why is this simple function slowing down, then crashing as time goes by

[benmartin101]

Here is the code:

		private void button1_Click(object sender, System.EventArgs e)
		{
			string s="aaaaaaaaaaT";
			for(int i=0;i<1000;i++)
			{
				func(ref s);
			}
			label1.Text = s;
	
		}

		private void func(ref string s)
		{
			s = s + s;
		}

My machine has about 710 MB left in the harddrive. When this program runs and "i" variable is at around 20, the functions slows down and eventually stops/crashes. I look at the taskmanager and it shows that the memory usage is at maximum. Is there a way around this?