An Explanation for the Different Locations of Electron and Ion Acceleration in Solar Flares

RHESSI observations of the 2002 July 23 solar flare have shown that hard X-rays and gamma rays are produced in different locations within the flare volume. The gamma-ray emission, which is a diagnostic of ion acceleration, appears to originate in the vicinity of large loops, while the hard X-ray emission, a diagnostic of electron acceleration, originates near shorter loops. The tendency for a stochastic acceleration model based on cascading MHD turbulence to favor ion acceleration in larger acceleration regions has been previously noted. Here we evaluate this effect quantitatively and show that such a model is consistent with the RHESSI observations.