The 21-year old defender has signed a one-month deal with Pompey as he looks to gain experience in a regular first team environment in League Two.
"It's exactly what I've been looking for - a massive club to come to and play some football," he told Portsmouth's official website.
"There are big crowds here and it's the perfect move at this stage of my career.
"I've been in the reserves at Swansea, but I really need to be playing first-team football and I want help this club out.
"I think of myself as an attacking right-back, so hopefully I can get some assists and maybe a goal or two.
"As a defender I have to concentrate on helping the side not to concede, but I like to get forward as well."
Alfei came through Swansea's youth academy before joining the senior ranks in 2010 and has appeared three times for the Jacks. He has also had two loan spells with Wrexham which came in 2012 and 2013.
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