The He II 304-Å line emitted from a $N_e\approx 3\times {10}^{17}$-${\mathrm{cm}}^{-3\mathrm{}}$,, $T_e\approx 4$-eV plasma in a $T$-type electric shock tube shows a blue shift of ∼0.05 Å. This shift is interpreted as due to the negative space charge from the polarization of plasma regions occupied by positive ions.

• Received 29 October 1969

DOI:https://doi.org/10.1103/PhysRevLett.24.3