Can a landlord ask for double deposit if on section 8 I am in California?

Of course, they can! It is their property. The funds go into escrow to be used for that purpose only. Make sure you complete a walk through list when you first move in. When you move out, take your copy of the list and walk through the apartment with them. Many of them charge for loose electrical outlets, dings on doors and other ridiculous charges if you do not attend the the walkthough at the end. Make sure you keep up with the maintenance of the place and document your requests.