Pressure in an experimental fusion device is $5$e$8$ mbar $($millibar$,1$ bar $=105$ Pascal$).$ Assuming that the gas is pure in atomic state whose first ionization energy is $2200,($In $1$ mol, there are $6\mathrm{.}02$e$23$ particles$),$ and the gas is ideal $($p$=$NTotal.kB$.$T$)$ calculate the ionization fraction $($ Ni$/($Ni$+$Nn$))$ at the temperature $8000$Kelvin