is
strongly influenced by the presence of magnetic islands. 3-D magnetic fields also introduce a
toroidal dependence on the SR spectra, and neglecting orbit effects underestimates the total ra-
diation power. In the presence of magnetic islands, the radiation damping of trapped particles is
larger that the radiation damping of passing particles. Results modeling synchrotron emission by
RE in DIII-D quiescent plasmas are also presented. The computation uses EFIT reconstructed
magnetic fields and RE energy distributions fitted to the experimental measurements. Quali-
tative agreement is observed between simulations and experiments for simplified pitch angle
distributions. However, it is noted that to achieve quantitative agreement it is necessary to use
pitch angle distributions that depart from simplified 2-D phase-space Fokker-Planck models.
References
[1] L. Carbajal and D. del-Castillo-Negrete, Plasma Phys. Control. Fusion, 59, 124001 (2017).
[2] L. Carbajal, D. del-Castillo-Negrete, D. Spong, S. Seal, and L. Baylor, Phys. Plasmas, 24, 042512 (2017).
[3] D. del-Castillo-Negrete, L. Carbajal, D. Spong, and V. Izzo, Accepted for publication Phys. Plasmas (2018).
