I think bottom assumption was a hydrogen atom every cubic centameter or 4. Don't understand you question. Sorry for the slang. English to englist translation. I don't know what the answer is.
Ions are particles too.
I don't agree with that. Sorry that won't work. This of course ignores the fact the sail isn't rigid, and will tend to crumple once its free of the ship. Forward realized this, thats why he had an army of autonomus robots go with the outer sail to keep it working.