If you equip the perk "killing an enemy with Arc Blade extends its duration", you can pretty much keep arc blade going forever as long as the enemies keep coming. The problem here is that I typically use "Razor's Edge" perk in conjunction with this, and so it is possible to shoot a wave of energy, have your super run out, then after your super has run out, the wave of energy kills an enemy and charges up your super again a bit. When this happens, you are stuck in this limbo arc blade state where it looks like you have your super, but you can't attack or do anything other than run around. The game seems to think your super already ended so you shouldn't be able to use it again, but the perk gives you some extra super energy so you go back into arc blade. I have died from this before because you have no way to attack. It doesn't seem like it should work that way, seems like a bug to me.