Basically its in the name, The idea would be instead of purchasing tickets by cash you purchase them by credits. I think this should be 1 week in every 4 week period that you do this. The reason being it's unfair on the players that don't have credits and may have a little cash laying around to buy a few tickets.

or you could do it everyweek just Credits instead of cash run them both as different lottery's

Or you could make it so it isn't 1 credit per ticket, 0.1 of a credit for example could be used.

On the other hand, I don't really see this as necessary... I mean what you could just sell the credit/s you would put into a credit lottery and use the money for the normal lottery that's already held each week, then buy credits with the money if you win...