Fluctuation Spectrum of Plasma with Few Electrons in Debye Volume Observed by Collective Light Scattering

The validity of the usual light‐scattering theory (i.e., $\text{Λ≫1}$ has been verified for $\text{Λ\hspace{0.17em}=\hspace{0.17em}2}$ , where ${\mathrm{\Lambda \hspace{0.17em}=\hspace{0.17em}N\lambda }}_D^3$ is the number of electrons in the Debye volume, $N$ is the electron density, and ${\lambda }_D$ is the Debye radius. Spectra of the light scattered from plasmas with $\text{Λ\hspace{0.17em}=\hspace{0.17em}2}$ and $\text{Λ\hspace{0.17em}=\hspace{0.17em}12}$ were measured and compared with the spectra predicted by $\text{Λ≫1}$ theory, with plasma parameters being independently obtained by the technique of plasma spectroscopy. Comparison between the plasma parameters ${\text{(n\hspace{0.17em}=\hspace{0.17em}2−3×10}}^{17}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}\text{,\hspace{0.17em}T\hspace{0.17em}=\hspace{0.17em}2−6\hspace{0.17em}eV)}$ determined from scattered light and those deduced from spectroscopic measurement was also made. It was found that they agreed within the experimental errors.