Title: Measurements of runaway electron synchrotron spectra at high magnetic fields in Alcator C-Mod

Abstract

In the Alcator C-Mod tokamak, runaway electron (RE) experiments have been performed during low density, flattop plasma discharges at three magnetic fields: 2.7, 5.4, and 7.8 T, the last being the highest field to-date at which REs have been generated and measured in a tokamak. Time-evolving synchrotron radiation spectra were measured in the visible wavelength range (λ ≈ 300-1000 nm) by two absolutelycalibrated spectrometers viewing co- and counter-plasma current directions. In this paper, a test particle model is implemented to predict momentum-space and density evolutions of REs on the magnetic axis and q = 1, 3/2, and 2 surfaces. Drift orbits and subsequent loss of confinement are also incorporated into the evolution. These spatiotemporal results are input into the new synthetic diagnostic SOFT [M. Hoppe, et al., Nucl. Fusion 58(2), 026032 (2018)] which reproduces experimentally-measured spectra. For these discharges, it is inferred that synchrotron radiation dominates collisional friction as a power loss mechanism and that RE energies decrease as magnetic field is increased. Additionally, the threshold electric field for RE generation, as determined by hard X-ray and photo-neutron measurements, is compared to current theoretical predictions.

Authors:

Tinguely, Roy Alexander; Granetz, Robert; Hoppe, Mathias; Embreus, Ola

Publication Date:

2018-09-19

DOE Contract Number:  

FC02-99ER54512

Research Org.:

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY

OSTI Identifier:

1878737

DOI:

https://doi.org/10.7910/DVN/2ARZ0G