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Recent observations from {\em RHESSI} have revealed that the number ofnon-thermal electrons in the coronal part of a flaring loop can exceed thenumber of electrons required to explain the hard X-ray-emitting footpoints ofthe same flaring loop. Such sources cannot, therefore, be interpreted on thebasis of the standard collisional transport model, in which electrons streamalong the loop while losing their energy through collisions with the ambientplasma; additional physical processes, to either trap or scatter the energeticelectrons, are required. Motivated by this and other observations that suggestthat high energy electrons are confined to the coronal region of the source, weconsider turbulent pitch angle scattering of fast electrons off low frequencymagnetic fluctuations as a confinement mechanism, modeled as a spatialdiffusion parallel to the mean magnetic field. In general, turbulent scatteringleads to a reduction of the collisional stopping distance of non-thermalelectrons along the loop and hence to an enhancement of the coronal HXR sourcerelative to the footpoints. The variation of source size $L$ with electronenergy $E$ becomes weaker than the quadratic behavior pertinent to collisionaltransport, with the slope of $L(E)$ depending directly on the mean free path$\lambda$ again pitch angle scattering. Comparing the predictions of the modelwith observations, we find that $\lambda \sim$$(10^8-10^9)$ cm for $\sim30$keV, less than the length of a typical flaring loop and smaller than, orcomparable to, the size of the electron acceleration region.

Turbulent pitch-angle scattering and diffusive transport of hard-X-ray producing electrons in flaring coronal loops