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Title 468: Pair formation during disruptions
Name:Francesco Volpe () Affiliation:ORAU
Research Area:Disruptions Presentation time: Not requested
Co-Author(s): Alex James (UCSD)
Description: Provide first evidence of disruption-generated positrons.
Experimental Approach/Plan: Repeat #51 either with the scintillator array repositioned or with reverse Ip and BT to measure emission in the opposite direction. This will be a combination of backward emission from electrons (e-) and forward emission from positrons (e+). Because forward and backward emission of each specie are related to each other, it will be easy to recognize anomalies in the comparison with #51 (forward emission from e- and backward emission from e+) that might indicate the presence of disruption-generated positrons. Additionally it is proposed to discriminate between clockwise and counter-clockwise elliptical polarization in the oblique ECE. Finally, coincidence counters of the type used in accelerators or in positron emission tomography might be utilized.
Background: P. Helander predicted that, during disruptions, electron-positron pairs will form in collisions between runaway electrons and thermal ions [PRL 2003]. Not only the first experimental evidence of such phenomenon would be interesting from a basic science point of view, but it might also pave the way to innovative disruption mitigation applications by channelling part of the disruption energy into electron-positron pairs which will then annihilate in 511keV photons, relatively innocuous for the tokamak walls
Resource Requirements: --
Diagnostic Requirements: Essential: scintillator array. Desirable: oblique ECE, coincidence counters.
Analysis Requirements: --
Other Requirements: --