Dual citizenship and application vs FAFSA application

I hold a dual citizenship (US and another Asian country) living abroad and in the verge of applying to a PhD program in UK. The school I am applying to has US FAFSA office. When I apply to the school using my Asian passport because my names on that legal document matches identically with my spelling and the name shown on my Diploma and transcripts, Will it effect or forbid me from benefiting from Financial Aid as I have recently applied for it and awaits my official acceptance? or It is a must that in order for me to get financial aid in a school abroad I must apply as an American citizen?

You must apply as a US citizen/permanent resident.

Not all Americans have a passport at all. But since you are an American living overseas, don’t you have a US passport?

Wouldn’t the PhD program be fully funded thus you’d have no need of the loans you might be eligible for after filing the FAFSA?

OP,
Don’t expect any grants from US Federal government for your PhD (at US or UK). Also you may want to research more on the Fulbright Commission which offers Postgraduate Student Awards for postgraduate studies at any accredited UK university (for US students only)

What kind of aid do you think you will net because you complete a FAFSA?

I think you should be able to file the FAFSA and get any federal benefits if the school is listed on the fafsa forms. However, all you’ll get most likely are unsubsidized loans because you are a grad student.

“It is a must that in order for me to get financial aid in a school abroad I must apply as an American citizen?”

This is a question that you must take directly to the financial aid office at the UK university in question. Let them know that you are dual-national, and that the version of your name on your US documents is not the same as the version on your other documents. Ask their experience with FAFSA. Ask if they will require that you file the FAFSA given your status as a US citizen. Ask if there will be any differences in eligibility for other aid, visa(s), work permission, etc. etc. depending on the documents you use if/when you do enroll. Sometimes citizenship status can have significant effects on those things.