The LC resonance probe for determining local plasma density

We present a novel plasma diagnostic for measuring local plasma density in reactive-gas plasmas, and depositing plasmas. The diagnostic uses a network analyzer to measure the LC resonance (LCR) frequency of a parallel plate capacitor with inductive leads. The location of the LCR (ωR) in frequency space is then used as a measure of the plasma dielectric constant bold varepsilonp between the plates. By properly constructing the LCR probe, ωR can be tuned such that ωR >> ωce, where ωce is the electron-cyclotron frequency. Thus, the probe can be used in plasmas with varying degrees of magnetization while avoiding complications introduced to bold varepsilonp when ω is comparable to ωce. Density measurements from the LCR probe are compared with Langmuir probe measurements in an electron-beam generated plasma in which density varied from 109 to 1011 cm-3. An axial magnetic field, typically used to confine the electron beam, was varied between 0 to 300 G. The LCR probe showed good agreement with a Langmuir probe across the entire range of magnetic fields.