Applying for VISAs and travelling to LA in general?

You don't need a visa to visit from from Northern Ireland. Just apply on line for the "ESTA" program before departing. The website is "www.cpb.gov" You can stay in the U.S. on the ESTA (formerly called a Visa Waiver) for up to 90 days. I believe the cost is $14 U.S. Enjoy your stay in Los Angeles.