Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental and synthetic measurements of polarized synchrotron
  emission from runaway electrons in Alcator C-Mod   This paper presents the first experimental analysis of polarized synchrotron
emission from relativistic runaway electrons (REs) in a tokamak plasma.
Importantly, we show that the polarization information of synchrotron radiation
can be used to diagnose spatially-localized RE pitch angle distributions.
Synchrotron-producing REs were generated during low density, Ohmic, diverted
plasma discharges in the Alcator C-Mod tokamak. The ten-channel Motional Stark
Effect diagnostic was used to measure spatial profiles of the polarization
angle $\theta_{\mathrm{pol}}$ and the fraction $\mathrm{f}_{\mathrm{pol}}$ of
detected light that was linearly-polarized. Spatial transitions in
$\theta_{\mathrm{pol}}$ of 90$\deg$---from horizontal to vertical polarization
and vice versa---are observed in experimental data and are well-explained by
the gyro-motion of REs and high directionality of synchrotron radiation.
Polarized synchrotron emission is modeled with the synthetic diagnostic SOFT;
its output Green's (or detector response) functions reveal a critical RE pitch
angle at which $\theta_{\mathrm{pol}}$ flips by 90$\deg$ and
$\mathrm{f}_{\mathrm{pol}}$ is minimal. Using SOFT, we determine the dominant
RE pitch angle which reproduces measured $\theta_{\mathrm{pol}}$ and
$\mathrm{f}_{\mathrm{pol}}$ values. The spatiotemporal evolutions of
$\theta_{\mathrm{pol}}$ and $\mathrm{f}_{\mathrm{pol}}$ are explored in detail
for one C-Mod discharge. For channels viewing REs near the magnetic axis and
flux surfaces $q$ = 1 and 4/3, disagreements between synthetic and experimental
signals suggest that the sawtooth instability may be influencing RE dynamics.
Furthermore, other sources of pitch angle scattering, not considered in this
analysis, could help explain discrepancies between simulation and experiment.

33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
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The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex