You could start using poison, chemicals or more biologic repellent liquids against ants, but ants probably still will come.
The best way is to reduce (actually to remove) any kind of attractions they like: food and water. If they cannot find anything useful, than they will stop releasing scents that attracted other ants.
This means, you have to make sure there is no (open) water or drinks nearby, no sugar in any way, and no food in general. Keep everything enclosed, in such a way it doesn't smell, there is no opening and clean up everything fast after use (better, eat and use food/drink away from your tent).
It can take a few days before the scents the ants are releasing will go, but the above will help.