Are you trying to make actual sparks here, or something that's you're calling a spark :X
Last time i saw sparks was from a buzzsaw cutting into some metal, and it looked a lot more like this.

I'd say the best thing to do is to go grab a few refences for the kind of sparks you want.
(i'll note i cheated on the above, using the 2 pixel diagonal brush, so it's a relatively quick effect to create, allowing me to recommend many frames of animation

)