Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks
- General Atomics, San Diego, CA (United States)
- Oak Ridge Associated Univ., Oak Ridge, TN (United States)
- Max-Planck Inst. for Plasma Physics, Greifswald (Germany)
- Princeton Univ., NJ (United States)
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Univ. of California, San Diego, CA (United States)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Novel spatial, temporal, and energetically resolved measurements of bremsstrahlung hard-x-ray (HXR) emission from runaway electron (RE) populations in tokamaks reveal nonmonotonic RE distribution functions whose properties depend on the interplay of electric field acceleration with collisional and synchrotron damping. Measurements are consistent with theoretical predictions of momentum-space attractors that accumulate runaway electrons. RE distribution functions are measured to shift to a higher energy when the synchrotron force is reduced by decreasing the toroidal magnetic field strength. Increasing the collisional damping by increasing the electron density (at a fixed magnetic and electric field) reduces the energy of the nonmonotonic feature and reduces the HXR growth rate at all energies. Higher-energy HXR growth rates extrapolate to zero at the expected threshold electric field for RE sustainment, while low-energy REs are anomalously lost. The compilation ofHXR emission from different sight lines into the plasma yields energy and pitch-angle-resolved RE distributions and demonstrates increasing pitch-angle and radial gradients with energy.
- Research Organization:
- General Atomics, San Diego, CA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- FC02-04ER54698; FG02-07ER54917; AC05-00OR22725; FC02-99ER54512; SC0016268
- OSTI ID:
- 1374548
- Alternate ID(s):
- OSTI ID: 1365606
- Journal Information:
- Physical Review Letters, Vol. 118, Issue 25; ISSN 0031-9007
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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