Dear Watson,
Possibilities in finding out what Papp knew.
One way is to find out where he studied, and what projects he worked on in that time.
Plus later on he joined the military, became a pilot and may have had excess to military science documents.
Also it may be of interest, what in those days in that country, where the sources of science that covered gases and plasma etc.
Could be mainly Russian science.
But him being hungarian(?) if there would have been some fellow countryman doing something in the mentioned field, then Papp would have read that with more eager then the russian stuff i guess.
It may also be interesting to find what other sources were open to Papp when he came to America. So what science was done in his field in those days?
Wasn't there some other fellow in his beginning days that claimed a similar invention?
Follow these clue's and report back a.s.a.p.
S.Holmes