Plasma Resonance and Standing Longitudinal Electron Waves

Using an electron beam probe, the existence of a standing electrostatic wave in the sheath surrounding a planar probe immersed in a plasma when the probe is driven at frequencies near ${\omega }_p$ has been demonstrated. The driven probe exhibits two admittance resonances. The larger of these $(\mathrm{near}\hspace{0.17em}\frac{1}{2}{\omega }_p)$ is the well documented “resonance probe” resonance. The smaller second resonance at ${\mathrm{\omega \approx \omega }}_p$ is associated with the standing wave and its interpretation as a Tonks‐Dattner resonance is discussed. The effect of such a standing wave on the usual interpretation of plasma resonance probe data is examined.