I acted in self defense against an attacker and am being charged with assault. Is there any Assault Defense law?

Even though you admit that the assault took place, you still have some options regarding an assault defense.  In an affirmative defense, you, the defendant, accept that the elements of the crime have been shown, but can argue that the act was justified and should be excused.  Even a person charged with a violent crime can be acquitted if he proves that he was justified in using the force involved in the crime.  Another assault defense would be if you could establish that you were forced by another to commit the crime and had no alternative but to do so.  I would suggest consulting with an attorney experienced in criminal defense who would be qualified to discuss assault defenses with you.