Thats kind of arcanes trope is it has to manage its mana. You are using the right talents, at around lvl 54 you will get using barrage gives you about 6% of your max mana back (1.5% per arcane charge). This will make your aoe pretty self sustaining. For single target fights you are either burning mana or conserving mana and you rotate through that during the fight.
When arcane power or rune of power+ magi are up you burn mana during them and then conserve. Burning mana is just spamming arcane blast and if you get clear casting using it. At the start of the fight use magi then arcane power and burn to 0% then evocate and burn to about 80 then conserve till you can magi+rune.
To conserve one single target just get to 4 stacks by casting arcane blast or arcane orb and barrage then restart.
You should be able to conjure mana gems that will give you 15% mana back as a consumable in combat with like a 3min cd.
Plus mage food which is a spell that creates food that restores 100% health and mana over 20s while eating.