What's the difference between stable and unstable plasma, and how do you know that the Covenant's is unstable? When it is formed into a ball to be fired as a torpedo, "unstable" plasma particles must come into contact with other "unstable" plasma particles... how come it doesn't explode inside the ship or just outside of it? And I assume that you think the Empire uses "stable" plasma, so why would stable plasma and unstable plasma explode, if unstable-unstable is supposed to explode? As far as I know, there is no scientific or sci-fi explanation for why charged particles should explode when they come into contact with other charged particles. Unless you have evidence to the contrary, and can explain it, then Covenant plasma would not explode.

Once again, if the slipspace portal is in between the Imperial ship and the Covenant ship, wouldn't it either be disrupted or disappear into slipspace?