1.) Is there a way to get more AP than 4 (psy power, cybernetic, talent) ?

2.) If you have an attack psionic power, which has e.g. a RoF of 1/2 and the power in general needs 2 AP to be casted...how does that work wit the RoF ?

Can I spent 4 AP for the power to make a double hit ?

1. I don't believe so.

2. AFAIK, there are no attack psi powers with RoF 1/2. Most are given a rate of ATTACK, not a rate of fire, so you cannot spend more AP to get more potential hits - the RoA is already the maximum number of hits you can get in a round. Also see p. 172: "If the character uses a psychic power with the attack action type, that is the only attack action the character can make that turn, even if he is wielding two weapons." Put simply, if you want to spam psychic blasts, your best bet is Smite. Otherwise, you'll have to be content with one psychic attack per round, yielding (in most cases) one hit per round.

The good news is, there are lots of of powers that come with special effects (daze, potential stun, spray, weakness, etc.) The design of 2nd ed. psyker attacks seems more geared towards "do okay damage and reduce the effectiveness of the enemy," rather than "do a lot of raw damage."

1. There are a few talents that allow you to reduce the AP cost of certain actions, but actually gaining more AP is not possible afaik.

2. easl is right, the only psychic power that goes over RoA 1 is Smite.