Unsual alternator problem

Hi guys, my car has recently been cutting out at low revs or when sat in traffic, and the alternator light comes on, and obviously because the power has gone i lose my power steering and brakes which is very dangerous, then when i go to turn it back over there is nothing, not even trying to turn over, then 15 mins or so later it will start again fine but is an ongoing problem, the aa have looked at it twice now and cannot seem to find out the problem

my car is a 1.7 turbo diesel 08 reg

sounds like you alternator might be going out, might want to take it off and have it tested at a auto parts store or get a voltmeter that plug into lighter socket so you can keep a eye on the voltage