Inside the high-temperature plasma core of a stellarator, two protons are separated by a distance rrr. The electrostatic force of repulsion between these two protons is X X\,X times the gravitational force of attraction between them.
What is the best estimate for XXX?
103010^{30}1030
103610^{36}1036
103910^{39}1039
104210^{42}1042
