Herriott Cell Interferometery for Millimeter-Scale Plasma Measurements
Abstract
A Herriott Cell consists of two concave mirrors positioned on opposite sides of plasma so as to create multiple laser paths through the plasma. Added to a traditional interferometry diagnostic, the Herriott Cell multiplies the effective path length through the medium and thereby increases instrument resolution. Previous work validated the use of Herriott Cells in interferometer applications where the numerous mirror reflections will significantly degrade the phase front quality. The previous work used a planar configuration where collimated beams were retro-reflected across the exit plane of a plasma thruster. The current work extends the Herriott Cell capability to a point configuration. In this geometry the multi-pass beams converge near a single point within the plasma, useful for performing density measurements in very small scale length plasmas. Ray tracing analysis is used to illustrate example measurement geometries attainable with the instrument. It is shown that the configuration results in two convergence points for the laser paths, which somewhat complicates the interpretation of the experimental data. The diagnostic capability is demonstrated with measurements of the electron and neutral densities in the plasma exhaust of a Micro Pulsed Plasma Thruster. The measurements are validated with similar, lower resolution measurements, obtained using a single-pass interferometer.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 03, 2002
- Accession Number
- ADA405831
Entities
People
- Erik L. Antonsen
- Gregory G. Spanjers
- Rodney L. Burton
- Scott F. Engelman
Organizations
- Air Force Research Laboratory