Speaker
Mathias Hoppe
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.J603.pdf
Simulations of bremsstrahlung and synchrotron radiation from runaway
electrons
M. Hoppe, O. Embréus, P. Svensson, L. Unnerfelt, T. Fülöp
Department of Physics, Chalmers University of Technology, Göteborg 412 96, Sweden
The main method for diagnosing runaway electrons in tokamak experiments is to measure the
radiation they emit. Both the bremsstrahlung (BR) [1, 2] and synchrotron radiation (SR) [3, 4]
emission from runaways is strongly dependent on particle energy, pitch angle and position, and
thus provide valuable insight into runaway electron dynamics. In this contribution we present
recent developments of the Synchrotron-detecting Orbit Following Toolkit (SOFT) [5], which
has previously been used to study SR images and spectra [5, 6]. Specifically we present the
implementation of BR and the polarization of SR in SOFT, and analyze the effects of first-order
corrections to the guiding-center motion.
Due to the strong anisotropy of both BR and SR, the camera images from both types of
radiation depend strongly, and in a similar way, on the runaway pitch-angle and radial distribu-
tions [6]. The amount of emitted SR however increases with energy, while it decreases for BR,
thus causing different parts of the momentum-space distribution function to dominate emission
of each type, effectively allowing different parts of momentum-space to be analyzed.
Another technique suggested for acquiring sufficient data to unambiguously infer both the
dominant energy and pitch angle of the runaways is to measure the polarization components of
SR. We consider its usefulness as a diagnostic technique as well as its implementation in SOFT.
The high energy of runaway electrons is associated with large guiding-center drift orbits
which shift guiding-centers away from magnetic flux surfaces and hence modify spatial dis-
tribution of runaways. The high energy is however also associated with perturbations to the
particles’ gyro-motion, which will change the gyro-averaged angular distribution of radiation
emitted by runaways and which must also be considered in a consistent treatment. We estimate
the relative importance of these effects from a radiation-detection point-of-view and show that
they must both be included in a model based on first order guiding-center theory.
References
[1] Y. Peysson et al., Rev. Sci. Instrum. 70, 3987 (1999).
[2] C. Paz-Soldan et al., Phys. Rev. Lett. 118, 255002 (2017).
[3] K. H. Finken et al., Nucl. Fusion 30, 859 (1990).
[4] R. J. Zhou et al., Phys. Plasmas 21, 063302 (2014).
[5] M. Hoppe et al., Nucl. Fusion 58, 026032 (2018).
[6] M. Hoppe et al., Accepted for publication in Nucl. Fusion (2018).
