Study of a High-Power, Pulsed Plasma Jet with a Heterodyne Interferometer*

Presented is a method to measure the line-averaged electron density and velocity of a plasma jet generated by a pulsed plasma source, using a heterodyne interferometer. This source will produce a plasma jet that exhibits instabilities [1] and magnetic reconnection [2] inside Embry-Riddle’s two meter long, cylindrical plasma chamber. A heterodyne interferometer is similar to a Michelson interferometer, with the difference that the non-plasma beam is passed through an acoustic-optical modulator that isolates the 1st harmonic of the beam[3]. A fiber optic cable is used to transmit the scene beam to the vacuum chamber from the optics bench and back, allowing easy variation to sampling location across experiments. The Interferometer measures the change in the index of refraction of the plasma chamber, this enables the determination of the change of the line-averaged electron density of the plasma jet [4]. By interpreting this data over system parameter variations, changes in the density of the plasma jet over the course of the experiment will be studied. This study will investigate fundamental plasma physics and applications, such as the drivers and patterns of reconnection and may lead to improved fusion energy generation and pulsed plasma propulsion. 

 

References:  

[1] Hsu, S., Bellan, P. (2005) On the jets, kinks, and spheromaks formed by a planar magnetized coaxial gun. Physics of Plasmas,12 (3): 032103. https://doi.org/10.1063/1.1850921 

[2] Seo, B., Wongwaitayakornkul, P., Haw, Magnus. A., Marshall, Ryan S., Li, Hui, and Bellan, P. (2020) Determination of macro to microscale progression leading to a magnetized plasma disruption, Physics of plasmas, 27, 022109 

[3] Kumar, D. (2006) Heterodyne interferometer with unequal path lengths. Review of Scientific Instruments, 77, 083503. 

[4] Seo, B.,Bellan, P. (2017) Spatially translatable optical fiber-coupled heterodyne interferometer. Review of Scientific Instruments, 88 (12): 123504. https://doi.org/10.1063/1.5007070