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The problem of explaining observed soft X-ray fluxes during solar flares,which invokes acceleration of large fraction of electrons, if the accelerationtakes places at the solar coronal loop-top, can potentially be solved bypostulating that flare at loop-top creates dispersive Alfven waves (DAWs) whichpropagate towards the foot-points. As DAWs move in progressively denser partsof the loop (due to gravitational stratification) the large fraction ofelectrons is no longer needed. Here we extend our previous results byconsidering $f ^{-1}$ frequency spectrum of DAWs and add ${\rm He^{++}}$ ionsusing fully kinetic particle-in-cell (PIC) simulations. We consider cases whentransverse density gradient is in the range ${ 4-40} c/\omega_{\rm { pe}}$ andDAW driving frequency is $0.3-0.6\omega_{\rm { cp}}$. We find that (i) Thefrequency spectrum case does not affect electron acceleration fraction in thelike-to-like cases, but few times larger percentage of ${\rm He^{++}}$ heatingis seen due to ion cyclotron resonance; (ii) In cases when counter propagatingDAWs collide multiple-times, much larger electron and ion accelerationfractions are found, but the process is intermittent in time. This is becauseintensive heating (temperature increase) makes the-above-thermal-fractionsmaller; Also more isotropic velocity distributions are seen; (iii) Developmentof kink oscillations occurs when DAWs collide; (iv) Scaling of the magneticfluctuations power spectrum steepening in the higher-density regions is seen,due to wave refraction. Our PIC runs produce much steeper slopes than theorginal spectrum, indicating that the electron-scale physics has a notableeffect of DAW spectrum evolution.

Particle acceleration by sub-proton cyclotron frequency spectrum of dispersive Alfven waves in inhomogeneous solar coronal plasmas