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Turbulent Transport of Fast Ions Due To Magnetic Flux Ropes

Creative Commons 'BY-NC-SA' version 4.0 license

The transport of fast ions in magnetic flux ropes in a laboratory plasma is studied. Strong perturbing flux ropes (δE ~175 V/m, δB ~7 G) are generated by secondary cathode-anode pair at the upgraded LArge Plasma Device (LAPD). A 500-1000 eV lithium ion test beam is passed through the turbulent region and recollected by a gridded collimated analyzer, revealing enhanced fast ion broadening attributable to flux rope perturbations. The broadening is observed to be well in excess of Coulomb scattering levels. Monte Carlo simulation is performed with model electrostatic and magnetic fields, revealing negligible spreading as a result of the magnetic perturbations. Modeled electrostatic perturbations are observed to broaden the beam by 3.0 mm2 at the closest recollection plane, increasing as the transit time squared further downstream. Transport attributed to electrostatic fluctuations has been shown to decrease with energy while magnetic transport does not. Enhanced fast ion transport observed during the flux rope off phase is presently unexplained.

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