Is alimony same as mahr muakhar?

No, it is not.

Mahr muakhar is what you agree upon at the time of the nikah. And you're basically saying that I'm giving you X amount right now. And if we get divorced, I'm giving you something at the end.

Alimony is state law enforced support of the wife after the divorce is over.

So the premise from which they come from are different, but you can structure your mahr muakhar so that it acts like alimony.

You could have a provision that says for each year that we are married, if we get divorced, you're going to pay me $10,000. So that could be a muakhar type of a payment.