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This book is from the late 80s at the earliest; I read it around 1988). Here is the synopsis:
A young man on the cusp of becoming an adult is to take a test mandated by the Empire (Emperor) called the Fortune Hunter Test or something. Basically it is a test that is supposed to set you on your life path and some 'very lucky' people who pass it are taken to special schools and never seen again but assumed to be filthy rich or whatever.
The kid takes test and is one of the lucky ones and they take him through a matter transmitter called an MT Screen or Empty Screen. It is gray and opaque. The kid is (fuzzy on this part, as I was like 11 or something and sick) rescued or escapes or something and goes on the run after realizing that the Emperor is actually culling out the people who are lucky or smart enough to threaten his reign.
The kid ends up fighting the for a rebel group that is part of an interstellar circus or something as a cover. They have all this tech based on the matter transmitters including a MT cube that is basically projected around the person as a shield but can have the walls removed so they can be shot then have them pop back into existence to protect the person inside. Also the mt screen can be weaponized as it instantaneously transmits matter that it touches to another place and can therefore be used as a slicer to remove parts of people or whatnot (Kind of violent theoretically, but not really that bloody).
At one point the kid is trying to get past a security checkpoint and the ringmaster (I think) gives him the identity Asa Baqua (spelling?) who we later find out was his child who maybe passed the fortune hunters test before, and disappeared, giving the ringmaster (weird word but that is what I remember) a reason to fight against the emperor.
Anyway, it was teen fiction or sci fi/fantasy and I loved the story but only read it once forever ago. If anyone can figure out this book or remembers having read it please let me know!