How to name variables on the fly?

Use assign:

assign(paste("orca", i, sep = ""), list_name[[i]])

It seems to me that you might be better off with a list rather than using orca1, orca2, etc, ... then it would be orca[1], orca[2], ...

Usually you're making a list of variables differentiated by nothing but a number because that number would be a convenient way to access them later.

orca <- list()
orca[1] <- "Hi"
orca[2] <- 59

Otherwise, assign is just what you want.

Don't make data frames. Keep the list, name its elements but do not attach it.

The biggest reason for this is that if you make variables on the go, almost always you will later on have to iterate through each one of them to perform something useful. There you will again be forced to iterate through each one of the names that you have created on the fly.

It is far easier to name the elements of the list and iterate through the names.

As far as attach is concerned, its really bad programming practice in R and can lead to a lot of trouble if you are not careful.