which station in Barcelona does this train go to?

Hi Pat,
This link may make things a little clearer

.
https://en.wikipedia.org/wiki/Barcelona_Metro_line_9

You still catch the mainline surface train to Sants bu then catch the Metro to El Prat instead of that previous horrendous journey with all the hanging around at Sants etc.
As per the article :-

"One airport worker, who was among the first to travel on the 14.55hrs train using her T-Mes card, says being able to get to T1 directly by train was 'a luxury'.
“Beforehand, you had to catch the metro to T2, and then take a transit train which meant another half an hour's travelling,” she revealed.
Until now, travellers from outside Barcelona arriving by inter-provincial train at the main Sants station had to either add an hour to their journey to get to T1, or take a taxi costing upwards of €20.

Also, I Forgot to say I always buy a ticket at L'Aldea to barcelona airport. This is same cost as a ticket to Sants